Age Owner Branch data TLA Line data Source code
1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * procarray.c
4 : : * POSTGRES process array code.
5 : : *
6 : : *
7 : : * This module maintains arrays of PGPROC substructures, as well as associated
8 : : * arrays in ProcGlobal, for all active backends. Although there are several
9 : : * uses for this, the principal one is as a means of determining the set of
10 : : * currently running transactions.
11 : : *
12 : : * Because of various subtle race conditions it is critical that a backend
13 : : * hold the correct locks while setting or clearing its xid (in
14 : : * ProcGlobal->xids[]/MyProc->xid). See notes in
15 : : * src/backend/access/transam/README.
16 : : *
17 : : * The process arrays now also include structures representing prepared
18 : : * transactions. The xid and subxids fields of these are valid, as are the
19 : : * myProcLocks lists. They can be distinguished from regular backend PGPROCs
20 : : * at need by checking for pid == 0.
21 : : *
22 : : * During hot standby, we also keep a list of XIDs representing transactions
23 : : * that are known to be running on the primary (or more precisely, were running
24 : : * as of the current point in the WAL stream). This list is kept in the
25 : : * KnownAssignedXids array, and is updated by watching the sequence of
26 : : * arriving XIDs. This is necessary because if we leave those XIDs out of
27 : : * snapshots taken for standby queries, then they will appear to be already
28 : : * complete, leading to MVCC failures. Note that in hot standby, the PGPROC
29 : : * array represents standby processes, which by definition are not running
30 : : * transactions that have XIDs.
31 : : *
32 : : * It is perhaps possible for a backend on the primary to terminate without
33 : : * writing an abort record for its transaction. While that shouldn't really
34 : : * happen, it would tie up KnownAssignedXids indefinitely, so we protect
35 : : * ourselves by pruning the array when a valid list of running XIDs arrives.
36 : : *
37 : : * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
38 : : * Portions Copyright (c) 1994, Regents of the University of California
39 : : *
40 : : *
41 : : * IDENTIFICATION
42 : : * src/backend/storage/ipc/procarray.c
43 : : *
44 : : *-------------------------------------------------------------------------
45 : : */
46 : : #include "postgres.h"
47 : :
48 : : #include <signal.h>
49 : :
50 : : #include "access/subtrans.h"
51 : : #include "access/transam.h"
52 : : #include "access/twophase.h"
53 : : #include "access/xact.h"
54 : : #include "access/xlogutils.h"
55 : : #include "catalog/catalog.h"
56 : : #include "catalog/pg_authid.h"
57 : : #include "commands/dbcommands.h"
58 : : #include "miscadmin.h"
59 : : #include "pgstat.h"
60 : : #include "port/pg_lfind.h"
61 : : #include "storage/proc.h"
62 : : #include "storage/procarray.h"
63 : : #include "utils/acl.h"
64 : : #include "utils/builtins.h"
65 : : #include "utils/rel.h"
66 : : #include "utils/snapmgr.h"
67 : :
68 : : #define UINT32_ACCESS_ONCE(var) ((uint32)(*((volatile uint32 *)&(var))))
69 : :
70 : : /* Our shared memory area */
71 : : typedef struct ProcArrayStruct
72 : : {
73 : : int numProcs; /* number of valid procs entries */
74 : : int maxProcs; /* allocated size of procs array */
75 : :
76 : : /*
77 : : * Known assigned XIDs handling
78 : : */
79 : : int maxKnownAssignedXids; /* allocated size of array */
80 : : int numKnownAssignedXids; /* current # of valid entries */
81 : : int tailKnownAssignedXids; /* index of oldest valid element */
82 : : int headKnownAssignedXids; /* index of newest element, + 1 */
83 : :
84 : : /*
85 : : * Highest subxid that has been removed from KnownAssignedXids array to
86 : : * prevent overflow; or InvalidTransactionId if none. We track this for
87 : : * similar reasons to tracking overflowing cached subxids in PGPROC
88 : : * entries. Must hold exclusive ProcArrayLock to change this, and shared
89 : : * lock to read it.
90 : : */
91 : : TransactionId lastOverflowedXid;
92 : :
93 : : /* oldest xmin of any replication slot */
94 : : TransactionId replication_slot_xmin;
95 : : /* oldest catalog xmin of any replication slot */
96 : : TransactionId replication_slot_catalog_xmin;
97 : :
98 : : /* indexes into allProcs[], has PROCARRAY_MAXPROCS entries */
99 : : int pgprocnos[FLEXIBLE_ARRAY_MEMBER];
100 : : } ProcArrayStruct;
101 : :
102 : : /*
103 : : * State for the GlobalVisTest* family of functions. Those functions can
104 : : * e.g. be used to decide if a deleted row can be removed without violating
105 : : * MVCC semantics: If the deleted row's xmax is not considered to be running
106 : : * by anyone, the row can be removed.
107 : : *
108 : : * To avoid slowing down GetSnapshotData(), we don't calculate a precise
109 : : * cutoff XID while building a snapshot (looking at the frequently changing
110 : : * xmins scales badly). Instead we compute two boundaries while building the
111 : : * snapshot:
112 : : *
113 : : * 1) definitely_needed, indicating that rows deleted by XIDs >=
114 : : * definitely_needed are definitely still visible.
115 : : *
116 : : * 2) maybe_needed, indicating that rows deleted by XIDs < maybe_needed can
117 : : * definitely be removed
118 : : *
119 : : * When testing an XID that falls in between the two (i.e. XID >= maybe_needed
120 : : * && XID < definitely_needed), the boundaries can be recomputed (using
121 : : * ComputeXidHorizons()) to get a more accurate answer. This is cheaper than
122 : : * maintaining an accurate value all the time.
123 : : *
124 : : * As it is not cheap to compute accurate boundaries, we limit the number of
125 : : * times that happens in short succession. See GlobalVisTestShouldUpdate().
126 : : *
127 : : *
128 : : * There are three backend lifetime instances of this struct, optimized for
129 : : * different types of relations. As e.g. a normal user defined table in one
130 : : * database is inaccessible to backends connected to another database, a test
131 : : * specific to a relation can be more aggressive than a test for a shared
132 : : * relation. Currently we track four different states:
133 : : *
134 : : * 1) GlobalVisSharedRels, which only considers an XID's
135 : : * effects visible-to-everyone if neither snapshots in any database, nor a
136 : : * replication slot's xmin, nor a replication slot's catalog_xmin might
137 : : * still consider XID as running.
138 : : *
139 : : * 2) GlobalVisCatalogRels, which only considers an XID's
140 : : * effects visible-to-everyone if neither snapshots in the current
141 : : * database, nor a replication slot's xmin, nor a replication slot's
142 : : * catalog_xmin might still consider XID as running.
143 : : *
144 : : * I.e. the difference to GlobalVisSharedRels is that
145 : : * snapshot in other databases are ignored.
146 : : *
147 : : * 3) GlobalVisDataRels, which only considers an XID's
148 : : * effects visible-to-everyone if neither snapshots in the current
149 : : * database, nor a replication slot's xmin consider XID as running.
150 : : *
151 : : * I.e. the difference to GlobalVisCatalogRels is that
152 : : * replication slot's catalog_xmin is not taken into account.
153 : : *
154 : : * 4) GlobalVisTempRels, which only considers the current session, as temp
155 : : * tables are not visible to other sessions.
156 : : *
157 : : * GlobalVisTestFor(relation) returns the appropriate state
158 : : * for the relation.
159 : : *
160 : : * The boundaries are FullTransactionIds instead of TransactionIds to avoid
161 : : * wraparound dangers. There e.g. would otherwise exist no procarray state to
162 : : * prevent maybe_needed to become old enough after the GetSnapshotData()
163 : : * call.
164 : : *
165 : : * The typedef is in the header.
166 : : */
167 : : struct GlobalVisState
168 : : {
169 : : /* XIDs >= are considered running by some backend */
170 : : FullTransactionId definitely_needed;
171 : :
172 : : /* XIDs < are not considered to be running by any backend */
173 : : FullTransactionId maybe_needed;
174 : : };
175 : :
176 : : /*
177 : : * Result of ComputeXidHorizons().
178 : : */
179 : : typedef struct ComputeXidHorizonsResult
180 : : {
181 : : /*
182 : : * The value of TransamVariables->latestCompletedXid when
183 : : * ComputeXidHorizons() held ProcArrayLock.
184 : : */
185 : : FullTransactionId latest_completed;
186 : :
187 : : /*
188 : : * The same for procArray->replication_slot_xmin and.
189 : : * procArray->replication_slot_catalog_xmin.
190 : : */
191 : : TransactionId slot_xmin;
192 : : TransactionId slot_catalog_xmin;
193 : :
194 : : /*
195 : : * Oldest xid that any backend might still consider running. This needs to
196 : : * include processes running VACUUM, in contrast to the normal visibility
197 : : * cutoffs, as vacuum needs to be able to perform pg_subtrans lookups when
198 : : * determining visibility, but doesn't care about rows above its xmin to
199 : : * be removed.
200 : : *
201 : : * This likely should only be needed to determine whether pg_subtrans can
202 : : * be truncated. It currently includes the effects of replication slots,
203 : : * for historical reasons. But that could likely be changed.
204 : : */
205 : : TransactionId oldest_considered_running;
206 : :
207 : : /*
208 : : * Oldest xid for which deleted tuples need to be retained in shared
209 : : * tables.
210 : : *
211 : : * This includes the effects of replication slots. If that's not desired,
212 : : * look at shared_oldest_nonremovable_raw;
213 : : */
214 : : TransactionId shared_oldest_nonremovable;
215 : :
216 : : /*
217 : : * Oldest xid that may be necessary to retain in shared tables. This is
218 : : * the same as shared_oldest_nonremovable, except that is not affected by
219 : : * replication slot's catalog_xmin.
220 : : *
221 : : * This is mainly useful to be able to send the catalog_xmin to upstream
222 : : * streaming replication servers via hot_standby_feedback, so they can
223 : : * apply the limit only when accessing catalog tables.
224 : : */
225 : : TransactionId shared_oldest_nonremovable_raw;
226 : :
227 : : /*
228 : : * Oldest xid for which deleted tuples need to be retained in non-shared
229 : : * catalog tables.
230 : : */
231 : : TransactionId catalog_oldest_nonremovable;
232 : :
233 : : /*
234 : : * Oldest xid for which deleted tuples need to be retained in normal user
235 : : * defined tables.
236 : : */
237 : : TransactionId data_oldest_nonremovable;
238 : :
239 : : /*
240 : : * Oldest xid for which deleted tuples need to be retained in this
241 : : * session's temporary tables.
242 : : */
243 : : TransactionId temp_oldest_nonremovable;
244 : : } ComputeXidHorizonsResult;
245 : :
246 : : /*
247 : : * Return value for GlobalVisHorizonKindForRel().
248 : : */
249 : : typedef enum GlobalVisHorizonKind
250 : : {
251 : : VISHORIZON_SHARED,
252 : : VISHORIZON_CATALOG,
253 : : VISHORIZON_DATA,
254 : : VISHORIZON_TEMP,
255 : : } GlobalVisHorizonKind;
256 : :
257 : : /*
258 : : * Reason codes for KnownAssignedXidsCompress().
259 : : */
260 : : typedef enum KAXCompressReason
261 : : {
262 : : KAX_NO_SPACE, /* need to free up space at array end */
263 : : KAX_PRUNE, /* we just pruned old entries */
264 : : KAX_TRANSACTION_END, /* we just committed/removed some XIDs */
265 : : KAX_STARTUP_PROCESS_IDLE, /* startup process is about to sleep */
266 : : } KAXCompressReason;
267 : :
268 : :
269 : : static ProcArrayStruct *procArray;
270 : :
271 : : static PGPROC *allProcs;
272 : :
273 : : /*
274 : : * Cache to reduce overhead of repeated calls to TransactionIdIsInProgress()
275 : : */
276 : : static TransactionId cachedXidIsNotInProgress = InvalidTransactionId;
277 : :
278 : : /*
279 : : * Bookkeeping for tracking emulated transactions in recovery
280 : : */
281 : : static TransactionId *KnownAssignedXids;
282 : : static bool *KnownAssignedXidsValid;
283 : : static TransactionId latestObservedXid = InvalidTransactionId;
284 : :
285 : : /*
286 : : * If we're in STANDBY_SNAPSHOT_PENDING state, standbySnapshotPendingXmin is
287 : : * the highest xid that might still be running that we don't have in
288 : : * KnownAssignedXids.
289 : : */
290 : : static TransactionId standbySnapshotPendingXmin;
291 : :
292 : : /*
293 : : * State for visibility checks on different types of relations. See struct
294 : : * GlobalVisState for details. As shared, catalog, normal and temporary
295 : : * relations can have different horizons, one such state exists for each.
296 : : */
297 : : static GlobalVisState GlobalVisSharedRels;
298 : : static GlobalVisState GlobalVisCatalogRels;
299 : : static GlobalVisState GlobalVisDataRels;
300 : : static GlobalVisState GlobalVisTempRels;
301 : :
302 : : /*
303 : : * This backend's RecentXmin at the last time the accurate xmin horizon was
304 : : * recomputed, or InvalidTransactionId if it has not. Used to limit how many
305 : : * times accurate horizons are recomputed. See GlobalVisTestShouldUpdate().
306 : : */
307 : : static TransactionId ComputeXidHorizonsResultLastXmin;
308 : :
309 : : #ifdef XIDCACHE_DEBUG
310 : :
311 : : /* counters for XidCache measurement */
312 : : static long xc_by_recent_xmin = 0;
313 : : static long xc_by_known_xact = 0;
314 : : static long xc_by_my_xact = 0;
315 : : static long xc_by_latest_xid = 0;
316 : : static long xc_by_main_xid = 0;
317 : : static long xc_by_child_xid = 0;
318 : : static long xc_by_known_assigned = 0;
319 : : static long xc_no_overflow = 0;
320 : : static long xc_slow_answer = 0;
321 : :
322 : : #define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
323 : : #define xc_by_known_xact_inc() (xc_by_known_xact++)
324 : : #define xc_by_my_xact_inc() (xc_by_my_xact++)
325 : : #define xc_by_latest_xid_inc() (xc_by_latest_xid++)
326 : : #define xc_by_main_xid_inc() (xc_by_main_xid++)
327 : : #define xc_by_child_xid_inc() (xc_by_child_xid++)
328 : : #define xc_by_known_assigned_inc() (xc_by_known_assigned++)
329 : : #define xc_no_overflow_inc() (xc_no_overflow++)
330 : : #define xc_slow_answer_inc() (xc_slow_answer++)
331 : :
332 : : static void DisplayXidCache(void);
333 : : #else /* !XIDCACHE_DEBUG */
334 : :
335 : : #define xc_by_recent_xmin_inc() ((void) 0)
336 : : #define xc_by_known_xact_inc() ((void) 0)
337 : : #define xc_by_my_xact_inc() ((void) 0)
338 : : #define xc_by_latest_xid_inc() ((void) 0)
339 : : #define xc_by_main_xid_inc() ((void) 0)
340 : : #define xc_by_child_xid_inc() ((void) 0)
341 : : #define xc_by_known_assigned_inc() ((void) 0)
342 : : #define xc_no_overflow_inc() ((void) 0)
343 : : #define xc_slow_answer_inc() ((void) 0)
344 : : #endif /* XIDCACHE_DEBUG */
345 : :
346 : : /* Primitives for KnownAssignedXids array handling for standby */
347 : : static void KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock);
348 : : static void KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
349 : : bool exclusive_lock);
350 : : static bool KnownAssignedXidsSearch(TransactionId xid, bool remove);
351 : : static bool KnownAssignedXidExists(TransactionId xid);
352 : : static void KnownAssignedXidsRemove(TransactionId xid);
353 : : static void KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
354 : : TransactionId *subxids);
355 : : static void KnownAssignedXidsRemovePreceding(TransactionId removeXid);
356 : : static int KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax);
357 : : static int KnownAssignedXidsGetAndSetXmin(TransactionId *xarray,
358 : : TransactionId *xmin,
359 : : TransactionId xmax);
360 : : static TransactionId KnownAssignedXidsGetOldestXmin(void);
361 : : static void KnownAssignedXidsDisplay(int trace_level);
362 : : static void KnownAssignedXidsReset(void);
363 : : static inline void ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid);
364 : : static void ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid);
365 : : static void MaintainLatestCompletedXid(TransactionId latestXid);
366 : : static void MaintainLatestCompletedXidRecovery(TransactionId latestXid);
367 : :
368 : : static inline FullTransactionId FullXidRelativeTo(FullTransactionId rel,
369 : : TransactionId xid);
370 : : static void GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons);
371 : :
372 : : /*
373 : : * Report shared-memory space needed by CreateSharedProcArray.
374 : : */
375 : : Size
6876 tgl@sss.pgh.pa.us 376 :CBC 1679 : ProcArrayShmemSize(void)
377 : : {
378 : : Size size;
379 : :
380 : : /* Size of the ProcArray structure itself */
381 : : #define PROCARRAY_MAXPROCS (MaxBackends + max_prepared_xacts)
382 : :
4524 rhaas@postgresql.org 383 : 1679 : size = offsetof(ProcArrayStruct, pgprocnos);
733 384 : 1679 : size = add_size(size, mul_size(sizeof(int), PROCARRAY_MAXPROCS));
385 : :
386 : : /*
387 : : * During Hot Standby processing we have a data structure called
388 : : * KnownAssignedXids, created in shared memory. Local data structures are
389 : : * also created in various backends during GetSnapshotData(),
390 : : * TransactionIdIsInProgress() and GetRunningTransactionData(). All of the
391 : : * main structures created in those functions must be identically sized,
392 : : * since we may at times copy the whole of the data structures around. We
393 : : * refer to this size as TOTAL_MAX_CACHED_SUBXIDS.
394 : : *
395 : : * Ideally we'd only create this structure if we were actually doing hot
396 : : * standby in the current run, but we don't know that yet at the time
397 : : * shared memory is being set up.
398 : : */
399 : : #define TOTAL_MAX_CACHED_SUBXIDS \
400 : : ((PGPROC_MAX_CACHED_SUBXIDS + 1) * PROCARRAY_MAXPROCS)
401 : :
5099 tgl@sss.pgh.pa.us 402 [ + + ]: 1679 : if (EnableHotStandby)
403 : : {
5100 404 : 1669 : size = add_size(size,
405 : : mul_size(sizeof(TransactionId),
406 : 1669 : TOTAL_MAX_CACHED_SUBXIDS));
5202 407 : 1669 : size = add_size(size,
5100 408 : 1669 : mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS));
409 : : }
410 : :
6812 411 : 1679 : return size;
412 : : }
413 : :
414 : : /*
415 : : * Initialize the shared PGPROC array during postmaster startup.
416 : : */
417 : : void
6876 418 : 898 : CreateSharedProcArray(void)
419 : : {
420 : : bool found;
421 : :
422 : : /* Create or attach to the ProcArray shared structure */
6905 423 : 898 : procArray = (ProcArrayStruct *)
5230 simon@2ndQuadrant.co 424 : 898 : ShmemInitStruct("Proc Array",
425 : : add_size(offsetof(ProcArrayStruct, pgprocnos),
426 : : mul_size(sizeof(int),
733 rhaas@postgresql.org 427 : 898 : PROCARRAY_MAXPROCS)),
428 : : &found);
429 : :
6905 tgl@sss.pgh.pa.us 430 [ + - ]: 898 : if (!found)
431 : : {
432 : : /*
433 : : * We're the first - initialize.
434 : : */
435 : 898 : procArray->numProcs = 0;
733 rhaas@postgresql.org 436 : 898 : procArray->maxProcs = PROCARRAY_MAXPROCS;
5202 tgl@sss.pgh.pa.us 437 : 898 : procArray->maxKnownAssignedXids = TOTAL_MAX_CACHED_SUBXIDS;
5100 438 : 898 : procArray->numKnownAssignedXids = 0;
439 : 898 : procArray->tailKnownAssignedXids = 0;
440 : 898 : procArray->headKnownAssignedXids = 0;
5202 441 : 898 : procArray->lastOverflowedXid = InvalidTransactionId;
2434 peter_e@gmx.net 442 : 898 : procArray->replication_slot_xmin = InvalidTransactionId;
443 : 898 : procArray->replication_slot_catalog_xmin = InvalidTransactionId;
128 heikki.linnakangas@i 444 :GNC 898 : TransamVariables->xactCompletionCount = 1;
445 : : }
446 : :
4524 rhaas@postgresql.org 447 :CBC 898 : allProcs = ProcGlobal->allProcs;
448 : :
449 : : /* Create or attach to the KnownAssignedXids arrays too, if needed */
5099 tgl@sss.pgh.pa.us 450 [ + + ]: 898 : if (EnableHotStandby)
451 : : {
5100 452 : 893 : KnownAssignedXids = (TransactionId *)
453 : 893 : ShmemInitStruct("KnownAssignedXids",
454 : : mul_size(sizeof(TransactionId),
455 : 893 : TOTAL_MAX_CACHED_SUBXIDS),
456 : : &found);
457 : 893 : KnownAssignedXidsValid = (bool *)
458 : 893 : ShmemInitStruct("KnownAssignedXidsValid",
459 : 893 : mul_size(sizeof(bool), TOTAL_MAX_CACHED_SUBXIDS),
460 : : &found);
461 : : }
6905 462 : 898 : }
463 : :
464 : : /*
465 : : * Add the specified PGPROC to the shared array.
466 : : */
467 : : void
6876 468 : 16764 : ProcArrayAdd(PGPROC *proc)
469 : : {
52 heikki.linnakangas@i 470 :GNC 16764 : int pgprocno = GetNumberFromPGProc(proc);
6905 tgl@sss.pgh.pa.us 471 :CBC 16764 : ProcArrayStruct *arrayP = procArray;
472 : : int index;
473 : : int movecount;
474 : :
475 : : /* See ProcGlobal comment explaining why both locks are held */
476 : 16764 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1339 andres@anarazel.de 477 : 16764 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
478 : :
6905 tgl@sss.pgh.pa.us 479 [ - + ]: 16764 : if (arrayP->numProcs >= arrayP->maxProcs)
480 : : {
481 : : /*
482 : : * Oops, no room. (This really shouldn't happen, since there is a
483 : : * fixed supply of PGPROC structs too, and so we should have failed
484 : : * earlier.)
485 : : */
6905 tgl@sss.pgh.pa.us 486 [ # # ]:UBC 0 : ereport(FATAL,
487 : : (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
488 : : errmsg("sorry, too many clients already")));
489 : : }
490 : :
491 : : /*
492 : : * Keep the procs array sorted by (PGPROC *) so that we can utilize
493 : : * locality of references much better. This is useful while traversing the
494 : : * ProcArray because there is an increased likelihood of finding the next
495 : : * PGPROC structure in the cache.
496 : : *
497 : : * Since the occurrence of adding/removing a proc is much lower than the
498 : : * access to the ProcArray itself, the overhead should be marginal
499 : : */
4524 rhaas@postgresql.org 500 [ + + ]:CBC 39760 : for (index = 0; index < arrayP->numProcs; index++)
501 : : {
52 heikki.linnakangas@i 502 :GNC 35748 : int this_procno = arrayP->pgprocnos[index];
503 : :
504 [ + - - + ]: 35748 : Assert(this_procno >= 0 && this_procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
505 [ - + ]: 35748 : Assert(allProcs[this_procno].pgxactoff == index);
506 : :
507 : : /* If we have found our right position in the array, break */
508 [ + + ]: 35748 : if (this_procno > pgprocno)
4524 rhaas@postgresql.org 509 :CBC 12752 : break;
510 : : }
511 : :
1038 andres@anarazel.de 512 : 16764 : movecount = arrayP->numProcs - index;
513 : 16764 : memmove(&arrayP->pgprocnos[index + 1],
514 : 16764 : &arrayP->pgprocnos[index],
515 : : movecount * sizeof(*arrayP->pgprocnos));
516 : 16764 : memmove(&ProcGlobal->xids[index + 1],
517 : 16764 : &ProcGlobal->xids[index],
518 : : movecount * sizeof(*ProcGlobal->xids));
519 : 16764 : memmove(&ProcGlobal->subxidStates[index + 1],
520 : 16764 : &ProcGlobal->subxidStates[index],
521 : : movecount * sizeof(*ProcGlobal->subxidStates));
522 : 16764 : memmove(&ProcGlobal->statusFlags[index + 1],
523 : 16764 : &ProcGlobal->statusFlags[index],
524 : : movecount * sizeof(*ProcGlobal->statusFlags));
525 : :
52 heikki.linnakangas@i 526 :GNC 16764 : arrayP->pgprocnos[index] = GetNumberFromPGProc(proc);
1038 andres@anarazel.de 527 :CBC 16764 : proc->pgxactoff = index;
1339 528 : 16764 : ProcGlobal->xids[index] = proc->xid;
529 : 16764 : ProcGlobal->subxidStates[index] = proc->subxidStatus;
1245 alvherre@alvh.no-ip. 530 : 16764 : ProcGlobal->statusFlags[index] = proc->statusFlags;
531 : :
6905 tgl@sss.pgh.pa.us 532 : 16764 : arrayP->numProcs++;
533 : :
534 : : /* adjust pgxactoff for all following PGPROCs */
1038 andres@anarazel.de 535 : 16764 : index++;
1339 536 [ + + ]: 46184 : for (; index < arrayP->numProcs; index++)
537 : : {
1038 538 : 29420 : int procno = arrayP->pgprocnos[index];
539 : :
540 [ + - - + ]: 29420 : Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
541 [ - + ]: 29420 : Assert(allProcs[procno].pgxactoff == index - 1);
542 : :
543 : 29420 : allProcs[procno].pgxactoff = index;
544 : : }
545 : :
546 : : /*
547 : : * Release in reversed acquisition order, to reduce frequency of having to
548 : : * wait for XidGenLock while holding ProcArrayLock.
549 : : */
1339 550 : 16764 : LWLockRelease(XidGenLock);
6905 tgl@sss.pgh.pa.us 551 : 16764 : LWLockRelease(ProcArrayLock);
552 : 16764 : }
553 : :
554 : : /*
555 : : * Remove the specified PGPROC from the shared array.
556 : : *
557 : : * When latestXid is a valid XID, we are removing a live 2PC gxact from the
558 : : * array, and thus causing it to appear as "not running" anymore. In this
559 : : * case we must advance latestCompletedXid. (This is essentially the same
560 : : * as ProcArrayEndTransaction followed by removal of the PGPROC, but we take
561 : : * the ProcArrayLock only once, and don't damage the content of the PGPROC;
562 : : * twophase.c depends on the latter.)
563 : : */
564 : : void
6063 565 : 16181 : ProcArrayRemove(PGPROC *proc, TransactionId latestXid)
566 : : {
6905 567 : 16181 : ProcArrayStruct *arrayP = procArray;
568 : : int myoff;
569 : : int movecount;
570 : :
571 : : #ifdef XIDCACHE_DEBUG
572 : : /* dump stats at backend shutdown, but not prepared-xact end */
573 : : if (proc->pid != 0)
574 : : DisplayXidCache();
575 : : #endif
576 : :
577 : : /* See ProcGlobal comment explaining why both locks are held */
578 : 16181 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1339 andres@anarazel.de 579 : 16181 : LWLockAcquire(XidGenLock, LW_EXCLUSIVE);
580 : :
1038 581 : 16181 : myoff = proc->pgxactoff;
582 : :
583 [ + - - + ]: 16181 : Assert(myoff >= 0 && myoff < arrayP->numProcs);
584 [ - + ]: 16181 : Assert(ProcGlobal->allProcs[arrayP->pgprocnos[myoff]].pgxactoff == myoff);
585 : :
6063 tgl@sss.pgh.pa.us 586 [ + + ]: 16181 : if (TransactionIdIsValid(latestXid))
587 : : {
1038 andres@anarazel.de 588 [ - + ]: 395 : Assert(TransactionIdIsValid(ProcGlobal->xids[myoff]));
589 : :
590 : : /* Advance global latestCompletedXid while holding the lock */
1342 591 : 395 : MaintainLatestCompletedXid(latestXid);
592 : :
593 : : /* Same with xactCompletionCount */
128 heikki.linnakangas@i 594 :GNC 395 : TransamVariables->xactCompletionCount++;
595 : :
1038 andres@anarazel.de 596 :CBC 395 : ProcGlobal->xids[myoff] = InvalidTransactionId;
597 : 395 : ProcGlobal->subxidStates[myoff].overflowed = false;
598 : 395 : ProcGlobal->subxidStates[myoff].count = 0;
599 : : }
600 : : else
601 : : {
602 : : /* Shouldn't be trying to remove a live transaction here */
603 [ - + ]: 15786 : Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
604 : : }
605 : :
606 [ - + ]: 16181 : Assert(!TransactionIdIsValid(ProcGlobal->xids[myoff]));
607 [ - + ]: 16181 : Assert(ProcGlobal->subxidStates[myoff].count == 0);
608 [ - + ]: 16181 : Assert(ProcGlobal->subxidStates[myoff].overflowed == false);
609 : :
610 : 16181 : ProcGlobal->statusFlags[myoff] = 0;
611 : :
612 : : /* Keep the PGPROC array sorted. See notes above */
613 : 16181 : movecount = arrayP->numProcs - myoff - 1;
614 : 16181 : memmove(&arrayP->pgprocnos[myoff],
615 : 16181 : &arrayP->pgprocnos[myoff + 1],
616 : : movecount * sizeof(*arrayP->pgprocnos));
617 : 16181 : memmove(&ProcGlobal->xids[myoff],
618 : 16181 : &ProcGlobal->xids[myoff + 1],
619 : : movecount * sizeof(*ProcGlobal->xids));
620 : 16181 : memmove(&ProcGlobal->subxidStates[myoff],
621 : 16181 : &ProcGlobal->subxidStates[myoff + 1],
622 : : movecount * sizeof(*ProcGlobal->subxidStates));
623 : 16181 : memmove(&ProcGlobal->statusFlags[myoff],
624 : 16181 : &ProcGlobal->statusFlags[myoff + 1],
625 : : movecount * sizeof(*ProcGlobal->statusFlags));
626 : :
627 : 16181 : arrayP->pgprocnos[arrayP->numProcs - 1] = -1; /* for debugging */
628 : 16181 : arrayP->numProcs--;
629 : :
630 : : /*
631 : : * Adjust pgxactoff of following procs for removed PGPROC (note that
632 : : * numProcs already has been decremented).
633 : : */
634 [ + + ]: 47937 : for (int index = myoff; index < arrayP->numProcs; index++)
635 : : {
636 : 31756 : int procno = arrayP->pgprocnos[index];
637 : :
638 [ + - - + ]: 31756 : Assert(procno >= 0 && procno < (arrayP->maxProcs + NUM_AUXILIARY_PROCS));
639 [ - + ]: 31756 : Assert(allProcs[procno].pgxactoff - 1 == index);
640 : :
641 : 31756 : allProcs[procno].pgxactoff = index;
642 : : }
643 : :
644 : : /*
645 : : * Release in reversed acquisition order, to reduce frequency of having to
646 : : * wait for XidGenLock while holding ProcArrayLock.
647 : : */
1339 648 : 16181 : LWLockRelease(XidGenLock);
6905 tgl@sss.pgh.pa.us 649 : 16181 : LWLockRelease(ProcArrayLock);
650 : 16181 : }
651 : :
652 : :
653 : : /*
654 : : * ProcArrayEndTransaction -- mark a transaction as no longer running
655 : : *
656 : : * This is used interchangeably for commit and abort cases. The transaction
657 : : * commit/abort must already be reported to WAL and pg_xact.
658 : : *
659 : : * proc is currently always MyProc, but we pass it explicitly for flexibility.
660 : : * latestXid is the latest Xid among the transaction's main XID and
661 : : * subtransactions, or InvalidTransactionId if it has no XID. (We must ask
662 : : * the caller to pass latestXid, instead of computing it from the PGPROC's
663 : : * contents, because the subxid information in the PGPROC might be
664 : : * incomplete.)
665 : : */
666 : : void
6063 667 : 432521 : ProcArrayEndTransaction(PGPROC *proc, TransactionId latestXid)
668 : : {
669 [ + + ]: 432521 : if (TransactionIdIsValid(latestXid))
670 : : {
671 : : /*
672 : : * We must lock ProcArrayLock while clearing our advertised XID, so
673 : : * that we do not exit the set of "running" transactions while someone
674 : : * else is taking a snapshot. See discussion in
675 : : * src/backend/access/transam/README.
676 : : */
1339 andres@anarazel.de 677 [ - + ]: 114251 : Assert(TransactionIdIsValid(proc->xid));
678 : :
679 : : /*
680 : : * If we can immediately acquire ProcArrayLock, we clear our own XID
681 : : * and release the lock. If not, use group XID clearing to improve
682 : : * efficiency.
683 : : */
3174 rhaas@postgresql.org 684 [ + + ]: 114251 : if (LWLockConditionalAcquire(ProcArrayLock, LW_EXCLUSIVE))
685 : : {
1339 andres@anarazel.de 686 : 113819 : ProcArrayEndTransactionInternal(proc, latestXid);
3174 rhaas@postgresql.org 687 : 113819 : LWLockRelease(ProcArrayLock);
688 : : }
689 : : else
690 : 432 : ProcArrayGroupClearXid(proc, latestXid);
691 : : }
692 : : else
693 : : {
694 : : /*
695 : : * If we have no XID, we don't need to lock, since we won't affect
696 : : * anyone else's calculation of a snapshot. We might change their
697 : : * estimate of global xmin, but that's OK.
698 : : */
1339 andres@anarazel.de 699 [ - + ]: 318270 : Assert(!TransactionIdIsValid(proc->xid));
700 [ - + ]: 318270 : Assert(proc->subxidStatus.count == 0);
701 [ - + ]: 318270 : Assert(!proc->subxidStatus.overflowed);
702 : :
42 heikki.linnakangas@i 703 :GNC 318270 : proc->vxid.lxid = InvalidLocalTransactionId;
1340 andres@anarazel.de 704 :CBC 318270 : proc->xmin = InvalidTransactionId;
705 : :
706 : : /* be sure this is cleared in abort */
737 rhaas@postgresql.org 707 : 318270 : proc->delayChkptFlags = 0;
708 : :
5202 simon@2ndQuadrant.co 709 : 318270 : proc->recoveryConflictPending = false;
710 : :
711 : : /* must be cleared with xid/xmin: */
712 : : /* avoid unnecessarily dirtying shared cachelines */
1245 alvherre@alvh.no-ip. 713 [ + + ]: 318270 : if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
714 : : {
1369 andres@anarazel.de 715 [ - + ]: 84178 : Assert(!LWLockHeldByMe(ProcArrayLock));
1235 alvherre@alvh.no-ip. 716 : 84178 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1245 717 [ - + ]: 84178 : Assert(proc->statusFlags == ProcGlobal->statusFlags[proc->pgxactoff]);
718 : 84178 : proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
719 : 84178 : ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
1369 andres@anarazel.de 720 : 84178 : LWLockRelease(ProcArrayLock);
721 : : }
722 : : }
6063 tgl@sss.pgh.pa.us 723 : 432521 : }
724 : :
725 : : /*
726 : : * Mark a write transaction as no longer running.
727 : : *
728 : : * We don't do any locking here; caller must handle that.
729 : : */
730 : : static inline void
1339 andres@anarazel.de 731 : 114251 : ProcArrayEndTransactionInternal(PGPROC *proc, TransactionId latestXid)
732 : : {
941 fujii@postgresql.org 733 : 114251 : int pgxactoff = proc->pgxactoff;
734 : :
735 : : /*
736 : : * Note: we need exclusive lock here because we're going to change other
737 : : * processes' PGPROC entries.
738 : : */
1243 alvherre@alvh.no-ip. 739 [ - + ]: 114251 : Assert(LWLockHeldByMeInMode(ProcArrayLock, LW_EXCLUSIVE));
1339 andres@anarazel.de 740 [ - + ]: 114251 : Assert(TransactionIdIsValid(ProcGlobal->xids[pgxactoff]));
741 [ - + ]: 114251 : Assert(ProcGlobal->xids[pgxactoff] == proc->xid);
742 : :
743 : 114251 : ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
744 : 114251 : proc->xid = InvalidTransactionId;
42 heikki.linnakangas@i 745 :GNC 114251 : proc->vxid.lxid = InvalidLocalTransactionId;
1340 andres@anarazel.de 746 :CBC 114251 : proc->xmin = InvalidTransactionId;
747 : :
748 : : /* be sure this is cleared in abort */
737 rhaas@postgresql.org 749 : 114251 : proc->delayChkptFlags = 0;
750 : :
3174 751 : 114251 : proc->recoveryConflictPending = false;
752 : :
753 : : /* must be cleared with xid/xmin: */
754 : : /* avoid unnecessarily dirtying shared cachelines */
1245 alvherre@alvh.no-ip. 755 [ + + ]: 114251 : if (proc->statusFlags & PROC_VACUUM_STATE_MASK)
756 : : {
757 : 614 : proc->statusFlags &= ~PROC_VACUUM_STATE_MASK;
758 : 614 : ProcGlobal->statusFlags[proc->pgxactoff] = proc->statusFlags;
759 : : }
760 : :
761 : : /* Clear the subtransaction-XID cache too while holding the lock */
1339 andres@anarazel.de 762 [ + - - + ]: 114251 : Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
763 : : ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
764 [ + + - + ]: 114251 : if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
765 : : {
766 : 572 : ProcGlobal->subxidStates[pgxactoff].count = 0;
767 : 572 : ProcGlobal->subxidStates[pgxactoff].overflowed = false;
768 : 572 : proc->subxidStatus.count = 0;
769 : 572 : proc->subxidStatus.overflowed = false;
770 : : }
771 : :
772 : : /* Also advance global latestCompletedXid while holding the lock */
1342 773 : 114251 : MaintainLatestCompletedXid(latestXid);
774 : :
775 : : /* Same with xactCompletionCount */
128 heikki.linnakangas@i 776 :GNC 114251 : TransamVariables->xactCompletionCount++;
3174 rhaas@postgresql.org 777 :CBC 114251 : }
778 : :
779 : : /*
780 : : * ProcArrayGroupClearXid -- group XID clearing
781 : : *
782 : : * When we cannot immediately acquire ProcArrayLock in exclusive mode at
783 : : * commit time, add ourselves to a list of processes that need their XIDs
784 : : * cleared. The first process to add itself to the list will acquire
785 : : * ProcArrayLock in exclusive mode and perform ProcArrayEndTransactionInternal
786 : : * on behalf of all group members. This avoids a great deal of contention
787 : : * around ProcArrayLock when many processes are trying to commit at once,
788 : : * since the lock need not be repeatedly handed off from one committing
789 : : * process to the next.
790 : : */
791 : : static void
792 : 432 : ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
793 : : {
52 heikki.linnakangas@i 794 :GNC 432 : int pgprocno = GetNumberFromPGProc(proc);
1983 andres@anarazel.de 795 :CBC 432 : PROC_HDR *procglobal = ProcGlobal;
796 : : uint32 nextidx;
797 : : uint32 wakeidx;
798 : :
799 : : /* We should definitely have an XID to clear. */
1339 800 [ - + ]: 432 : Assert(TransactionIdIsValid(proc->xid));
801 : :
802 : : /* Add ourselves to the list of processes needing a group XID clear. */
2985 rhaas@postgresql.org 803 : 432 : proc->procArrayGroupMember = true;
804 : 432 : proc->procArrayGroupMemberXid = latestXid;
1640 noah@leadboat.com 805 : 432 : nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
806 : : while (true)
807 : : {
2985 rhaas@postgresql.org 808 : 435 : pg_atomic_write_u32(&proc->procArrayGroupNext, nextidx);
809 : :
810 [ + + ]: 435 : if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
811 : : &nextidx,
812 : : (uint32) pgprocno))
3174 813 : 432 : break;
814 : : }
815 : :
816 : : /*
817 : : * If the list was not empty, the leader will clear our XID. It is
818 : : * impossible to have followers without a leader because the first process
819 : : * that has added itself to the list will always have nextidx as
820 : : * INVALID_PROC_NUMBER.
821 : : */
42 heikki.linnakangas@i 822 [ + + ]:GNC 432 : if (nextidx != INVALID_PROC_NUMBER)
823 : : {
2656 rhaas@postgresql.org 824 :CBC 13 : int extraWaits = 0;
825 : :
826 : : /* Sleep until the leader clears our XID. */
2564 827 : 13 : pgstat_report_wait_start(WAIT_EVENT_PROCARRAY_GROUP_UPDATE);
828 : : for (;;)
829 : : {
830 : : /* acts as a read barrier */
2680 tgl@sss.pgh.pa.us 831 : 13 : PGSemaphoreLock(proc->sem);
2985 rhaas@postgresql.org 832 [ + - ]: 13 : if (!proc->procArrayGroupMember)
3146 833 : 13 : break;
3146 rhaas@postgresql.org 834 :UBC 0 : extraWaits++;
835 : : }
2564 rhaas@postgresql.org 836 :CBC 13 : pgstat_report_wait_end();
837 : :
42 heikki.linnakangas@i 838 [ - + ]:GNC 13 : Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PROC_NUMBER);
839 : :
840 : : /* Fix semaphore count for any absorbed wakeups */
3174 rhaas@postgresql.org 841 [ - + ]:CBC 13 : while (extraWaits-- > 0)
2680 tgl@sss.pgh.pa.us 842 :UBC 0 : PGSemaphoreUnlock(proc->sem);
3174 rhaas@postgresql.org 843 :CBC 13 : return;
844 : : }
845 : :
846 : : /* We are the leader. Acquire the lock on behalf of everyone. */
847 : 419 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
848 : :
849 : : /*
850 : : * Now that we've got the lock, clear the list of processes waiting for
851 : : * group XID clearing, saving a pointer to the head of the list. Trying
852 : : * to pop elements one at a time could lead to an ABA problem.
853 : : */
2031 akorotkov@postgresql 854 : 419 : nextidx = pg_atomic_exchange_u32(&procglobal->procArrayGroupFirst,
855 : : INVALID_PROC_NUMBER);
856 : :
857 : : /* Remember head of list so we can perform wakeups after dropping lock. */
3174 rhaas@postgresql.org 858 : 419 : wakeidx = nextidx;
859 : :
860 : : /* Walk the list and clear all XIDs. */
42 heikki.linnakangas@i 861 [ + + ]:GNC 851 : while (nextidx != INVALID_PROC_NUMBER)
862 : : {
941 fujii@postgresql.org 863 :CBC 432 : PGPROC *nextproc = &allProcs[nextidx];
864 : :
865 : 432 : ProcArrayEndTransactionInternal(nextproc, nextproc->procArrayGroupMemberXid);
866 : :
867 : : /* Move to next proc in list. */
868 : 432 : nextidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
869 : : }
870 : :
871 : : /* We're done with the lock now. */
3174 rhaas@postgresql.org 872 : 419 : LWLockRelease(ProcArrayLock);
873 : :
874 : : /*
875 : : * Now that we've released the lock, go back and wake everybody up. We
876 : : * don't do this under the lock so as to keep lock hold times to a
877 : : * minimum. The system calls we need to perform to wake other processes
878 : : * up are probably much slower than the simple memory writes we did while
879 : : * holding the lock.
880 : : */
42 heikki.linnakangas@i 881 [ + + ]:GNC 851 : while (wakeidx != INVALID_PROC_NUMBER)
882 : : {
941 fujii@postgresql.org 883 :CBC 432 : PGPROC *nextproc = &allProcs[wakeidx];
884 : :
885 : 432 : wakeidx = pg_atomic_read_u32(&nextproc->procArrayGroupNext);
42 heikki.linnakangas@i 886 :GNC 432 : pg_atomic_write_u32(&nextproc->procArrayGroupNext, INVALID_PROC_NUMBER);
887 : :
888 : : /* ensure all previous writes are visible before follower continues. */
3146 rhaas@postgresql.org 889 :CBC 432 : pg_write_barrier();
890 : :
941 fujii@postgresql.org 891 : 432 : nextproc->procArrayGroupMember = false;
892 : :
893 [ + + ]: 432 : if (nextproc != MyProc)
894 : 13 : PGSemaphoreUnlock(nextproc->sem);
895 : : }
896 : : }
897 : :
898 : : /*
899 : : * ProcArrayClearTransaction -- clear the transaction fields
900 : : *
901 : : * This is used after successfully preparing a 2-phase transaction. We are
902 : : * not actually reporting the transaction's XID as no longer running --- it
903 : : * will still appear as running because the 2PC's gxact is in the ProcArray
904 : : * too. We just have to clear out our own PGPROC.
905 : : */
906 : : void
6063 tgl@sss.pgh.pa.us 907 : 391 : ProcArrayClearTransaction(PGPROC *proc)
908 : : {
909 : : int pgxactoff;
910 : :
911 : : /*
912 : : * Currently we need to lock ProcArrayLock exclusively here, as we
913 : : * increment xactCompletionCount below. We also need it at least in shared
914 : : * mode for pgproc->pgxactoff to stay the same below.
915 : : *
916 : : * We could however, as this action does not actually change anyone's view
917 : : * of the set of running XIDs (our entry is duplicate with the gxact that
918 : : * has already been inserted into the ProcArray), lower the lock level to
919 : : * shared if we were to make xactCompletionCount an atomic variable. But
920 : : * that doesn't seem worth it currently, as a 2PC commit is heavyweight
921 : : * enough for this not to be the bottleneck. If it ever becomes a
922 : : * bottleneck it may also be worth considering to combine this with the
923 : : * subsequent ProcArrayRemove()
924 : : */
1334 andres@anarazel.de 925 : 391 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
926 : :
1339 927 : 391 : pgxactoff = proc->pgxactoff;
928 : :
929 : 391 : ProcGlobal->xids[pgxactoff] = InvalidTransactionId;
930 : 391 : proc->xid = InvalidTransactionId;
931 : :
42 heikki.linnakangas@i 932 :GNC 391 : proc->vxid.lxid = InvalidLocalTransactionId;
1340 andres@anarazel.de 933 :CBC 391 : proc->xmin = InvalidTransactionId;
5202 simon@2ndQuadrant.co 934 : 391 : proc->recoveryConflictPending = false;
935 : :
1245 alvherre@alvh.no-ip. 936 [ - + ]: 391 : Assert(!(proc->statusFlags & PROC_VACUUM_STATE_MASK));
737 rhaas@postgresql.org 937 [ - + ]: 391 : Assert(!proc->delayChkptFlags);
938 : :
939 : : /*
940 : : * Need to increment completion count even though transaction hasn't
941 : : * really committed yet. The reason for that is that GetSnapshotData()
942 : : * omits the xid of the current transaction, thus without the increment we
943 : : * otherwise could end up reusing the snapshot later. Which would be bad,
944 : : * because it might not count the prepared transaction as running.
945 : : */
128 heikki.linnakangas@i 946 :GNC 391 : TransamVariables->xactCompletionCount++;
947 : :
948 : : /* Clear the subtransaction-XID cache too */
1339 andres@anarazel.de 949 [ + - - + ]:CBC 391 : Assert(ProcGlobal->subxidStates[pgxactoff].count == proc->subxidStatus.count &&
950 : : ProcGlobal->subxidStates[pgxactoff].overflowed == proc->subxidStatus.overflowed);
951 [ + + - + ]: 391 : if (proc->subxidStatus.count > 0 || proc->subxidStatus.overflowed)
952 : : {
953 : 150 : ProcGlobal->subxidStates[pgxactoff].count = 0;
954 : 150 : ProcGlobal->subxidStates[pgxactoff].overflowed = false;
955 : 150 : proc->subxidStatus.count = 0;
956 : 150 : proc->subxidStatus.overflowed = false;
957 : : }
958 : :
959 : 391 : LWLockRelease(ProcArrayLock);
6063 tgl@sss.pgh.pa.us 960 : 391 : }
961 : :
962 : : /*
963 : : * Update TransamVariables->latestCompletedXid to point to latestXid if
964 : : * currently older.
965 : : */
966 : : static void
1342 andres@anarazel.de 967 : 115294 : MaintainLatestCompletedXid(TransactionId latestXid)
968 : : {
128 heikki.linnakangas@i 969 :GNC 115294 : FullTransactionId cur_latest = TransamVariables->latestCompletedXid;
970 : :
1342 andres@anarazel.de 971 [ - + ]:CBC 115294 : Assert(FullTransactionIdIsValid(cur_latest));
972 [ - + ]: 115294 : Assert(!RecoveryInProgress());
973 [ - + ]: 115294 : Assert(LWLockHeldByMe(ProcArrayLock));
974 : :
975 [ + + ]: 115294 : if (TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
976 : : {
128 heikki.linnakangas@i 977 :GNC 101636 : TransamVariables->latestCompletedXid =
1342 andres@anarazel.de 978 :CBC 101636 : FullXidRelativeTo(cur_latest, latestXid);
979 : : }
980 : :
981 [ + + - + ]: 115294 : Assert(IsBootstrapProcessingMode() ||
982 : : FullTransactionIdIsNormal(TransamVariables->latestCompletedXid));
983 : 115294 : }
984 : :
985 : : /*
986 : : * Same as MaintainLatestCompletedXid, except for use during WAL replay.
987 : : */
988 : : static void
989 : 20360 : MaintainLatestCompletedXidRecovery(TransactionId latestXid)
990 : : {
128 heikki.linnakangas@i 991 :GNC 20360 : FullTransactionId cur_latest = TransamVariables->latestCompletedXid;
992 : : FullTransactionId rel;
993 : :
1342 andres@anarazel.de 994 [ - + - - ]:CBC 20360 : Assert(AmStartupProcess() || !IsUnderPostmaster);
995 [ - + ]: 20360 : Assert(LWLockHeldByMe(ProcArrayLock));
996 : :
997 : : /*
998 : : * Need a FullTransactionId to compare latestXid with. Can't rely on
999 : : * latestCompletedXid to be initialized in recovery. But in recovery it's
1000 : : * safe to access nextXid without a lock for the startup process.
1001 : : */
128 heikki.linnakangas@i 1002 :GNC 20360 : rel = TransamVariables->nextXid;
1003 [ - + ]: 20360 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
1004 : :
1342 andres@anarazel.de 1005 [ + + + + ]:CBC 40582 : if (!FullTransactionIdIsValid(cur_latest) ||
1006 : 20222 : TransactionIdPrecedes(XidFromFullTransactionId(cur_latest), latestXid))
1007 : : {
128 heikki.linnakangas@i 1008 :GNC 16151 : TransamVariables->latestCompletedXid =
1342 andres@anarazel.de 1009 :CBC 16151 : FullXidRelativeTo(rel, latestXid);
1010 : : }
1011 : :
128 heikki.linnakangas@i 1012 [ - + ]:GNC 20360 : Assert(FullTransactionIdIsNormal(TransamVariables->latestCompletedXid));
1342 andres@anarazel.de 1013 :CBC 20360 : }
1014 : :
1015 : : /*
1016 : : * ProcArrayInitRecovery -- initialize recovery xid mgmt environment
1017 : : *
1018 : : * Remember up to where the startup process initialized the CLOG and subtrans
1019 : : * so we can ensure it's initialized gaplessly up to the point where necessary
1020 : : * while in recovery.
1021 : : */
1022 : : void
3948 simon@2ndQuadrant.co 1023 : 138 : ProcArrayInitRecovery(TransactionId initializedUptoXID)
1024 : : {
1025 [ - + ]: 138 : Assert(standbyState == STANDBY_INITIALIZED);
1026 [ - + ]: 138 : Assert(TransactionIdIsNormal(initializedUptoXID));
1027 : :
1028 : : /*
1029 : : * we set latestObservedXid to the xid SUBTRANS has been initialized up
1030 : : * to, so we can extend it from that point onwards in
1031 : : * RecordKnownAssignedTransactionIds, and when we get consistent in
1032 : : * ProcArrayApplyRecoveryInfo().
1033 : : */
1034 : 138 : latestObservedXid = initializedUptoXID;
1035 [ - + ]: 138 : TransactionIdRetreat(latestObservedXid);
1036 : 138 : }
1037 : :
1038 : : /*
1039 : : * ProcArrayApplyRecoveryInfo -- apply recovery info about xids
1040 : : *
1041 : : * Takes us through 3 states: Initialized, Pending and Ready.
1042 : : * Normal case is to go all the way to Ready straight away, though there
1043 : : * are atypical cases where we need to take it in steps.
1044 : : *
1045 : : * Use the data about running transactions on the primary to create the initial
1046 : : * state of KnownAssignedXids. We also use these records to regularly prune
1047 : : * KnownAssignedXids because we know it is possible that some transactions
1048 : : * with FATAL errors fail to write abort records, which could cause eventual
1049 : : * overflow.
1050 : : *
1051 : : * See comments for LogStandbySnapshot().
1052 : : */
1053 : : void
5230 1054 : 400 : ProcArrayApplyRecoveryInfo(RunningTransactions running)
1055 : : {
1056 : : TransactionId *xids;
1057 : : TransactionId advanceNextXid;
1058 : : int nxids;
1059 : : int i;
1060 : :
1061 [ - + ]: 400 : Assert(standbyState >= STANDBY_INITIALIZED);
5084 1062 [ - + ]: 400 : Assert(TransactionIdIsValid(running->nextXid));
1063 [ - + ]: 400 : Assert(TransactionIdIsValid(running->oldestRunningXid));
1064 [ - + ]: 400 : Assert(TransactionIdIsNormal(running->latestCompletedXid));
1065 : :
1066 : : /*
1067 : : * Remove stale transactions, if any.
1068 : : */
5230 1069 : 400 : ExpireOldKnownAssignedTransactionIds(running->oldestRunningXid);
1070 : :
1071 : : /*
1072 : : * Adjust TransamVariables->nextXid before StandbyReleaseOldLocks(),
1073 : : * because we will need it up to date for accessing two-phase transactions
1074 : : * in StandbyReleaseOldLocks().
1075 : : */
86 akorotkov@postgresql 1076 :GNC 400 : advanceNextXid = running->nextXid;
1077 [ - + ]: 400 : TransactionIdRetreat(advanceNextXid);
1078 : 400 : AdvanceNextFullTransactionIdPastXid(advanceNextXid);
1079 [ - + ]: 400 : Assert(FullTransactionIdIsValid(TransamVariables->nextXid));
1080 : :
1081 : : /*
1082 : : * Remove stale locks, if any.
1083 : : */
2129 simon@2ndQuadrant.co 1084 :CBC 400 : StandbyReleaseOldLocks(running->oldestRunningXid);
1085 : :
1086 : : /*
1087 : : * If our snapshot is already valid, nothing else to do...
1088 : : */
5230 1089 [ + + ]: 400 : if (standbyState == STANDBY_SNAPSHOT_READY)
1090 : 262 : return;
1091 : :
1092 : : /*
1093 : : * If our initial RunningTransactionsData had an overflowed snapshot then
1094 : : * we knew we were missing some subxids from our snapshot. If we continue
1095 : : * to see overflowed snapshots then we might never be able to start up, so
1096 : : * we make another test to see if our snapshot is now valid. We know that
1097 : : * the missing subxids are equal to or earlier than nextXid. After we
1098 : : * initialise we continue to apply changes during recovery, so once the
1099 : : * oldestRunningXid is later than the nextXid from the initial snapshot we
1100 : : * know that we no longer have missing information and can mark the
1101 : : * snapshot as valid.
1102 : : */
1103 [ - + ]: 138 : if (standbyState == STANDBY_SNAPSHOT_PENDING)
1104 : : {
1105 : : /*
1106 : : * If the snapshot isn't overflowed or if its empty we can reset our
1107 : : * pending state and use this snapshot instead.
1108 : : */
4547 simon@2ndQuadrant.co 1109 [ # # # # ]:UBC 0 : if (!running->subxid_overflow || running->xcnt == 0)
1110 : : {
1111 : : /*
1112 : : * If we have already collected known assigned xids, we need to
1113 : : * throw them away before we apply the recovery snapshot.
1114 : : */
4328 1115 : 0 : KnownAssignedXidsReset();
4547 1116 : 0 : standbyState = STANDBY_INITIALIZED;
1117 : : }
1118 : : else
1119 : : {
1120 [ # # ]: 0 : if (TransactionIdPrecedes(standbySnapshotPendingXmin,
1121 : : running->oldestRunningXid))
1122 : : {
1123 : 0 : standbyState = STANDBY_SNAPSHOT_READY;
125 michael@paquier.xyz 1124 [ # # ]:UNC 0 : elog(DEBUG1,
1125 : : "recovery snapshots are now enabled");
1126 : : }
1127 : : else
1128 [ # # ]: 0 : elog(DEBUG1,
1129 : : "recovery snapshot waiting for non-overflowed snapshot or "
1130 : : "until oldest active xid on standby is at least %u (now %u)",
1131 : : standbySnapshotPendingXmin,
1132 : : running->oldestRunningXid);
4547 simon@2ndQuadrant.co 1133 :UBC 0 : return;
1134 : : }
1135 : : }
1136 : :
5085 simon@2ndQuadrant.co 1137 [ - + ]:CBC 138 : Assert(standbyState == STANDBY_INITIALIZED);
1138 : :
1139 : : /*
1140 : : * NB: this can be reached at least twice, so make sure new code can deal
1141 : : * with that.
1142 : : */
1143 : :
1144 : : /*
1145 : : * Nobody else is running yet, but take locks anyhow
1146 : : */
1147 : 138 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1148 : :
1149 : : /*
1150 : : * KnownAssignedXids is sorted so we cannot just add the xids, we have to
1151 : : * sort them first.
1152 : : *
1153 : : * Some of the new xids are top-level xids and some are subtransactions.
1154 : : * We don't call SubTransSetParent because it doesn't matter yet. If we
1155 : : * aren't overflowed then all xids will fit in snapshot and so we don't
1156 : : * need subtrans. If we later overflow, an xid assignment record will add
1157 : : * xids to subtrans. If RunningTransactionsData is overflowed then we
1158 : : * don't have enough information to correctly update subtrans anyway.
1159 : : */
1160 : :
1161 : : /*
1162 : : * Allocate a temporary array to avoid modifying the array passed as
1163 : : * argument.
1164 : : */
4151 1165 : 138 : xids = palloc(sizeof(TransactionId) * (running->xcnt + running->subxcnt));
1166 : :
1167 : : /*
1168 : : * Add to the temp array any xids which have not already completed.
1169 : : */
4877 heikki.linnakangas@i 1170 : 138 : nxids = 0;
4151 simon@2ndQuadrant.co 1171 [ + + ]: 146 : for (i = 0; i < running->xcnt + running->subxcnt; i++)
1172 : : {
5085 1173 : 8 : TransactionId xid = running->xids[i];
1174 : :
1175 : : /*
1176 : : * The running-xacts snapshot can contain xids that were still visible
1177 : : * in the procarray when the snapshot was taken, but were already
1178 : : * WAL-logged as completed. They're not running anymore, so ignore
1179 : : * them.
1180 : : */
5230 1181 [ + + - + ]: 8 : if (TransactionIdDidCommit(xid) || TransactionIdDidAbort(xid))
1182 : 3 : continue;
1183 : :
5085 1184 : 5 : xids[nxids++] = xid;
1185 : : }
1186 : :
1187 [ + + ]: 138 : if (nxids > 0)
1188 : : {
4328 1189 [ - + ]: 5 : if (procArray->numKnownAssignedXids != 0)
1190 : : {
4328 simon@2ndQuadrant.co 1191 :UBC 0 : LWLockRelease(ProcArrayLock);
1192 [ # # ]: 0 : elog(ERROR, "KnownAssignedXids is not empty");
1193 : : }
1194 : :
1195 : : /*
1196 : : * Sort the array so that we can add them safely into
1197 : : * KnownAssignedXids.
1198 : : *
1199 : : * We have to sort them logically, because in KnownAssignedXidsAdd we
1200 : : * call TransactionIdFollowsOrEquals and so on. But we know these XIDs
1201 : : * come from RUNNING_XACTS, which means there are only normal XIDs
1202 : : * from the same epoch, so this is safe.
1203 : : */
808 tomas.vondra@postgre 1204 :CBC 5 : qsort(xids, nxids, sizeof(TransactionId), xidLogicalComparator);
1205 : :
1206 : : /*
1207 : : * Add the sorted snapshot into KnownAssignedXids. The running-xacts
1208 : : * snapshot may include duplicated xids because of prepared
1209 : : * transactions, so ignore them.
1210 : : */
5085 simon@2ndQuadrant.co 1211 [ + + ]: 10 : for (i = 0; i < nxids; i++)
1212 : : {
2009 michael@paquier.xyz 1213 [ - + - - ]: 5 : if (i > 0 && TransactionIdEquals(xids[i - 1], xids[i]))
1214 : : {
2009 michael@paquier.xyz 1215 [ # # ]:UBC 0 : elog(DEBUG1,
1216 : : "found duplicated transaction %u for KnownAssignedXids insertion",
1217 : : xids[i]);
1218 : 0 : continue;
1219 : : }
4877 heikki.linnakangas@i 1220 :CBC 5 : KnownAssignedXidsAdd(xids[i], xids[i], true);
1221 : : }
1222 : :
125 michael@paquier.xyz 1223 :GNC 5 : KnownAssignedXidsDisplay(DEBUG3);
1224 : : }
1225 : :
5085 simon@2ndQuadrant.co 1226 :CBC 138 : pfree(xids);
1227 : :
1228 : : /*
1229 : : * latestObservedXid is at least set to the point where SUBTRANS was
1230 : : * started up to (cf. ProcArrayInitRecovery()) or to the biggest xid
1231 : : * RecordKnownAssignedTransactionIds() was called for. Initialize
1232 : : * subtrans from thereon, up to nextXid - 1.
1233 : : *
1234 : : * We need to duplicate parts of RecordKnownAssignedTransactionId() here,
1235 : : * because we've just added xids to the known assigned xids machinery that
1236 : : * haven't gone through RecordKnownAssignedTransactionId().
1237 : : */
3948 1238 [ - + ]: 138 : Assert(TransactionIdIsNormal(latestObservedXid));
3796 heikki.linnakangas@i 1239 [ - + ]: 138 : TransactionIdAdvance(latestObservedXid);
3948 simon@2ndQuadrant.co 1240 [ - + ]: 276 : while (TransactionIdPrecedes(latestObservedXid, running->nextXid))
1241 : : {
3948 simon@2ndQuadrant.co 1242 :UBC 0 : ExtendSUBTRANS(latestObservedXid);
1243 [ # # ]: 0 : TransactionIdAdvance(latestObservedXid);
1244 : : }
3631 bruce@momjian.us 1245 [ - + ]:CBC 138 : TransactionIdRetreat(latestObservedXid); /* = running->nextXid - 1 */
1246 : :
1247 : : /* ----------
1248 : : * Now we've got the running xids we need to set the global values that
1249 : : * are used to track snapshots as they evolve further.
1250 : : *
1251 : : * - latestCompletedXid which will be the xmax for snapshots
1252 : : * - lastOverflowedXid which shows whether snapshots overflow
1253 : : * - nextXid
1254 : : *
1255 : : * If the snapshot overflowed, then we still initialise with what we know,
1256 : : * but the recovery snapshot isn't fully valid yet because we know there
1257 : : * are some subxids missing. We don't know the specific subxids that are
1258 : : * missing, so conservatively assume the last one is latestObservedXid.
1259 : : * ----------
1260 : : */
5100 tgl@sss.pgh.pa.us 1261 [ - + ]: 138 : if (running->subxid_overflow)
1262 : : {
5085 simon@2ndQuadrant.co 1263 :UBC 0 : standbyState = STANDBY_SNAPSHOT_PENDING;
1264 : :
1265 : 0 : standbySnapshotPendingXmin = latestObservedXid;
4877 heikki.linnakangas@i 1266 : 0 : procArray->lastOverflowedXid = latestObservedXid;
1267 : : }
1268 : : else
1269 : : {
5085 simon@2ndQuadrant.co 1270 :CBC 138 : standbyState = STANDBY_SNAPSHOT_READY;
1271 : :
1272 : 138 : standbySnapshotPendingXmin = InvalidTransactionId;
1273 : : }
1274 : :
1275 : : /*
1276 : : * If a transaction wrote a commit record in the gap between taking and
1277 : : * logging the snapshot then latestCompletedXid may already be higher than
1278 : : * the value from the snapshot, so check before we use the incoming value.
1279 : : * It also might not yet be set at all.
1280 : : */
1342 andres@anarazel.de 1281 : 138 : MaintainLatestCompletedXidRecovery(running->latestCompletedXid);
1282 : :
1283 : : /*
1284 : : * NB: No need to increment TransamVariables->xactCompletionCount here,
1285 : : * nobody can see it yet.
1286 : : */
1287 : :
4451 tgl@sss.pgh.pa.us 1288 : 138 : LWLockRelease(ProcArrayLock);
1289 : :
125 michael@paquier.xyz 1290 :GNC 138 : KnownAssignedXidsDisplay(DEBUG3);
5230 simon@2ndQuadrant.co 1291 [ + - ]:CBC 138 : if (standbyState == STANDBY_SNAPSHOT_READY)
125 michael@paquier.xyz 1292 [ + + ]:GNC 138 : elog(DEBUG1, "recovery snapshots are now enabled");
1293 : : else
125 michael@paquier.xyz 1294 [ # # ]:UNC 0 : elog(DEBUG1,
1295 : : "recovery snapshot waiting for non-overflowed snapshot or "
1296 : : "until oldest active xid on standby is at least %u (now %u)",
1297 : : standbySnapshotPendingXmin,
1298 : : running->oldestRunningXid);
1299 : : }
1300 : :
1301 : : /*
1302 : : * ProcArrayApplyXidAssignment
1303 : : * Process an XLOG_XACT_ASSIGNMENT WAL record
1304 : : */
1305 : : void
5230 simon@2ndQuadrant.co 1306 :CBC 36 : ProcArrayApplyXidAssignment(TransactionId topxid,
1307 : : int nsubxids, TransactionId *subxids)
1308 : : {
1309 : : TransactionId max_xid;
1310 : : int i;
1311 : :
5085 1312 [ - + ]: 36 : Assert(standbyState >= STANDBY_INITIALIZED);
1313 : :
5230 1314 : 36 : max_xid = TransactionIdLatest(topxid, nsubxids, subxids);
1315 : :
1316 : : /*
1317 : : * Mark all the subtransactions as observed.
1318 : : *
1319 : : * NOTE: This will fail if the subxid contains too many previously
1320 : : * unobserved xids to fit into known-assigned-xids. That shouldn't happen
1321 : : * as the code stands, because xid-assignment records should never contain
1322 : : * more than PGPROC_MAX_CACHED_SUBXIDS entries.
1323 : : */
1324 : 36 : RecordKnownAssignedTransactionIds(max_xid);
1325 : :
1326 : : /*
1327 : : * Notice that we update pg_subtrans with the top-level xid, rather than
1328 : : * the parent xid. This is a difference between normal processing and
1329 : : * recovery, yet is still correct in all cases. The reason is that
1330 : : * subtransaction commit is not marked in clog until commit processing, so
1331 : : * all aborted subtransactions have already been clearly marked in clog.
1332 : : * As a result we are able to refer directly to the top-level
1333 : : * transaction's state rather than skipping through all the intermediate
1334 : : * states in the subtransaction tree. This should be the first time we
1335 : : * have attempted to SubTransSetParent().
1336 : : */
1337 [ + + ]: 2340 : for (i = 0; i < nsubxids; i++)
2544 1338 : 2304 : SubTransSetParent(subxids[i], topxid);
1339 : :
1340 : : /* KnownAssignedXids isn't maintained yet, so we're done for now */
3796 heikki.linnakangas@i 1341 [ - + ]: 36 : if (standbyState == STANDBY_INITIALIZED)
3796 heikki.linnakangas@i 1342 :UBC 0 : return;
1343 : :
1344 : : /*
1345 : : * Uses same locking as transaction commit
1346 : : */
5230 simon@2ndQuadrant.co 1347 :CBC 36 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
1348 : :
1349 : : /*
1350 : : * Remove subxids from known-assigned-xacts.
1351 : : */
5100 tgl@sss.pgh.pa.us 1352 : 36 : KnownAssignedXidsRemoveTree(InvalidTransactionId, nsubxids, subxids);
1353 : :
1354 : : /*
1355 : : * Advance lastOverflowedXid to be at least the last of these subxids.
1356 : : */
5230 simon@2ndQuadrant.co 1357 [ + - ]: 36 : if (TransactionIdPrecedes(procArray->lastOverflowedXid, max_xid))
1358 : 36 : procArray->lastOverflowedXid = max_xid;
1359 : :
1360 : 36 : LWLockRelease(ProcArrayLock);
1361 : : }
1362 : :
1363 : : /*
1364 : : * TransactionIdIsInProgress -- is given transaction running in some backend
1365 : : *
1366 : : * Aside from some shortcuts such as checking RecentXmin and our own Xid,
1367 : : * there are four possibilities for finding a running transaction:
1368 : : *
1369 : : * 1. The given Xid is a main transaction Id. We will find this out cheaply
1370 : : * by looking at ProcGlobal->xids.
1371 : : *
1372 : : * 2. The given Xid is one of the cached subxact Xids in the PGPROC array.
1373 : : * We can find this out cheaply too.
1374 : : *
1375 : : * 3. In Hot Standby mode, we must search the KnownAssignedXids list to see
1376 : : * if the Xid is running on the primary.
1377 : : *
1378 : : * 4. Search the SubTrans tree to find the Xid's topmost parent, and then see
1379 : : * if that is running according to ProcGlobal->xids[] or KnownAssignedXids.
1380 : : * This is the slowest way, but sadly it has to be done always if the others
1381 : : * failed, unless we see that the cached subxact sets are complete (none have
1382 : : * overflowed).
1383 : : *
1384 : : * ProcArrayLock has to be held while we do 1, 2, 3. If we save the top Xids
1385 : : * while doing 1 and 3, we can release the ProcArrayLock while we do 4.
1386 : : * This buys back some concurrency (and we can't retrieve the main Xids from
1387 : : * ProcGlobal->xids[] again anyway; see GetNewTransactionId).
1388 : : */
1389 : : bool
6905 tgl@sss.pgh.pa.us 1390 : 8999296 : TransactionIdIsInProgress(TransactionId xid)
1391 : : {
1392 : : static TransactionId *xids = NULL;
1393 : : static TransactionId *other_xids;
1394 : : XidCacheStatus *other_subxidstates;
6050 1395 : 8999296 : int nxids = 0;
6905 1396 : 8999296 : ProcArrayStruct *arrayP = procArray;
1397 : : TransactionId topxid;
1398 : : TransactionId latestCompletedXid;
1399 : : int mypgxactoff;
1400 : : int numProcs;
1401 : : int j;
1402 : :
1403 : : /*
1404 : : * Don't bother checking a transaction older than RecentXmin; it could not
1405 : : * possibly still be running. (Note: in particular, this guarantees that
1406 : : * we reject InvalidTransactionId, FrozenTransactionId, etc as not
1407 : : * running.)
1408 : : */
1409 [ + + ]: 8999296 : if (TransactionIdPrecedes(xid, RecentXmin))
1410 : : {
1411 : : xc_by_recent_xmin_inc();
1412 : 4162942 : return false;
1413 : : }
1414 : :
1415 : : /*
1416 : : * We may have just checked the status of this transaction, so if it is
1417 : : * already known to be completed, we can fall out without any access to
1418 : : * shared memory.
1419 : : */
657 heikki.linnakangas@i 1420 [ + + ]: 4836354 : if (TransactionIdEquals(cachedXidIsNotInProgress, xid))
1421 : : {
1422 : : xc_by_known_xact_inc();
5878 tgl@sss.pgh.pa.us 1423 : 976081 : return false;
1424 : : }
1425 : :
1426 : : /*
1427 : : * Also, we can handle our own transaction (and subtransactions) without
1428 : : * any access to shared memory.
1429 : : */
6050 1430 [ + + ]: 3860273 : if (TransactionIdIsCurrentTransactionId(xid))
1431 : : {
1432 : : xc_by_my_xact_inc();
1433 : 193780 : return true;
1434 : : }
1435 : :
1436 : : /*
1437 : : * If first time through, get workspace to remember main XIDs in. We
1438 : : * malloc it permanently to avoid repeated palloc/pfree overhead.
1439 : : */
1440 [ + + ]: 3666493 : if (xids == NULL)
1441 : : {
1442 : : /*
1443 : : * In hot standby mode, reserve enough space to hold all xids in the
1444 : : * known-assigned list. If we later finish recovery, we no longer need
1445 : : * the bigger array, but we don't bother to shrink it.
1446 : : */
5100 1447 [ - + ]: 1204 : int maxxids = RecoveryInProgress() ? TOTAL_MAX_CACHED_SUBXIDS : arrayP->maxProcs;
1448 : :
5230 simon@2ndQuadrant.co 1449 : 1204 : xids = (TransactionId *) malloc(maxxids * sizeof(TransactionId));
6050 tgl@sss.pgh.pa.us 1450 [ - + ]: 1204 : if (xids == NULL)
6050 tgl@sss.pgh.pa.us 1451 [ # # ]:UBC 0 : ereport(ERROR,
1452 : : (errcode(ERRCODE_OUT_OF_MEMORY),
1453 : : errmsg("out of memory")));
1454 : : }
1455 : :
1339 andres@anarazel.de 1456 :CBC 3666493 : other_xids = ProcGlobal->xids;
1457 : 3666493 : other_subxidstates = ProcGlobal->subxidStates;
1458 : :
6905 tgl@sss.pgh.pa.us 1459 : 3666493 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1460 : :
1461 : : /*
1462 : : * Now that we have the lock, we can check latestCompletedXid; if the
1463 : : * target Xid is after that, it's surely still running.
1464 : : */
1342 andres@anarazel.de 1465 : 3666493 : latestCompletedXid =
128 heikki.linnakangas@i 1466 :GNC 3666493 : XidFromFullTransactionId(TransamVariables->latestCompletedXid);
1342 andres@anarazel.de 1467 [ + + ]:CBC 3666493 : if (TransactionIdPrecedes(latestCompletedXid, xid))
1468 : : {
6048 tgl@sss.pgh.pa.us 1469 : 3633297 : LWLockRelease(ProcArrayLock);
1470 : : xc_by_latest_xid_inc();
1471 : 3633297 : return true;
1472 : : }
1473 : :
1474 : : /* No shortcuts, gotta grovel through the array */
1339 andres@anarazel.de 1475 : 33196 : mypgxactoff = MyProc->pgxactoff;
1476 : 33196 : numProcs = arrayP->numProcs;
941 fujii@postgresql.org 1477 [ + + ]: 154831 : for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
1478 : : {
1479 : : int pgprocno;
1480 : : PGPROC *proc;
1481 : : TransactionId pxid;
1482 : : int pxids;
1483 : :
1484 : : /* Ignore ourselves --- dealt with it above */
1339 andres@anarazel.de 1485 [ + + ]: 144013 : if (pgxactoff == mypgxactoff)
6050 tgl@sss.pgh.pa.us 1486 : 12136 : continue;
1487 : :
1488 : : /* Fetch xid just once - see GetNewTransactionId */
1339 andres@anarazel.de 1489 : 131877 : pxid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
1490 : :
6905 tgl@sss.pgh.pa.us 1491 [ + + ]: 131877 : if (!TransactionIdIsValid(pxid))
1492 : 74958 : continue;
1493 : :
1494 : : /*
1495 : : * Step 1: check the main Xid
1496 : : */
1497 [ + + ]: 56919 : if (TransactionIdEquals(pxid, xid))
1498 : : {
6050 1499 : 22250 : LWLockRelease(ProcArrayLock);
1500 : : xc_by_main_xid_inc();
1501 : 22250 : return true;
1502 : : }
1503 : :
1504 : : /*
1505 : : * We can ignore main Xids that are younger than the target Xid, since
1506 : : * the target could not possibly be their child.
1507 : : */
6905 1508 [ + + ]: 34669 : if (TransactionIdPrecedes(xid, pxid))
1509 : 17319 : continue;
1510 : :
1511 : : /*
1512 : : * Step 2: check the cached child-Xids arrays
1513 : : */
1339 andres@anarazel.de 1514 : 17350 : pxids = other_subxidstates[pgxactoff].count;
1983 1515 : 17350 : pg_read_barrier(); /* pairs with barrier in GetNewTransactionId() */
1339 1516 : 17350 : pgprocno = arrayP->pgprocnos[pgxactoff];
1517 : 17350 : proc = &allProcs[pgprocno];
1983 1518 [ + + ]: 31967 : for (j = pxids - 1; j >= 0; j--)
1519 : : {
1520 : : /* Fetch xid just once - see GetNewTransactionId */
1521 : 14745 : TransactionId cxid = UINT32_ACCESS_ONCE(proc->subxids.xids[j]);
1522 : :
6905 tgl@sss.pgh.pa.us 1523 [ + + ]: 14745 : if (TransactionIdEquals(cxid, xid))
1524 : : {
6050 1525 : 128 : LWLockRelease(ProcArrayLock);
1526 : : xc_by_child_xid_inc();
1527 : 128 : return true;
1528 : : }
1529 : : }
1530 : :
1531 : : /*
1532 : : * Save the main Xid for step 4. We only need to remember main Xids
1533 : : * that have uncached children. (Note: there is no race condition
1534 : : * here because the overflowed flag cannot be cleared, only set, while
1535 : : * we hold ProcArrayLock. So we can't miss an Xid that we need to
1536 : : * worry about.)
1537 : : */
1339 andres@anarazel.de 1538 [ + + ]: 17222 : if (other_subxidstates[pgxactoff].overflowed)
6905 tgl@sss.pgh.pa.us 1539 : 157 : xids[nxids++] = pxid;
1540 : : }
1541 : :
1542 : : /*
1543 : : * Step 3: in hot standby mode, check the known-assigned-xids list. XIDs
1544 : : * in the list must be treated as running.
1545 : : */
5230 simon@2ndQuadrant.co 1546 [ - + ]: 10818 : if (RecoveryInProgress())
1547 : : {
1548 : : /* none of the PGPROC entries should have XIDs in hot standby mode */
5230 simon@2ndQuadrant.co 1549 [ # # ]:UBC 0 : Assert(nxids == 0);
1550 : :
5100 tgl@sss.pgh.pa.us 1551 [ # # ]: 0 : if (KnownAssignedXidExists(xid))
1552 : : {
5230 simon@2ndQuadrant.co 1553 : 0 : LWLockRelease(ProcArrayLock);
1554 : : xc_by_known_assigned_inc();
1555 : 0 : return true;
1556 : : }
1557 : :
1558 : : /*
1559 : : * If the KnownAssignedXids overflowed, we have to check pg_subtrans
1560 : : * too. Fetch all xids from KnownAssignedXids that are lower than
1561 : : * xid, since if xid is a subtransaction its parent will always have a
1562 : : * lower value. Note we will collect both main and subXIDs here, but
1563 : : * there's no help for it.
1564 : : */
1565 [ # # ]: 0 : if (TransactionIdPrecedesOrEquals(xid, procArray->lastOverflowedXid))
1566 : 0 : nxids = KnownAssignedXidsGet(xids, xid);
1567 : : }
1568 : :
6905 tgl@sss.pgh.pa.us 1569 :CBC 10818 : LWLockRelease(ProcArrayLock);
1570 : :
1571 : : /*
1572 : : * If none of the relevant caches overflowed, we know the Xid is not
1573 : : * running without even looking at pg_subtrans.
1574 : : */
1575 [ + + ]: 10818 : if (nxids == 0)
1576 : : {
1577 : : xc_no_overflow_inc();
657 heikki.linnakangas@i 1578 : 10661 : cachedXidIsNotInProgress = xid;
6050 tgl@sss.pgh.pa.us 1579 : 10661 : return false;
1580 : : }
1581 : :
1582 : : /*
1583 : : * Step 4: have to check pg_subtrans.
1584 : : *
1585 : : * At this point, we know it's either a subtransaction of one of the Xids
1586 : : * in xids[], or it's not running. If it's an already-failed
1587 : : * subtransaction, we want to say "not running" even though its parent may
1588 : : * still be running. So first, check pg_xact to see if it's been aborted.
1589 : : */
1590 : : xc_slow_answer_inc();
1591 : :
6905 1592 [ - + ]: 157 : if (TransactionIdDidAbort(xid))
1593 : : {
657 heikki.linnakangas@i 1594 :UBC 0 : cachedXidIsNotInProgress = xid;
6050 tgl@sss.pgh.pa.us 1595 : 0 : return false;
1596 : : }
1597 : :
1598 : : /*
1599 : : * It isn't aborted, so check whether the transaction tree it belongs to
1600 : : * is still running (or, more precisely, whether it was running when we
1601 : : * held ProcArrayLock).
1602 : : */
6905 tgl@sss.pgh.pa.us 1603 :CBC 157 : topxid = SubTransGetTopmostTransaction(xid);
1604 [ - + ]: 157 : Assert(TransactionIdIsValid(topxid));
570 michael@paquier.xyz 1605 [ + - + - ]: 314 : if (!TransactionIdEquals(topxid, xid) &&
1606 : 157 : pg_lfind32(topxid, xids, nxids))
1607 : 157 : return true;
1608 : :
657 heikki.linnakangas@i 1609 :UBC 0 : cachedXidIsNotInProgress = xid;
6050 tgl@sss.pgh.pa.us 1610 : 0 : return false;
1611 : : }
1612 : :
1613 : : /*
1614 : : * TransactionIdIsActive -- is xid the top-level XID of an active backend?
1615 : : *
1616 : : * This differs from TransactionIdIsInProgress in that it ignores prepared
1617 : : * transactions, as well as transactions running on the primary if we're in
1618 : : * hot standby. Also, we ignore subtransactions since that's not needed
1619 : : * for current uses.
1620 : : */
1621 : : bool
6876 1622 : 0 : TransactionIdIsActive(TransactionId xid)
1623 : : {
1624 : 0 : bool result = false;
1625 : 0 : ProcArrayStruct *arrayP = procArray;
1339 andres@anarazel.de 1626 : 0 : TransactionId *other_xids = ProcGlobal->xids;
1627 : : int i;
1628 : :
1629 : : /*
1630 : : * Don't bother checking a transaction older than RecentXmin; it could not
1631 : : * possibly still be running.
1632 : : */
6876 tgl@sss.pgh.pa.us 1633 [ # # ]: 0 : if (TransactionIdPrecedes(xid, RecentXmin))
1634 : 0 : return false;
1635 : :
1636 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1637 : :
1638 [ # # ]: 0 : for (i = 0; i < arrayP->numProcs; i++)
1639 : : {
4326 bruce@momjian.us 1640 : 0 : int pgprocno = arrayP->pgprocnos[i];
1983 andres@anarazel.de 1641 : 0 : PGPROC *proc = &allProcs[pgprocno];
1642 : : TransactionId pxid;
1643 : :
1644 : : /* Fetch xid just once - see GetNewTransactionId */
1339 1645 : 0 : pxid = UINT32_ACCESS_ONCE(other_xids[i]);
1646 : :
6876 tgl@sss.pgh.pa.us 1647 [ # # ]: 0 : if (!TransactionIdIsValid(pxid))
1648 : 0 : continue;
1649 : :
1650 [ # # ]: 0 : if (proc->pid == 0)
1651 : 0 : continue; /* ignore prepared transactions */
1652 : :
1653 [ # # ]: 0 : if (TransactionIdEquals(pxid, xid))
1654 : : {
1655 : 0 : result = true;
1656 : 0 : break;
1657 : : }
1658 : : }
1659 : :
1660 : 0 : LWLockRelease(ProcArrayLock);
1661 : :
1662 : 0 : return result;
1663 : : }
1664 : :
1665 : :
1666 : : /*
1667 : : * Determine XID horizons.
1668 : : *
1669 : : * This is used by wrapper functions like GetOldestNonRemovableTransactionId()
1670 : : * (for VACUUM), GetReplicationHorizons() (for hot_standby_feedback), etc as
1671 : : * well as "internally" by GlobalVisUpdate() (see comment above struct
1672 : : * GlobalVisState).
1673 : : *
1674 : : * See the definition of ComputeXidHorizonsResult for the various computed
1675 : : * horizons.
1676 : : *
1677 : : * For VACUUM separate horizons (used to decide which deleted tuples must
1678 : : * be preserved), for shared and non-shared tables are computed. For shared
1679 : : * relations backends in all databases must be considered, but for non-shared
1680 : : * relations that's not required, since only backends in my own database could
1681 : : * ever see the tuples in them. Also, we can ignore concurrently running lazy
1682 : : * VACUUMs because (a) they must be working on other tables, and (b) they
1683 : : * don't need to do snapshot-based lookups.
1684 : : *
1685 : : * This also computes a horizon used to truncate pg_subtrans. For that
1686 : : * backends in all databases have to be considered, and concurrently running
1687 : : * lazy VACUUMs cannot be ignored, as they still may perform pg_subtrans
1688 : : * accesses.
1689 : : *
1690 : : * Note: we include all currently running xids in the set of considered xids.
1691 : : * This ensures that if a just-started xact has not yet set its snapshot,
1692 : : * when it does set the snapshot it cannot set xmin less than what we compute.
1693 : : * See notes in src/backend/access/transam/README.
1694 : : *
1695 : : * Note: despite the above, it's possible for the calculated values to move
1696 : : * backwards on repeated calls. The calculated values are conservative, so
1697 : : * that anything older is definitely not considered as running by anyone
1698 : : * anymore, but the exact values calculated depend on a number of things. For
1699 : : * example, if there are no transactions running in the current database, the
1700 : : * horizon for normal tables will be latestCompletedXid. If a transaction
1701 : : * begins after that, its xmin will include in-progress transactions in other
1702 : : * databases that started earlier, so another call will return a lower value.
1703 : : * Nonetheless it is safe to vacuum a table in the current database with the
1704 : : * first result. There are also replication-related effects: a walsender
1705 : : * process can set its xmin based on transactions that are no longer running
1706 : : * on the primary but are still being replayed on the standby, thus possibly
1707 : : * making the values go backwards. In this case there is a possibility that
1708 : : * we lose data that the standby would like to have, but unless the standby
1709 : : * uses a replication slot to make its xmin persistent there is little we can
1710 : : * do about that --- data is only protected if the walsender runs continuously
1711 : : * while queries are executed on the standby. (The Hot Standby code deals
1712 : : * with such cases by failing standby queries that needed to access
1713 : : * already-removed data, so there's no integrity bug.)
1714 : : *
1715 : : * Note: the approximate horizons (see definition of GlobalVisState) are
1716 : : * updated by the computations done here. That's currently required for
1717 : : * correctness and a small optimization. Without doing so it's possible that
1718 : : * heap vacuum's call to heap_page_prune_and_freeze() uses a more conservative
1719 : : * horizon than later when deciding which tuples can be removed - which the
1720 : : * code doesn't expect (breaking HOT).
1721 : : */
1722 : : static void
1341 andres@anarazel.de 1723 :CBC 157391 : ComputeXidHorizons(ComputeXidHorizonsResult *h)
1724 : : {
6905 tgl@sss.pgh.pa.us 1725 : 157391 : ProcArrayStruct *arrayP = procArray;
1726 : : TransactionId kaxmin;
1341 andres@anarazel.de 1727 : 157391 : bool in_recovery = RecoveryInProgress();
1339 1728 : 157391 : TransactionId *other_xids = ProcGlobal->xids;
1729 : :
1730 : : /* inferred after ProcArrayLock is released */
684 alvherre@alvh.no-ip. 1731 : 157391 : h->catalog_oldest_nonremovable = InvalidTransactionId;
1732 : :
6063 tgl@sss.pgh.pa.us 1733 : 157391 : LWLockAcquire(ProcArrayLock, LW_SHARED);
1734 : :
128 heikki.linnakangas@i 1735 :GNC 157391 : h->latest_completed = TransamVariables->latestCompletedXid;
1736 : :
1737 : : /*
1738 : : * We initialize the MIN() calculation with latestCompletedXid + 1. This
1739 : : * is a lower bound for the XIDs that might appear in the ProcArray later,
1740 : : * and so protects us against overestimating the result due to future
1741 : : * additions.
1742 : : */
1743 : : {
1744 : : TransactionId initial;
1745 : :
1341 andres@anarazel.de 1746 :CBC 157391 : initial = XidFromFullTransactionId(h->latest_completed);
1747 [ - + ]: 157391 : Assert(TransactionIdIsValid(initial));
1748 [ - + ]: 157391 : TransactionIdAdvance(initial);
1749 : :
1750 : 157391 : h->oldest_considered_running = initial;
1751 : 157391 : h->shared_oldest_nonremovable = initial;
1752 : 157391 : h->data_oldest_nonremovable = initial;
1753 : :
1754 : : /*
1755 : : * Only modifications made by this backend affect the horizon for
1756 : : * temporary relations. Instead of a check in each iteration of the
1757 : : * loop over all PGPROCs it is cheaper to just initialize to the
1758 : : * current top-level xid any.
1759 : : *
1760 : : * Without an assigned xid we could use a horizon as aggressive as
1761 : : * GetNewTransactionId(), but we can get away with the much cheaper
1762 : : * latestCompletedXid + 1: If this backend has no xid there, by
1763 : : * definition, can't be any newer changes in the temp table than
1764 : : * latestCompletedXid.
1765 : : */
1264 1766 [ + + ]: 157391 : if (TransactionIdIsValid(MyProc->xid))
1767 : 29237 : h->temp_oldest_nonremovable = MyProc->xid;
1768 : : else
1769 : 128154 : h->temp_oldest_nonremovable = initial;
1770 : : }
1771 : :
1772 : : /*
1773 : : * Fetch slot horizons while ProcArrayLock is held - the
1774 : : * LWLockAcquire/LWLockRelease are a barrier, ensuring this happens inside
1775 : : * the lock.
1776 : : */
1341 1777 : 157391 : h->slot_xmin = procArray->replication_slot_xmin;
1778 : 157391 : h->slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
1779 : :
1780 [ + + ]: 887599 : for (int index = 0; index < arrayP->numProcs; index++)
1781 : : {
4326 bruce@momjian.us 1782 : 730208 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 1783 : 730208 : PGPROC *proc = &allProcs[pgprocno];
1245 alvherre@alvh.no-ip. 1784 : 730208 : int8 statusFlags = ProcGlobal->statusFlags[index];
1785 : : TransactionId xid;
1786 : : TransactionId xmin;
1787 : :
1788 : : /* Fetch xid just once - see GetNewTransactionId */
1337 andres@anarazel.de 1789 : 730208 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
1340 1790 : 730208 : xmin = UINT32_ACCESS_ONCE(proc->xmin);
1791 : :
1792 : : /*
1793 : : * Consider both the transaction's Xmin, and its Xid.
1794 : : *
1795 : : * We must check both because a transaction might have an Xmin but not
1796 : : * (yet) an Xid; conversely, if it has an Xid, that could determine
1797 : : * some not-yet-set Xmin.
1798 : : */
1341 1799 : 730208 : xmin = TransactionIdOlder(xmin, xid);
1800 : :
1801 : : /* if neither is set, this proc doesn't influence the horizon */
1302 peter@eisentraut.org 1802 [ + + ]: 730208 : if (!TransactionIdIsValid(xmin))
6468 alvherre@alvh.no-ip. 1803 : 293258 : continue;
1804 : :
1805 : : /*
1806 : : * Don't ignore any procs when determining which transactions might be
1807 : : * considered running. While slots should ensure logical decoding
1808 : : * backends are protected even without this check, it can't hurt to
1809 : : * include them here as well..
1810 : : */
1341 andres@anarazel.de 1811 : 436950 : h->oldest_considered_running =
1812 : 436950 : TransactionIdOlder(h->oldest_considered_running, xmin);
1813 : :
1814 : : /*
1815 : : * Skip over backends either vacuuming (which is ok with rows being
1816 : : * removed, as long as pg_subtrans is not truncated) or doing logical
1817 : : * decoding (which manages xmin separately, check below).
1818 : : */
1245 alvherre@alvh.no-ip. 1819 [ + + ]: 436950 : if (statusFlags & (PROC_IN_VACUUM | PROC_IN_LOGICAL_DECODING))
1341 andres@anarazel.de 1820 : 122104 : continue;
1821 : :
1822 : : /* shared tables need to take backends in all databases into account */
1823 : 314846 : h->shared_oldest_nonremovable =
1824 : 314846 : TransactionIdOlder(h->shared_oldest_nonremovable, xmin);
1825 : :
1826 : : /*
1827 : : * Normally sessions in other databases are ignored for anything but
1828 : : * the shared horizon.
1829 : : *
1830 : : * However, include them when MyDatabaseId is not (yet) set. A
1831 : : * backend in the process of starting up must not compute a "too
1832 : : * aggressive" horizon, otherwise we could end up using it to prune
1833 : : * still-needed data away. If the current backend never connects to a
1834 : : * database this is harmless, because data_oldest_nonremovable will
1835 : : * never be utilized.
1836 : : *
1837 : : * Also, sessions marked with PROC_AFFECTS_ALL_HORIZONS should always
1838 : : * be included. (This flag is used for hot standby feedback, which
1839 : : * can't be tied to a specific database.)
1840 : : *
1841 : : * Also, while in recovery we cannot compute an accurate per-database
1842 : : * horizon, as all xids are managed via the KnownAssignedXids
1843 : : * machinery.
1844 : : */
730 tgl@sss.pgh.pa.us 1845 [ + + ]: 314846 : if (proc->databaseId == MyDatabaseId ||
1846 [ + + ]: 18624 : MyDatabaseId == InvalidOid ||
1847 [ + - - + ]: 13391 : (statusFlags & PROC_AFFECTS_ALL_HORIZONS) ||
1848 : : in_recovery)
1849 : : {
684 alvherre@alvh.no-ip. 1850 : 301455 : h->data_oldest_nonremovable =
1851 : 301455 : TransactionIdOlder(h->data_oldest_nonremovable, xmin);
1852 : : }
1853 : : }
1854 : :
1855 : : /*
1856 : : * If in recovery fetch oldest xid in KnownAssignedXids, will be applied
1857 : : * after lock is released.
1858 : : */
1341 andres@anarazel.de 1859 [ + + ]: 157391 : if (in_recovery)
1860 : 192 : kaxmin = KnownAssignedXidsGetOldestXmin();
1861 : :
1862 : : /*
1863 : : * No other information from shared state is needed, release the lock
1864 : : * immediately. The rest of the computations can be done without a lock.
1865 : : */
1866 : 157391 : LWLockRelease(ProcArrayLock);
1867 : :
1868 [ + + ]: 157391 : if (in_recovery)
1869 : : {
1870 : 192 : h->oldest_considered_running =
1871 : 192 : TransactionIdOlder(h->oldest_considered_running, kaxmin);
1872 : 192 : h->shared_oldest_nonremovable =
1873 : 192 : TransactionIdOlder(h->shared_oldest_nonremovable, kaxmin);
1874 : 192 : h->data_oldest_nonremovable =
1875 : 192 : TransactionIdOlder(h->data_oldest_nonremovable, kaxmin);
1876 : : /* temp relations cannot be accessed in recovery */
1877 : : }
1878 : :
356 1879 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1880 : : h->shared_oldest_nonremovable));
1881 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1882 : : h->data_oldest_nonremovable));
1883 : :
1884 : : /*
1885 : : * Check whether there are replication slots requiring an older xmin.
1886 : : */
1341 1887 : 157391 : h->shared_oldest_nonremovable =
1888 : 157391 : TransactionIdOlder(h->shared_oldest_nonremovable, h->slot_xmin);
1889 : 157391 : h->data_oldest_nonremovable =
1890 : 157391 : TransactionIdOlder(h->data_oldest_nonremovable, h->slot_xmin);
1891 : :
1892 : : /*
1893 : : * The only difference between catalog / data horizons is that the slot's
1894 : : * catalog xmin is applied to the catalog one (so catalogs can be accessed
1895 : : * for logical decoding). Initialize with data horizon, and then back up
1896 : : * further if necessary. Have to back up the shared horizon as well, since
1897 : : * that also can contain catalogs.
1898 : : */
1899 : 157391 : h->shared_oldest_nonremovable_raw = h->shared_oldest_nonremovable;
1900 : 157391 : h->shared_oldest_nonremovable =
1901 : 157391 : TransactionIdOlder(h->shared_oldest_nonremovable,
1902 : : h->slot_catalog_xmin);
684 alvherre@alvh.no-ip. 1903 : 157391 : h->catalog_oldest_nonremovable = h->data_oldest_nonremovable;
1341 andres@anarazel.de 1904 : 157391 : h->catalog_oldest_nonremovable =
1905 : 157391 : TransactionIdOlder(h->catalog_oldest_nonremovable,
1906 : : h->slot_catalog_xmin);
1907 : :
1908 : : /*
1909 : : * It's possible that slots backed up the horizons further than
1910 : : * oldest_considered_running. Fix.
1911 : : */
1912 : 157391 : h->oldest_considered_running =
1913 : 157391 : TransactionIdOlder(h->oldest_considered_running,
1914 : : h->shared_oldest_nonremovable);
1915 : 157391 : h->oldest_considered_running =
1916 : 157391 : TransactionIdOlder(h->oldest_considered_running,
1917 : : h->catalog_oldest_nonremovable);
1918 : 157391 : h->oldest_considered_running =
1919 : 157391 : TransactionIdOlder(h->oldest_considered_running,
1920 : : h->data_oldest_nonremovable);
1921 : :
1922 : : /*
1923 : : * shared horizons have to be at least as old as the oldest visible in
1924 : : * current db
1925 : : */
1926 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1927 : : h->data_oldest_nonremovable));
1928 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->shared_oldest_nonremovable,
1929 : : h->catalog_oldest_nonremovable));
1930 : :
1931 : : /*
1932 : : * Horizons need to ensure that pg_subtrans access is still possible for
1933 : : * the relevant backends.
1934 : : */
1935 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1936 : : h->shared_oldest_nonremovable));
1937 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1938 : : h->catalog_oldest_nonremovable));
1939 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1940 : : h->data_oldest_nonremovable));
1264 1941 [ - + ]: 157391 : Assert(TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1942 : : h->temp_oldest_nonremovable));
1341 1943 [ + + - + ]: 157391 : Assert(!TransactionIdIsValid(h->slot_xmin) ||
1944 : : TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1945 : : h->slot_xmin));
1946 [ + + - + ]: 157391 : Assert(!TransactionIdIsValid(h->slot_catalog_xmin) ||
1947 : : TransactionIdPrecedesOrEquals(h->oldest_considered_running,
1948 : : h->slot_catalog_xmin));
1949 : :
1950 : : /* update approximate horizons with the computed horizons */
1951 : 157391 : GlobalVisUpdateApply(h);
1952 : 157391 : }
1953 : :
1954 : : /*
1955 : : * Determine what kind of visibility horizon needs to be used for a
1956 : : * relation. If rel is NULL, the most conservative horizon is used.
1957 : : */
1958 : : static inline GlobalVisHorizonKind
995 1959 : 13751892 : GlobalVisHorizonKindForRel(Relation rel)
1960 : : {
1961 : : /*
1962 : : * Other relkinds currently don't contain xids, nor always the necessary
1963 : : * logical decoding markers.
1964 : : */
1965 [ + + + + : 13751892 : Assert(!rel ||
+ + - + ]
1966 : : rel->rd_rel->relkind == RELKIND_RELATION ||
1967 : : rel->rd_rel->relkind == RELKIND_MATVIEW ||
1968 : : rel->rd_rel->relkind == RELKIND_TOASTVALUE);
1969 : :
1970 [ + + + + : 13751892 : if (rel == NULL || rel->rd_rel->relisshared || RecoveryInProgress())
+ + ]
1971 : 81183 : return VISHORIZON_SHARED;
1972 [ + + ]: 13670709 : else if (IsCatalogRelation(rel) ||
1973 [ + + + + : 11365949 : RelationIsAccessibleInLogicalDecoding(rel))
- + - - -
- + - + +
- + - - +
- ]
1974 : 2304764 : return VISHORIZON_CATALOG;
1975 [ + + + + ]: 11365945 : else if (!RELATION_IS_LOCAL(rel))
1976 : 11312761 : return VISHORIZON_DATA;
1977 : : else
1978 : 53184 : return VISHORIZON_TEMP;
1979 : : }
1980 : :
1981 : : /*
1982 : : * Return the oldest XID for which deleted tuples must be preserved in the
1983 : : * passed table.
1984 : : *
1985 : : * If rel is not NULL the horizon may be considerably more recent than
1986 : : * otherwise (i.e. fewer tuples will be removable). In the NULL case a horizon
1987 : : * that is correct (but not optimal) for all relations will be returned.
1988 : : *
1989 : : * This is used by VACUUM to decide which deleted tuples must be preserved in
1990 : : * the passed in table.
1991 : : */
1992 : : TransactionId
1341 1993 : 111289 : GetOldestNonRemovableTransactionId(Relation rel)
1994 : : {
1995 : : ComputeXidHorizonsResult horizons;
1996 : :
1997 : 111289 : ComputeXidHorizons(&horizons);
1998 : :
995 1999 [ + + + + : 111289 : switch (GlobalVisHorizonKindForRel(rel))
- ]
2000 : : {
2001 : 17544 : case VISHORIZON_SHARED:
2002 : 17544 : return horizons.shared_oldest_nonremovable;
2003 : 64549 : case VISHORIZON_CATALOG:
2004 : 64549 : return horizons.catalog_oldest_nonremovable;
2005 : 17830 : case VISHORIZON_DATA:
2006 : 17830 : return horizons.data_oldest_nonremovable;
2007 : 11366 : case VISHORIZON_TEMP:
2008 : 11366 : return horizons.temp_oldest_nonremovable;
2009 : : }
2010 : :
2011 : : /* just to prevent compiler warnings */
995 andres@anarazel.de 2012 :UBC 0 : return InvalidTransactionId;
2013 : : }
2014 : :
2015 : : /*
2016 : : * Return the oldest transaction id any currently running backend might still
2017 : : * consider running. This should not be used for visibility / pruning
2018 : : * determinations (see GetOldestNonRemovableTransactionId()), but for
2019 : : * decisions like up to where pg_subtrans can be truncated.
2020 : : */
2021 : : TransactionId
1341 andres@anarazel.de 2022 :CBC 1039 : GetOldestTransactionIdConsideredRunning(void)
2023 : : {
2024 : : ComputeXidHorizonsResult horizons;
2025 : :
2026 : 1039 : ComputeXidHorizons(&horizons);
2027 : :
2028 : 1039 : return horizons.oldest_considered_running;
2029 : : }
2030 : :
2031 : : /*
2032 : : * Return the visibility horizons for a hot standby feedback message.
2033 : : */
2034 : : void
2035 : 34 : GetReplicationHorizons(TransactionId *xmin, TransactionId *catalog_xmin)
2036 : : {
2037 : : ComputeXidHorizonsResult horizons;
2038 : :
2039 : 34 : ComputeXidHorizons(&horizons);
2040 : :
2041 : : /*
2042 : : * Don't want to use shared_oldest_nonremovable here, as that contains the
2043 : : * effect of replication slot's catalog_xmin. We want to send a separate
2044 : : * feedback for the catalog horizon, so the primary can remove data table
2045 : : * contents more aggressively.
2046 : : */
2047 : 34 : *xmin = horizons.shared_oldest_nonremovable_raw;
2048 : 34 : *catalog_xmin = horizons.slot_catalog_xmin;
6905 tgl@sss.pgh.pa.us 2049 : 34 : }
2050 : :
2051 : : /*
2052 : : * GetMaxSnapshotXidCount -- get max size for snapshot XID array
2053 : : *
2054 : : * We have to export this for use by snapmgr.c.
2055 : : */
2056 : : int
4558 2057 : 33704 : GetMaxSnapshotXidCount(void)
2058 : : {
2059 : 33704 : return procArray->maxProcs;
2060 : : }
2061 : :
2062 : : /*
2063 : : * GetMaxSnapshotSubxidCount -- get max size for snapshot sub-XID array
2064 : : *
2065 : : * We have to export this for use by snapmgr.c.
2066 : : */
2067 : : int
2068 : 33544 : GetMaxSnapshotSubxidCount(void)
2069 : : {
2070 : 33544 : return TOTAL_MAX_CACHED_SUBXIDS;
2071 : : }
2072 : :
2073 : : /*
2074 : : * Helper function for GetSnapshotData() that checks if the bulk of the
2075 : : * visibility information in the snapshot is still valid. If so, it updates
2076 : : * the fields that need to change and returns true. Otherwise it returns
2077 : : * false.
2078 : : *
2079 : : * This very likely can be evolved to not need ProcArrayLock held (at very
2080 : : * least in the case we already hold a snapshot), but that's for another day.
2081 : : */
2082 : : static bool
1336 andres@anarazel.de 2083 : 1874856 : GetSnapshotDataReuse(Snapshot snapshot)
2084 : : {
2085 : : uint64 curXactCompletionCount;
2086 : :
2087 [ - + ]: 1874856 : Assert(LWLockHeldByMe(ProcArrayLock));
2088 : :
2089 [ + + ]: 1874856 : if (unlikely(snapshot->snapXactCompletionCount == 0))
2090 : 32208 : return false;
2091 : :
128 heikki.linnakangas@i 2092 :GNC 1842648 : curXactCompletionCount = TransamVariables->xactCompletionCount;
1336 andres@anarazel.de 2093 [ + + ]:CBC 1842648 : if (curXactCompletionCount != snapshot->snapXactCompletionCount)
2094 : 353991 : return false;
2095 : :
2096 : : /*
2097 : : * If the current xactCompletionCount is still the same as it was at the
2098 : : * time the snapshot was built, we can be sure that rebuilding the
2099 : : * contents of the snapshot the hard way would result in the same snapshot
2100 : : * contents:
2101 : : *
2102 : : * As explained in transam/README, the set of xids considered running by
2103 : : * GetSnapshotData() cannot change while ProcArrayLock is held. Snapshot
2104 : : * contents only depend on transactions with xids and xactCompletionCount
2105 : : * is incremented whenever a transaction with an xid finishes (while
2106 : : * holding ProcArrayLock exclusively). Thus the xactCompletionCount check
2107 : : * ensures we would detect if the snapshot would have changed.
2108 : : *
2109 : : * As the snapshot contents are the same as it was before, it is safe to
2110 : : * re-enter the snapshot's xmin into the PGPROC array. None of the rows
2111 : : * visible under the snapshot could already have been removed (that'd
2112 : : * require the set of running transactions to change) and it fulfills the
2113 : : * requirement that concurrent GetSnapshotData() calls yield the same
2114 : : * xmin.
2115 : : */
2116 [ + + ]: 1488657 : if (!TransactionIdIsValid(MyProc->xmin))
2117 : 593913 : MyProc->xmin = TransactionXmin = snapshot->xmin;
2118 : :
2119 : 1488657 : RecentXmin = snapshot->xmin;
2120 [ - + ]: 1488657 : Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
2121 : :
2122 : 1488657 : snapshot->curcid = GetCurrentCommandId(false);
2123 : 1488657 : snapshot->active_count = 0;
2124 : 1488657 : snapshot->regd_count = 0;
2125 : 1488657 : snapshot->copied = false;
222 tmunro@postgresql.or 2126 :GNC 1488657 : snapshot->lsn = InvalidXLogRecPtr;
2127 : 1488657 : snapshot->whenTaken = 0;
2128 : :
1336 andres@anarazel.de 2129 :CBC 1488657 : return true;
2130 : : }
2131 : :
2132 : : /*
2133 : : * GetSnapshotData -- returns information about running transactions.
2134 : : *
2135 : : * The returned snapshot includes xmin (lowest still-running xact ID),
2136 : : * xmax (highest completed xact ID + 1), and a list of running xact IDs
2137 : : * in the range xmin <= xid < xmax. It is used as follows:
2138 : : * All xact IDs < xmin are considered finished.
2139 : : * All xact IDs >= xmax are considered still running.
2140 : : * For an xact ID xmin <= xid < xmax, consult list to see whether
2141 : : * it is considered running or not.
2142 : : * This ensures that the set of transactions seen as "running" by the
2143 : : * current xact will not change after it takes the snapshot.
2144 : : *
2145 : : * All running top-level XIDs are included in the snapshot, except for lazy
2146 : : * VACUUM processes. We also try to include running subtransaction XIDs,
2147 : : * but since PGPROC has only a limited cache area for subxact XIDs, full
2148 : : * information may not be available. If we find any overflowed subxid arrays,
2149 : : * we have to mark the snapshot's subxid data as overflowed, and extra work
2150 : : * *may* need to be done to determine what's running (see XidInMVCCSnapshot()).
2151 : : *
2152 : : * We also update the following backend-global variables:
2153 : : * TransactionXmin: the oldest xmin of any snapshot in use in the
2154 : : * current transaction (this is the same as MyProc->xmin).
2155 : : * RecentXmin: the xmin computed for the most recent snapshot. XIDs
2156 : : * older than this are known not running any more.
2157 : : *
2158 : : * And try to advance the bounds of GlobalVis{Shared,Catalog,Data,Temp}Rels
2159 : : * for the benefit of the GlobalVisTest* family of functions.
2160 : : *
2161 : : * Note: this function should probably not be called with an argument that's
2162 : : * not statically allocated (see xip allocation below).
2163 : : */
2164 : : Snapshot
5816 alvherre@alvh.no-ip. 2165 : 1874856 : GetSnapshotData(Snapshot snapshot)
2166 : : {
6905 tgl@sss.pgh.pa.us 2167 : 1874856 : ProcArrayStruct *arrayP = procArray;
1339 andres@anarazel.de 2168 : 1874856 : TransactionId *other_xids = ProcGlobal->xids;
2169 : : TransactionId xmin;
2170 : : TransactionId xmax;
941 fujii@postgresql.org 2171 : 1874856 : int count = 0;
6433 tgl@sss.pgh.pa.us 2172 : 1874856 : int subcount = 0;
5230 simon@2ndQuadrant.co 2173 : 1874856 : bool suboverflowed = false;
2174 : : FullTransactionId latest_completed;
2175 : : TransactionId oldestxid;
2176 : : int mypgxactoff;
2177 : : TransactionId myxid;
2178 : : uint64 curXactCompletionCount;
2179 : :
1983 andres@anarazel.de 2180 : 1874856 : TransactionId replication_slot_xmin = InvalidTransactionId;
2181 : 1874856 : TransactionId replication_slot_catalog_xmin = InvalidTransactionId;
2182 : :
6905 tgl@sss.pgh.pa.us 2183 [ - + ]: 1874856 : Assert(snapshot != NULL);
2184 : :
2185 : : /*
2186 : : * Allocating space for maxProcs xids is usually overkill; numProcs would
2187 : : * be sufficient. But it seems better to do the malloc while not holding
2188 : : * the lock, so we can't look at numProcs. Likewise, we allocate much
2189 : : * more subxip storage than is probably needed.
2190 : : *
2191 : : * This does open a possibility for avoiding repeated malloc/free: since
2192 : : * maxProcs does not change at runtime, we can simply reuse the previous
2193 : : * xip arrays if any. (This relies on the fact that all callers pass
2194 : : * static SnapshotData structs.)
2195 : : */
2196 [ + + ]: 1874856 : if (snapshot->xip == NULL)
2197 : : {
2198 : : /*
2199 : : * First call for this snapshot. Snapshot is same size whether or not
2200 : : * we are in recovery, see later comments.
2201 : : */
2202 : 32008 : snapshot->xip = (TransactionId *)
4558 2203 : 32008 : malloc(GetMaxSnapshotXidCount() * sizeof(TransactionId));
6905 2204 [ - + ]: 32008 : if (snapshot->xip == NULL)
6905 tgl@sss.pgh.pa.us 2205 [ # # ]:UBC 0 : ereport(ERROR,
2206 : : (errcode(ERRCODE_OUT_OF_MEMORY),
2207 : : errmsg("out of memory")));
6433 tgl@sss.pgh.pa.us 2208 [ - + ]:CBC 32008 : Assert(snapshot->subxip == NULL);
2209 : 32008 : snapshot->subxip = (TransactionId *)
4558 2210 : 32008 : malloc(GetMaxSnapshotSubxidCount() * sizeof(TransactionId));
6433 2211 [ - + ]: 32008 : if (snapshot->subxip == NULL)
6433 tgl@sss.pgh.pa.us 2212 [ # # ]:UBC 0 : ereport(ERROR,
2213 : : (errcode(ERRCODE_OUT_OF_MEMORY),
2214 : : errmsg("out of memory")));
2215 : : }
2216 : :
2217 : : /*
2218 : : * It is sufficient to get shared lock on ProcArrayLock, even if we are
2219 : : * going to set MyProc->xmin.
2220 : : */
6433 tgl@sss.pgh.pa.us 2221 :CBC 1874856 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2222 : :
1336 andres@anarazel.de 2223 [ + + ]: 1874856 : if (GetSnapshotDataReuse(snapshot))
2224 : : {
2225 : 1488657 : LWLockRelease(ProcArrayLock);
2226 : 1488657 : return snapshot;
2227 : : }
2228 : :
128 heikki.linnakangas@i 2229 :GNC 386199 : latest_completed = TransamVariables->latestCompletedXid;
1339 andres@anarazel.de 2230 :CBC 386199 : mypgxactoff = MyProc->pgxactoff;
2231 : 386199 : myxid = other_xids[mypgxactoff];
2232 [ - + ]: 386199 : Assert(myxid == MyProc->xid);
2233 : :
128 heikki.linnakangas@i 2234 :GNC 386199 : oldestxid = TransamVariables->oldestXid;
2235 : 386199 : curXactCompletionCount = TransamVariables->xactCompletionCount;
2236 : :
2237 : : /* xmax is always latestCompletedXid + 1 */
1342 andres@anarazel.de 2238 :CBC 386199 : xmax = XidFromFullTransactionId(latest_completed);
6063 tgl@sss.pgh.pa.us 2239 [ - + ]: 386199 : TransactionIdAdvance(xmax);
1342 andres@anarazel.de 2240 [ - + ]: 386199 : Assert(TransactionIdIsNormal(xmax));
2241 : :
2242 : : /* initialize xmin calculation with xmax */
1341 2243 : 386199 : xmin = xmax;
2244 : :
2245 : : /* take own xid into account, saves a check inside the loop */
1339 2246 [ + + + - : 386199 : if (TransactionIdIsNormal(myxid) && NormalTransactionIdPrecedes(myxid, xmin))
- + + + ]
2247 : 38432 : xmin = myxid;
2248 : :
5109 simon@2ndQuadrant.co 2249 : 386199 : snapshot->takenDuringRecovery = RecoveryInProgress();
2250 : :
5110 2251 [ + + ]: 386199 : if (!snapshot->takenDuringRecovery)
2252 : : {
941 fujii@postgresql.org 2253 : 385176 : int numProcs = arrayP->numProcs;
1339 andres@anarazel.de 2254 : 385176 : TransactionId *xip = snapshot->xip;
4326 bruce@momjian.us 2255 : 385176 : int *pgprocnos = arrayP->pgprocnos;
1339 andres@anarazel.de 2256 : 385176 : XidCacheStatus *subxidStates = ProcGlobal->subxidStates;
1245 alvherre@alvh.no-ip. 2257 : 385176 : uint8 *allStatusFlags = ProcGlobal->statusFlags;
2258 : :
2259 : : /*
2260 : : * First collect set of pgxactoff/xids that need to be included in the
2261 : : * snapshot.
2262 : : */
941 fujii@postgresql.org 2263 [ + + ]: 3653586 : for (int pgxactoff = 0; pgxactoff < numProcs; pgxactoff++)
2264 : : {
2265 : : /* Fetch xid just once - see GetNewTransactionId */
1339 andres@anarazel.de 2266 : 3268410 : TransactionId xid = UINT32_ACCESS_ONCE(other_xids[pgxactoff]);
2267 : : uint8 statusFlags;
2268 : :
2269 [ - + ]: 3268410 : Assert(allProcs[arrayP->pgprocnos[pgxactoff]].pgxactoff == pgxactoff);
2270 : :
2271 : : /*
2272 : : * If the transaction has no XID assigned, we can skip it; it
2273 : : * won't have sub-XIDs either.
2274 : : */
2275 [ + + ]: 3268410 : if (likely(xid == InvalidTransactionId))
6066 tgl@sss.pgh.pa.us 2276 : 2485001 : continue;
2277 : :
2278 : : /*
2279 : : * We don't include our own XIDs (if any) in the snapshot. It
2280 : : * needs to be included in the xmin computation, but we did so
2281 : : * outside the loop.
2282 : : */
1339 andres@anarazel.de 2283 [ + + ]: 783409 : if (pgxactoff == mypgxactoff)
2284 : 63917 : continue;
2285 : :
2286 : : /*
2287 : : * The only way we are able to get here with a non-normal xid is
2288 : : * during bootstrap - with this backend using
2289 : : * BootstrapTransactionId. But the above test should filter that
2290 : : * out.
2291 : : */
2292 [ - + ]: 719492 : Assert(TransactionIdIsNormal(xid));
2293 : :
2294 : : /*
2295 : : * If the XID is >= xmax, we can skip it; such transactions will
2296 : : * be treated as running anyway (and any sub-XIDs will also be >=
2297 : : * xmax).
2298 : : */
2299 [ + - - + : 719492 : if (!NormalTransactionIdPrecedes(xid, xmax))
+ + ]
4326 bruce@momjian.us 2300 : 152514 : continue;
2301 : :
2302 : : /*
2303 : : * Skip over backends doing logical decoding which manages xmin
2304 : : * separately (check below) and ones running LAZY VACUUM.
2305 : : */
1245 alvherre@alvh.no-ip. 2306 : 566978 : statusFlags = allStatusFlags[pgxactoff];
2307 [ + + ]: 566978 : if (statusFlags & (PROC_IN_LOGICAL_DECODING | PROC_IN_VACUUM))
1339 andres@anarazel.de 2308 : 93 : continue;
2309 : :
4503 rhaas@postgresql.org 2310 [ + - - + : 566885 : if (NormalTransactionIdPrecedes(xid, xmin))
+ + ]
2311 : 310781 : xmin = xid;
2312 : :
2313 : : /* Add XID to snapshot. */
1339 andres@anarazel.de 2314 : 566885 : xip[count++] = xid;
2315 : :
2316 : : /*
2317 : : * Save subtransaction XIDs if possible (if we've already
2318 : : * overflowed, there's no point). Note that the subxact XIDs must
2319 : : * be later than their parent, so no need to check them against
2320 : : * xmin. We could filter against xmax, but it seems better not to
2321 : : * do that much work while holding the ProcArrayLock.
2322 : : *
2323 : : * The other backend can add more subxids concurrently, but cannot
2324 : : * remove any. Hence it's important to fetch nxids just once.
2325 : : * Should be safe to use memcpy, though. (We needn't worry about
2326 : : * missing any xids added concurrently, because they must postdate
2327 : : * xmax.)
2328 : : *
2329 : : * Again, our own XIDs are not included in the snapshot.
2330 : : */
4503 rhaas@postgresql.org 2331 [ + + ]: 566885 : if (!suboverflowed)
2332 : : {
2333 : :
1339 andres@anarazel.de 2334 [ + + ]: 566881 : if (subxidStates[pgxactoff].overflowed)
5110 simon@2ndQuadrant.co 2335 : 34 : suboverflowed = true;
2336 : : else
2337 : : {
1339 andres@anarazel.de 2338 : 566847 : int nsubxids = subxidStates[pgxactoff].count;
2339 : :
2340 [ + + ]: 566847 : if (nsubxids > 0)
2341 : : {
2342 : 5176 : int pgprocno = pgprocnos[pgxactoff];
1983 2343 : 5176 : PGPROC *proc = &allProcs[pgprocno];
2344 : :
2345 : 5176 : pg_read_barrier(); /* pairs with GetNewTransactionId */
2346 : :
5110 simon@2ndQuadrant.co 2347 : 5176 : memcpy(snapshot->subxip + subcount,
432 peter@eisentraut.org 2348 : 5176 : proc->subxids.xids,
2349 : : nsubxids * sizeof(TransactionId));
1339 andres@anarazel.de 2350 : 5176 : subcount += nsubxids;
2351 : : }
2352 : : }
2353 : : }
2354 : : }
2355 : : }
2356 : : else
2357 : : {
2358 : : /*
2359 : : * We're in hot standby, so get XIDs from KnownAssignedXids.
2360 : : *
2361 : : * We store all xids directly into subxip[]. Here's why:
2362 : : *
2363 : : * In recovery we don't know which xids are top-level and which are
2364 : : * subxacts, a design choice that greatly simplifies xid processing.
2365 : : *
2366 : : * It seems like we would want to try to put xids into xip[] only, but
2367 : : * that is fairly small. We would either need to make that bigger or
2368 : : * to increase the rate at which we WAL-log xid assignment; neither is
2369 : : * an appealing choice.
2370 : : *
2371 : : * We could try to store xids into xip[] first and then into subxip[]
2372 : : * if there are too many xids. That only works if the snapshot doesn't
2373 : : * overflow because we do not search subxip[] in that case. A simpler
2374 : : * way is to just store all xids in the subxip array because this is
2375 : : * by far the bigger array. We just leave the xip array empty.
2376 : : *
2377 : : * Either way we need to change the way XidInMVCCSnapshot() works
2378 : : * depending upon when the snapshot was taken, or change normal
2379 : : * snapshot processing so it matches.
2380 : : *
2381 : : * Note: It is possible for recovery to end before we finish taking
2382 : : * the snapshot, and for newly assigned transaction ids to be added to
2383 : : * the ProcArray. xmax cannot change while we hold ProcArrayLock, so
2384 : : * those newly added transaction ids would be filtered away, so we
2385 : : * need not be concerned about them.
2386 : : */
5100 tgl@sss.pgh.pa.us 2387 : 1023 : subcount = KnownAssignedXidsGetAndSetXmin(snapshot->subxip, &xmin,
2388 : : xmax);
2389 : :
2390 [ + + ]: 1023 : if (TransactionIdPrecedesOrEquals(xmin, procArray->lastOverflowedXid))
5230 simon@2ndQuadrant.co 2391 : 4 : suboverflowed = true;
2392 : : }
2393 : :
2394 : :
2395 : : /*
2396 : : * Fetch into local variable while ProcArrayLock is held - the
2397 : : * LWLockRelease below is a barrier, ensuring this happens inside the
2398 : : * lock.
2399 : : */
3726 rhaas@postgresql.org 2400 : 386199 : replication_slot_xmin = procArray->replication_slot_xmin;
3695 2401 : 386199 : replication_slot_catalog_xmin = procArray->replication_slot_catalog_xmin;
2402 : :
1340 andres@anarazel.de 2403 [ + + ]: 386199 : if (!TransactionIdIsValid(MyProc->xmin))
2404 : 186030 : MyProc->xmin = TransactionXmin = xmin;
2405 : :
6905 tgl@sss.pgh.pa.us 2406 : 386199 : LWLockRelease(ProcArrayLock);
2407 : :
2408 : : /* maintain state for GlobalVis* */
2409 : : {
2410 : : TransactionId def_vis_xid;
2411 : : TransactionId def_vis_xid_data;
2412 : : FullTransactionId def_vis_fxid;
2413 : : FullTransactionId def_vis_fxid_data;
2414 : : FullTransactionId oldestfxid;
2415 : :
2416 : : /*
2417 : : * Converting oldestXid is only safe when xid horizon cannot advance,
2418 : : * i.e. holding locks. While we don't hold the lock anymore, all the
2419 : : * necessary data has been gathered with lock held.
2420 : : */
1341 andres@anarazel.de 2421 : 386199 : oldestfxid = FullXidRelativeTo(latest_completed, oldestxid);
2422 : :
2423 : : /* Check whether there's a replication slot requiring an older xmin. */
2424 : : def_vis_xid_data =
356 2425 : 386199 : TransactionIdOlder(xmin, replication_slot_xmin);
2426 : :
2427 : : /*
2428 : : * Rows in non-shared, non-catalog tables possibly could be vacuumed
2429 : : * if older than this xid.
2430 : : */
1341 2431 : 386199 : def_vis_xid = def_vis_xid_data;
2432 : :
2433 : : /*
2434 : : * Check whether there's a replication slot requiring an older catalog
2435 : : * xmin.
2436 : : */
2437 : : def_vis_xid =
2438 : 386199 : TransactionIdOlder(replication_slot_catalog_xmin, def_vis_xid);
2439 : :
2440 : 386199 : def_vis_fxid = FullXidRelativeTo(latest_completed, def_vis_xid);
2441 : 386199 : def_vis_fxid_data = FullXidRelativeTo(latest_completed, def_vis_xid_data);
2442 : :
2443 : : /*
2444 : : * Check if we can increase upper bound. As a previous
2445 : : * GlobalVisUpdate() might have computed more aggressive values, don't
2446 : : * overwrite them if so.
2447 : : */
2448 : : GlobalVisSharedRels.definitely_needed =
2449 : 386199 : FullTransactionIdNewer(def_vis_fxid,
2450 : : GlobalVisSharedRels.definitely_needed);
2451 : : GlobalVisCatalogRels.definitely_needed =
2452 : 386199 : FullTransactionIdNewer(def_vis_fxid,
2453 : : GlobalVisCatalogRels.definitely_needed);
2454 : : GlobalVisDataRels.definitely_needed =
2455 : 386199 : FullTransactionIdNewer(def_vis_fxid_data,
2456 : : GlobalVisDataRels.definitely_needed);
2457 : : /* See temp_oldest_nonremovable computation in ComputeXidHorizons() */
1264 2458 [ + + ]: 386199 : if (TransactionIdIsNormal(myxid))
2459 : : GlobalVisTempRels.definitely_needed =
2460 : 63839 : FullXidRelativeTo(latest_completed, myxid);
2461 : : else
2462 : : {
2463 : 322360 : GlobalVisTempRels.definitely_needed = latest_completed;
2464 : 322360 : FullTransactionIdAdvance(&GlobalVisTempRels.definitely_needed);
2465 : : }
2466 : :
2467 : : /*
2468 : : * Check if we know that we can initialize or increase the lower
2469 : : * bound. Currently the only cheap way to do so is to use
2470 : : * TransamVariables->oldestXid as input.
2471 : : *
2472 : : * We should definitely be able to do better. We could e.g. put a
2473 : : * global lower bound value into TransamVariables.
2474 : : */
2475 : : GlobalVisSharedRels.maybe_needed =
1341 2476 : 386199 : FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
2477 : : oldestfxid);
2478 : : GlobalVisCatalogRels.maybe_needed =
2479 : 386199 : FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
2480 : : oldestfxid);
2481 : : GlobalVisDataRels.maybe_needed =
2482 : 386199 : FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
2483 : : oldestfxid);
2484 : : /* accurate value known */
1264 2485 : 386199 : GlobalVisTempRels.maybe_needed = GlobalVisTempRels.definitely_needed;
2486 : : }
2487 : :
6905 tgl@sss.pgh.pa.us 2488 : 386199 : RecentXmin = xmin;
1339 andres@anarazel.de 2489 [ - + ]: 386199 : Assert(TransactionIdPrecedesOrEquals(TransactionXmin, RecentXmin));
2490 : :
6905 tgl@sss.pgh.pa.us 2491 : 386199 : snapshot->xmin = xmin;
2492 : 386199 : snapshot->xmax = xmax;
2493 : 386199 : snapshot->xcnt = count;
6433 2494 : 386199 : snapshot->subxcnt = subcount;
5230 simon@2ndQuadrant.co 2495 : 386199 : snapshot->suboverflowed = suboverflowed;
1336 andres@anarazel.de 2496 : 386199 : snapshot->snapXactCompletionCount = curXactCompletionCount;
2497 : :
5980 tgl@sss.pgh.pa.us 2498 : 386199 : snapshot->curcid = GetCurrentCommandId(false);
2499 : :
2500 : : /*
2501 : : * This is a new snapshot, so set both refcounts are zero, and mark it as
2502 : : * not copied in persistent memory.
2503 : : */
5816 alvherre@alvh.no-ip. 2504 : 386199 : snapshot->active_count = 0;
2505 : 386199 : snapshot->regd_count = 0;
2506 : 386199 : snapshot->copied = false;
222 tmunro@postgresql.or 2507 :GNC 386199 : snapshot->lsn = InvalidXLogRecPtr;
2508 : 386199 : snapshot->whenTaken = 0;
2509 : :
6905 tgl@sss.pgh.pa.us 2510 :CBC 386199 : return snapshot;
2511 : : }
2512 : :
2513 : : /*
2514 : : * ProcArrayInstallImportedXmin -- install imported xmin into MyProc->xmin
2515 : : *
2516 : : * This is called when installing a snapshot imported from another
2517 : : * transaction. To ensure that OldestXmin doesn't go backwards, we must
2518 : : * check that the source transaction is still running, and we'd better do
2519 : : * that atomically with installing the new xmin.
2520 : : *
2521 : : * Returns true if successful, false if source xact is no longer running.
2522 : : */
2523 : : bool
2496 andres@anarazel.de 2524 : 18 : ProcArrayInstallImportedXmin(TransactionId xmin,
2525 : : VirtualTransactionId *sourcevxid)
2526 : : {
4558 tgl@sss.pgh.pa.us 2527 : 18 : bool result = false;
2528 : 18 : ProcArrayStruct *arrayP = procArray;
2529 : : int index;
2530 : :
2531 [ - + ]: 18 : Assert(TransactionIdIsNormal(xmin));
2496 andres@anarazel.de 2532 [ - + ]: 18 : if (!sourcevxid)
4558 tgl@sss.pgh.pa.us 2533 :UBC 0 : return false;
2534 : :
2535 : : /* Get lock so source xact can't end while we're doing this */
4558 tgl@sss.pgh.pa.us 2536 :CBC 18 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2537 : :
2538 : : /*
2539 : : * Find the PGPROC entry of the source transaction. (This could use
2540 : : * GetPGProcByNumber(), unless it's a prepared xact. But this isn't
2541 : : * performance critical.)
2542 : : */
2543 [ + - ]: 18 : for (index = 0; index < arrayP->numProcs; index++)
2544 : : {
4326 bruce@momjian.us 2545 : 18 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 2546 : 18 : PGPROC *proc = &allProcs[pgprocno];
1245 alvherre@alvh.no-ip. 2547 : 18 : int statusFlags = ProcGlobal->statusFlags[index];
2548 : : TransactionId xid;
2549 : :
2550 : : /* Ignore procs running LAZY VACUUM */
2551 [ - + ]: 18 : if (statusFlags & PROC_IN_VACUUM)
4558 tgl@sss.pgh.pa.us 2552 :UBC 0 : continue;
2553 : :
2554 : : /* We are only interested in the specific virtual transaction. */
42 heikki.linnakangas@i 2555 [ - + ]:GNC 18 : if (proc->vxid.procNumber != sourcevxid->procNumber)
2496 andres@anarazel.de 2556 :LBC (35) : continue;
42 heikki.linnakangas@i 2557 [ - + ]:GNC 18 : if (proc->vxid.lxid != sourcevxid->localTransactionId)
4558 tgl@sss.pgh.pa.us 2558 :UBC 0 : continue;
2559 : :
2560 : : /*
2561 : : * We check the transaction's database ID for paranoia's sake: if it's
2562 : : * in another DB then its xmin does not cover us. Caller should have
2563 : : * detected this already, so we just treat any funny cases as
2564 : : * "transaction not found".
2565 : : */
4558 tgl@sss.pgh.pa.us 2566 [ - + ]:CBC 18 : if (proc->databaseId != MyDatabaseId)
4558 tgl@sss.pgh.pa.us 2567 :UBC 0 : continue;
2568 : :
2569 : : /*
2570 : : * Likewise, let's just make real sure its xmin does cover us.
2571 : : */
1340 andres@anarazel.de 2572 :CBC 18 : xid = UINT32_ACCESS_ONCE(proc->xmin);
4558 tgl@sss.pgh.pa.us 2573 [ + - ]: 18 : if (!TransactionIdIsNormal(xid) ||
2574 [ - + ]: 18 : !TransactionIdPrecedesOrEquals(xid, xmin))
4558 tgl@sss.pgh.pa.us 2575 :UBC 0 : continue;
2576 : :
2577 : : /*
2578 : : * We're good. Install the new xmin. As in GetSnapshotData, set
2579 : : * TransactionXmin too. (Note that because snapmgr.c called
2580 : : * GetSnapshotData first, we'll be overwriting a valid xmin here, so
2581 : : * we don't check that.)
2582 : : */
1340 andres@anarazel.de 2583 :CBC 18 : MyProc->xmin = TransactionXmin = xmin;
2584 : :
4558 tgl@sss.pgh.pa.us 2585 : 18 : result = true;
2586 : 18 : break;
2587 : : }
2588 : :
2589 : 18 : LWLockRelease(ProcArrayLock);
2590 : :
2591 : 18 : return result;
2592 : : }
2593 : :
2594 : : /*
2595 : : * ProcArrayInstallRestoredXmin -- install restored xmin into MyProc->xmin
2596 : : *
2597 : : * This is like ProcArrayInstallImportedXmin, but we have a pointer to the
2598 : : * PGPROC of the transaction from which we imported the snapshot, rather than
2599 : : * an XID.
2600 : : *
2601 : : * Note that this function also copies statusFlags from the source `proc` in
2602 : : * order to avoid the case where MyProc's xmin needs to be skipped for
2603 : : * computing xid horizon.
2604 : : *
2605 : : * Returns true if successful, false if source xact is no longer running.
2606 : : */
2607 : : bool
3272 rhaas@postgresql.org 2608 : 1491 : ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
2609 : : {
2610 : 1491 : bool result = false;
2611 : : TransactionId xid;
2612 : :
2613 [ - + ]: 1491 : Assert(TransactionIdIsNormal(xmin));
2614 [ - + ]: 1491 : Assert(proc != NULL);
2615 : :
2616 : : /*
2617 : : * Get an exclusive lock so that we can copy statusFlags from source proc.
2618 : : */
877 akapila@postgresql.o 2619 : 1491 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
2620 : :
2621 : : /*
2622 : : * Be certain that the referenced PGPROC has an advertised xmin which is
2623 : : * no later than the one we're installing, so that the system-wide xmin
2624 : : * can't go backwards. Also, make sure it's running in the same database,
2625 : : * so that the per-database xmin cannot go backwards.
2626 : : */
1340 andres@anarazel.de 2627 : 1491 : xid = UINT32_ACCESS_ONCE(proc->xmin);
3272 rhaas@postgresql.org 2628 [ + - + - ]: 1491 : if (proc->databaseId == MyDatabaseId &&
2629 [ + - ]: 1491 : TransactionIdIsNormal(xid) &&
2630 : 1491 : TransactionIdPrecedesOrEquals(xid, xmin))
2631 : : {
2632 : : /*
2633 : : * Install xmin and propagate the statusFlags that affect how the
2634 : : * value is interpreted by vacuum.
2635 : : */
1340 andres@anarazel.de 2636 : 1491 : MyProc->xmin = TransactionXmin = xmin;
696 alvherre@alvh.no-ip. 2637 : 1491 : MyProc->statusFlags = (MyProc->statusFlags & ~PROC_XMIN_FLAGS) |
2638 : 1491 : (proc->statusFlags & PROC_XMIN_FLAGS);
2639 : 1491 : ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags;
2640 : :
3272 rhaas@postgresql.org 2641 : 1491 : result = true;
2642 : : }
2643 : :
2644 : 1491 : LWLockRelease(ProcArrayLock);
2645 : :
2646 : 1491 : return result;
2647 : : }
2648 : :
2649 : : /*
2650 : : * GetRunningTransactionData -- returns information about running transactions.
2651 : : *
2652 : : * Similar to GetSnapshotData but returns more information. We include
2653 : : * all PGPROCs with an assigned TransactionId, even VACUUM processes and
2654 : : * prepared transactions.
2655 : : *
2656 : : * We acquire XidGenLock and ProcArrayLock, but the caller is responsible for
2657 : : * releasing them. Acquiring XidGenLock ensures that no new XIDs enter the proc
2658 : : * array until the caller has WAL-logged this snapshot, and releases the
2659 : : * lock. Acquiring ProcArrayLock ensures that no transactions commit until the
2660 : : * lock is released.
2661 : : *
2662 : : * The returned data structure is statically allocated; caller should not
2663 : : * modify it, and must not assume it is valid past the next call.
2664 : : *
2665 : : * This is never executed during recovery so there is no need to look at
2666 : : * KnownAssignedXids.
2667 : : *
2668 : : * Dummy PGPROCs from prepared transaction are included, meaning that this
2669 : : * may return entries with duplicated TransactionId values coming from
2670 : : * transaction finishing to prepare. Nothing is done about duplicated
2671 : : * entries here to not hold on ProcArrayLock more than necessary.
2672 : : *
2673 : : * We don't worry about updating other counters, we want to keep this as
2674 : : * simple as possible and leave GetSnapshotData() as the primary code for
2675 : : * that bookkeeping.
2676 : : *
2677 : : * Note that if any transaction has overflowed its cached subtransactions
2678 : : * then there is no real need include any subtransactions.
2679 : : */
2680 : : RunningTransactions
5230 simon@2ndQuadrant.co 2681 : 953 : GetRunningTransactionData(void)
2682 : : {
2683 : : /* result workspace */
2684 : : static RunningTransactionsData CurrentRunningXactsData;
2685 : :
2686 : 953 : ProcArrayStruct *arrayP = procArray;
1339 andres@anarazel.de 2687 : 953 : TransactionId *other_xids = ProcGlobal->xids;
5100 tgl@sss.pgh.pa.us 2688 : 953 : RunningTransactions CurrentRunningXacts = &CurrentRunningXactsData;
2689 : : TransactionId latestCompletedXid;
2690 : : TransactionId oldestRunningXid;
2691 : : TransactionId oldestDatabaseRunningXid;
2692 : : TransactionId *xids;
2693 : : int index;
2694 : : int count;
2695 : : int subcount;
2696 : : bool suboverflowed;
2697 : :
5230 simon@2ndQuadrant.co 2698 [ - + ]: 953 : Assert(!RecoveryInProgress());
2699 : :
2700 : : /*
2701 : : * Allocating space for maxProcs xids is usually overkill; numProcs would
2702 : : * be sufficient. But it seems better to do the malloc while not holding
2703 : : * the lock, so we can't look at numProcs. Likewise, we allocate much
2704 : : * more subxip storage than is probably needed.
2705 : : *
2706 : : * Should only be allocated in bgwriter, since only ever executed during
2707 : : * checkpoints.
2708 : : */
2709 [ + + ]: 953 : if (CurrentRunningXacts->xids == NULL)
2710 : : {
2711 : : /*
2712 : : * First call
2713 : : */
2714 : 542 : CurrentRunningXacts->xids = (TransactionId *)
2715 : 542 : malloc(TOTAL_MAX_CACHED_SUBXIDS * sizeof(TransactionId));
2716 [ - + ]: 542 : if (CurrentRunningXacts->xids == NULL)
5230 simon@2ndQuadrant.co 2717 [ # # ]:UBC 0 : ereport(ERROR,
2718 : : (errcode(ERRCODE_OUT_OF_MEMORY),
2719 : : errmsg("out of memory")));
2720 : : }
2721 : :
5230 simon@2ndQuadrant.co 2722 :CBC 953 : xids = CurrentRunningXacts->xids;
2723 : :
2724 : 953 : count = subcount = 0;
2725 : 953 : suboverflowed = false;
2726 : :
2727 : : /*
2728 : : * Ensure that no xids enter or leave the procarray while we obtain
2729 : : * snapshot.
2730 : : */
2731 : 953 : LWLockAcquire(ProcArrayLock, LW_SHARED);
2732 : 953 : LWLockAcquire(XidGenLock, LW_SHARED);
2733 : :
1342 andres@anarazel.de 2734 : 953 : latestCompletedXid =
128 heikki.linnakangas@i 2735 :GNC 953 : XidFromFullTransactionId(TransamVariables->latestCompletedXid);
31 akorotkov@postgresql 2736 : 953 : oldestDatabaseRunningXid = oldestRunningXid =
128 heikki.linnakangas@i 2737 : 953 : XidFromFullTransactionId(TransamVariables->nextXid);
2738 : :
2739 : : /*
2740 : : * Spin over procArray collecting all xids
2741 : : */
5230 simon@2ndQuadrant.co 2742 [ + + ]:CBC 4115 : for (index = 0; index < arrayP->numProcs; index++)
2743 : : {
31 akorotkov@postgresql 2744 :GNC 3162 : int pgprocno = arrayP->pgprocnos[index];
2745 : 3162 : PGPROC *proc = &allProcs[pgprocno];
2746 : : TransactionId xid;
2747 : :
2748 : : /* Fetch xid just once - see GetNewTransactionId */
1339 andres@anarazel.de 2749 :CBC 3162 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2750 : :
2751 : : /*
2752 : : * We don't need to store transactions that don't have a TransactionId
2753 : : * yet because they will not show as running on a standby server.
2754 : : */
5230 simon@2ndQuadrant.co 2755 [ + + ]: 3162 : if (!TransactionIdIsValid(xid))
2756 : 2854 : continue;
2757 : :
2758 : : /*
2759 : : * Be careful not to exclude any xids before calculating the values of
2760 : : * oldestRunningXid and suboverflowed, since these are used to clean
2761 : : * up transaction information held on standbys.
2762 : : */
2763 [ + + ]: 308 : if (TransactionIdPrecedes(xid, oldestRunningXid))
2764 : 288 : oldestRunningXid = xid;
2765 : :
2766 : : /*
2767 : : * Also, update the oldest running xid within the current database.
2768 : : */
31 akorotkov@postgresql 2769 [ + + - + ]:GNC 472 : if (proc->databaseId == MyDatabaseId &&
2770 : 164 : TransactionIdPrecedes(xid, oldestRunningXid))
31 akorotkov@postgresql 2771 :UNC 0 : oldestDatabaseRunningXid = xid;
2772 : :
1339 andres@anarazel.de 2773 [ + + ]:CBC 308 : if (ProcGlobal->subxidStates[index].overflowed)
4151 simon@2ndQuadrant.co 2774 : 2 : suboverflowed = true;
2775 : :
2776 : : /*
2777 : : * If we wished to exclude xids this would be the right place for it.
2778 : : * Procs with the PROC_IN_VACUUM flag set don't usually assign xids,
2779 : : * but they do during truncation at the end when they get the lock and
2780 : : * truncate, so it is not much of a problem to include them if they
2781 : : * are seen and it is cleaner to include them.
2782 : : */
2783 : :
2131 2784 : 308 : xids[count++] = xid;
2785 : : }
2786 : :
2787 : : /*
2788 : : * Spin over procArray collecting all subxids, but only if there hasn't
2789 : : * been a suboverflow.
2790 : : */
4151 2791 [ + + ]: 953 : if (!suboverflowed)
2792 : : {
1339 andres@anarazel.de 2793 : 951 : XidCacheStatus *other_subxidstates = ProcGlobal->subxidStates;
2794 : :
4151 simon@2ndQuadrant.co 2795 [ + + ]: 4109 : for (index = 0; index < arrayP->numProcs; index++)
2796 : : {
2797 : 3158 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 2798 : 3158 : PGPROC *proc = &allProcs[pgprocno];
2799 : : int nsubxids;
2800 : :
2801 : : /*
2802 : : * Save subtransaction XIDs. Other backends can't add or remove
2803 : : * entries while we're holding XidGenLock.
2804 : : */
1339 2805 : 3158 : nsubxids = other_subxidstates[index].count;
2806 [ + + ]: 3158 : if (nsubxids > 0)
2807 : : {
2808 : : /* barrier not really required, as XidGenLock is held, but ... */
1983 2809 : 7 : pg_read_barrier(); /* pairs with GetNewTransactionId */
2810 : :
432 peter@eisentraut.org 2811 : 7 : memcpy(&xids[count], proc->subxids.xids,
2812 : : nsubxids * sizeof(TransactionId));
1339 andres@anarazel.de 2813 : 7 : count += nsubxids;
2814 : 7 : subcount += nsubxids;
2815 : :
2816 : : /*
2817 : : * Top-level XID of a transaction is always less than any of
2818 : : * its subxids, so we don't need to check if any of the
2819 : : * subxids are smaller than oldestRunningXid
2820 : : */
2821 : : }
2822 : : }
2823 : : }
2824 : :
2825 : : /*
2826 : : * It's important *not* to include the limits set by slots here because
2827 : : * snapbuild.c uses oldestRunningXid to manage its xmin horizon. If those
2828 : : * were to be included here the initial value could never increase because
2829 : : * of a circular dependency where slots only increase their limits when
2830 : : * running xacts increases oldestRunningXid and running xacts only
2831 : : * increases if slots do.
2832 : : */
2833 : :
4151 simon@2ndQuadrant.co 2834 : 953 : CurrentRunningXacts->xcnt = count - subcount;
2835 : 953 : CurrentRunningXacts->subxcnt = subcount;
5230 2836 : 953 : CurrentRunningXacts->subxid_overflow = suboverflowed;
128 heikki.linnakangas@i 2837 :GNC 953 : CurrentRunningXacts->nextXid = XidFromFullTransactionId(TransamVariables->nextXid);
5230 simon@2ndQuadrant.co 2838 :CBC 953 : CurrentRunningXacts->oldestRunningXid = oldestRunningXid;
31 akorotkov@postgresql 2839 :GNC 953 : CurrentRunningXacts->oldestDatabaseRunningXid = oldestDatabaseRunningXid;
5085 simon@2ndQuadrant.co 2840 :CBC 953 : CurrentRunningXacts->latestCompletedXid = latestCompletedXid;
2841 : :
5084 2842 [ - + ]: 953 : Assert(TransactionIdIsValid(CurrentRunningXacts->nextXid));
2843 [ - + ]: 953 : Assert(TransactionIdIsValid(CurrentRunningXacts->oldestRunningXid));
2844 [ - + ]: 953 : Assert(TransactionIdIsNormal(CurrentRunningXacts->latestCompletedXid));
2845 : :
2846 : : /* We don't release the locks here, the caller is responsible for that */
2847 : :
5230 2848 : 953 : return CurrentRunningXacts;
2849 : : }
2850 : :
2851 : : /*
2852 : : * GetOldestActiveTransactionId()
2853 : : *
2854 : : * Similar to GetSnapshotData but returns just oldestActiveXid. We include
2855 : : * all PGPROCs with an assigned TransactionId, even VACUUM processes.
2856 : : * We look at all databases, though there is no need to include WALSender
2857 : : * since this has no effect on hot standby conflicts.
2858 : : *
2859 : : * This is never executed during recovery so there is no need to look at
2860 : : * KnownAssignedXids.
2861 : : *
2862 : : * We don't worry about updating other counters, we want to keep this as
2863 : : * simple as possible and leave GetSnapshotData() as the primary code for
2864 : : * that bookkeeping.
2865 : : */
2866 : : TransactionId
4547 2867 : 490 : GetOldestActiveTransactionId(void)
2868 : : {
2869 : 490 : ProcArrayStruct *arrayP = procArray;
1339 andres@anarazel.de 2870 : 490 : TransactionId *other_xids = ProcGlobal->xids;
2871 : : TransactionId oldestRunningXid;
2872 : : int index;
2873 : :
4547 simon@2ndQuadrant.co 2874 [ - + ]: 490 : Assert(!RecoveryInProgress());
2875 : :
2876 : : /*
2877 : : * Read nextXid, as the upper bound of what's still active.
2878 : : *
2879 : : * Reading a TransactionId is atomic, but we must grab the lock to make
2880 : : * sure that all XIDs < nextXid are already present in the proc array (or
2881 : : * have already completed), when we spin over it.
2882 : : */
2467 heikki.linnakangas@i 2883 : 490 : LWLockAcquire(XidGenLock, LW_SHARED);
128 heikki.linnakangas@i 2884 :GNC 490 : oldestRunningXid = XidFromFullTransactionId(TransamVariables->nextXid);
2467 heikki.linnakangas@i 2885 :CBC 490 : LWLockRelease(XidGenLock);
2886 : :
2887 : : /*
2888 : : * Spin over procArray collecting all xids and subxids.
2889 : : */
2890 : 490 : LWLockAcquire(ProcArrayLock, LW_SHARED);
4547 simon@2ndQuadrant.co 2891 [ + + ]: 1739 : for (index = 0; index < arrayP->numProcs; index++)
2892 : : {
2893 : : TransactionId xid;
2894 : :
2895 : : /* Fetch xid just once - see GetNewTransactionId */
1339 andres@anarazel.de 2896 : 1249 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2897 : :
4547 simon@2ndQuadrant.co 2898 [ + + ]: 1249 : if (!TransactionIdIsNormal(xid))
2899 : 986 : continue;
2900 : :
2901 [ + + ]: 263 : if (TransactionIdPrecedes(xid, oldestRunningXid))
2902 : 245 : oldestRunningXid = xid;
2903 : :
2904 : : /*
2905 : : * Top-level XID of a transaction is always less than any of its
2906 : : * subxids, so we don't need to check if any of the subxids are
2907 : : * smaller than oldestRunningXid
2908 : : */
2909 : : }
2910 : 490 : LWLockRelease(ProcArrayLock);
2911 : :
2912 : 490 : return oldestRunningXid;
2913 : : }
2914 : :
2915 : : /*
2916 : : * GetOldestSafeDecodingTransactionId -- lowest xid not affected by vacuum
2917 : : *
2918 : : * Returns the oldest xid that we can guarantee not to have been affected by
2919 : : * vacuum, i.e. no rows >= that xid have been vacuumed away unless the
2920 : : * transaction aborted. Note that the value can (and most of the time will) be
2921 : : * much more conservative than what really has been affected by vacuum, but we
2922 : : * currently don't have better data available.
2923 : : *
2924 : : * This is useful to initialize the cutoff xid after which a new changeset
2925 : : * extraction replication slot can start decoding changes.
2926 : : *
2927 : : * Must be called with ProcArrayLock held either shared or exclusively,
2928 : : * although most callers will want to use exclusive mode since it is expected
2929 : : * that the caller will immediately use the xid to peg the xmin horizon.
2930 : : */
2931 : : TransactionId
2548 andres@anarazel.de 2932 : 569 : GetOldestSafeDecodingTransactionId(bool catalogOnly)
2933 : : {
3695 rhaas@postgresql.org 2934 : 569 : ProcArrayStruct *arrayP = procArray;
2935 : : TransactionId oldestSafeXid;
2936 : : int index;
2937 : 569 : bool recovery_in_progress = RecoveryInProgress();
2938 : :
2939 [ - + ]: 569 : Assert(LWLockHeldByMe(ProcArrayLock));
2940 : :
2941 : : /*
2942 : : * Acquire XidGenLock, so no transactions can acquire an xid while we're
2943 : : * running. If no transaction with xid were running concurrently a new xid
2944 : : * could influence the RecentXmin et al.
2945 : : *
2946 : : * We initialize the computation to nextXid since that's guaranteed to be
2947 : : * a safe, albeit pessimal, value.
2948 : : */
2949 : 569 : LWLockAcquire(XidGenLock, LW_SHARED);
128 heikki.linnakangas@i 2950 :GNC 569 : oldestSafeXid = XidFromFullTransactionId(TransamVariables->nextXid);
2951 : :
2952 : : /*
2953 : : * If there's already a slot pegging the xmin horizon, we can start with
2954 : : * that value, it's guaranteed to be safe since it's computed by this
2955 : : * routine initially and has been enforced since. We can always use the
2956 : : * slot's general xmin horizon, but the catalog horizon is only usable
2957 : : * when only catalog data is going to be looked at.
2958 : : */
2548 andres@anarazel.de 2959 [ + + + + ]:CBC 756 : if (TransactionIdIsValid(procArray->replication_slot_xmin) &&
2960 : 187 : TransactionIdPrecedes(procArray->replication_slot_xmin,
2961 : : oldestSafeXid))
2962 : 9 : oldestSafeXid = procArray->replication_slot_xmin;
2963 : :
2964 [ + + ]: 569 : if (catalogOnly &&
2965 [ + + + + ]: 292 : TransactionIdIsValid(procArray->replication_slot_catalog_xmin) &&
3695 rhaas@postgresql.org 2966 : 61 : TransactionIdPrecedes(procArray->replication_slot_catalog_xmin,
2967 : : oldestSafeXid))
2968 : 23 : oldestSafeXid = procArray->replication_slot_catalog_xmin;
2969 : :
2970 : : /*
2971 : : * If we're not in recovery, we walk over the procarray and collect the
2972 : : * lowest xid. Since we're called with ProcArrayLock held and have
2973 : : * acquired XidGenLock, no entries can vanish concurrently, since
2974 : : * ProcGlobal->xids[i] is only set with XidGenLock held and only cleared
2975 : : * with ProcArrayLock held.
2976 : : *
2977 : : * In recovery we can't lower the safe value besides what we've computed
2978 : : * above, so we'll have to wait a bit longer there. We unfortunately can
2979 : : * *not* use KnownAssignedXidsGetOldestXmin() since the KnownAssignedXids
2980 : : * machinery can miss values and return an older value than is safe.
2981 : : */
2982 [ + + ]: 569 : if (!recovery_in_progress)
2983 : : {
1339 andres@anarazel.de 2984 : 543 : TransactionId *other_xids = ProcGlobal->xids;
2985 : :
2986 : : /*
2987 : : * Spin over procArray collecting min(ProcGlobal->xids[i])
2988 : : */
3695 rhaas@postgresql.org 2989 [ + + ]: 2839 : for (index = 0; index < arrayP->numProcs; index++)
2990 : : {
2991 : : TransactionId xid;
2992 : :
2993 : : /* Fetch xid just once - see GetNewTransactionId */
1339 andres@anarazel.de 2994 : 2296 : xid = UINT32_ACCESS_ONCE(other_xids[index]);
2995 : :
3695 rhaas@postgresql.org 2996 [ + + ]: 2296 : if (!TransactionIdIsNormal(xid))
2997 : 2285 : continue;
2998 : :
2999 [ + + ]: 11 : if (TransactionIdPrecedes(xid, oldestSafeXid))
3000 : 9 : oldestSafeXid = xid;
3001 : : }
3002 : : }
3003 : :
3004 : 569 : LWLockRelease(XidGenLock);
3005 : :
3006 : 569 : return oldestSafeXid;
3007 : : }
3008 : :
3009 : : /*
3010 : : * GetVirtualXIDsDelayingChkpt -- Get the VXIDs of transactions that are
3011 : : * delaying checkpoint because they have critical actions in progress.
3012 : : *
3013 : : * Constructs an array of VXIDs of transactions that are currently in commit
3014 : : * critical sections, as shown by having specified delayChkptFlags bits set
3015 : : * in their PGPROC.
3016 : : *
3017 : : * Returns a palloc'd array that should be freed by the caller.
3018 : : * *nvxids is the number of valid entries.
3019 : : *
3020 : : * Note that because backends set or clear delayChkptFlags without holding any
3021 : : * lock, the result is somewhat indeterminate, but we don't really care. Even
3022 : : * in a multiprocessor with delayed writes to shared memory, it should be
3023 : : * certain that setting of delayChkptFlags will propagate to shared memory
3024 : : * when the backend takes a lock, so we cannot fail to see a virtual xact as
3025 : : * delayChkptFlags if it's already inserted its commit record. Whether it
3026 : : * takes a little while for clearing of delayChkptFlags to propagate is
3027 : : * unimportant for correctness.
3028 : : */
3029 : : VirtualTransactionId *
752 3030 : 2205 : GetVirtualXIDsDelayingChkpt(int *nvxids, int type)
3031 : : {
3032 : : VirtualTransactionId *vxids;
6221 tgl@sss.pgh.pa.us 3033 : 2205 : ProcArrayStruct *arrayP = procArray;
4150 simon@2ndQuadrant.co 3034 : 2205 : int count = 0;
3035 : : int index;
3036 : :
752 rhaas@postgresql.org 3037 [ - + ]: 2205 : Assert(type != 0);
3038 : :
3039 : : /* allocate what's certainly enough result space */
3040 : : vxids = (VirtualTransactionId *)
4150 simon@2ndQuadrant.co 3041 : 2205 : palloc(sizeof(VirtualTransactionId) * arrayP->maxProcs);
3042 : :
6221 tgl@sss.pgh.pa.us 3043 : 2205 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3044 : :
3045 [ + + ]: 5369 : for (index = 0; index < arrayP->numProcs; index++)
3046 : : {
3973 bruce@momjian.us 3047 : 3164 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3048 : 3164 : PGPROC *proc = &allProcs[pgprocno];
3049 : :
737 rhaas@postgresql.org 3050 [ + + ]: 3164 : if ((proc->delayChkptFlags & type) != 0)
3051 : : {
3052 : : VirtualTransactionId vxid;
3053 : :
4150 simon@2ndQuadrant.co 3054 : 2 : GET_VXID_FROM_PGPROC(vxid, *proc);
3055 [ + - ]: 2 : if (VirtualTransactionIdIsValid(vxid))
3056 : 2 : vxids[count++] = vxid;
3057 : : }
3058 : : }
3059 : :
6221 tgl@sss.pgh.pa.us 3060 : 2205 : LWLockRelease(ProcArrayLock);
3061 : :
4150 simon@2ndQuadrant.co 3062 : 2205 : *nvxids = count;
3063 : 2205 : return vxids;
3064 : : }
3065 : :
3066 : : /*
3067 : : * HaveVirtualXIDsDelayingChkpt -- Are any of the specified VXIDs delaying?
3068 : : *
3069 : : * This is used with the results of GetVirtualXIDsDelayingChkpt to see if any
3070 : : * of the specified VXIDs are still in critical sections of code.
3071 : : *
3072 : : * Note: this is O(N^2) in the number of vxacts that are/were delaying, but
3073 : : * those numbers should be small enough for it not to be a problem.
3074 : : */
3075 : : bool
752 rhaas@postgresql.org 3076 : 1 : HaveVirtualXIDsDelayingChkpt(VirtualTransactionId *vxids, int nvxids, int type)
3077 : : {
5995 bruce@momjian.us 3078 : 1 : bool result = false;
6221 tgl@sss.pgh.pa.us 3079 : 1 : ProcArrayStruct *arrayP = procArray;
3080 : : int index;
3081 : :
752 rhaas@postgresql.org 3082 [ - + ]: 1 : Assert(type != 0);
3083 : :
6221 tgl@sss.pgh.pa.us 3084 : 1 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3085 : :
3959 noah@leadboat.com 3086 [ + + ]: 12 : for (index = 0; index < arrayP->numProcs; index++)
3087 : : {
3088 : 11 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3089 : 11 : PGPROC *proc = &allProcs[pgprocno];
3090 : : VirtualTransactionId vxid;
3091 : :
3959 noah@leadboat.com 3092 : 11 : GET_VXID_FROM_PGPROC(vxid, *proc);
3093 : :
737 rhaas@postgresql.org 3094 [ + + ]: 11 : if ((proc->delayChkptFlags & type) != 0 &&
752 3095 [ + - ]: 2 : VirtualTransactionIdIsValid(vxid))
3096 : : {
3097 : : int i;
3098 : :
3959 noah@leadboat.com 3099 [ + + ]: 6 : for (i = 0; i < nvxids; i++)
3100 : : {
3101 [ - + - - ]: 4 : if (VirtualTransactionIdEquals(vxid, vxids[i]))
3102 : : {
6221 tgl@sss.pgh.pa.us 3103 :UBC 0 : result = true;
3104 : 0 : break;
3105 : : }
3106 : : }
3959 noah@leadboat.com 3107 [ - + ]:CBC 2 : if (result)
3959 noah@leadboat.com 3108 :UBC 0 : break;
3109 : : }
3110 : : }
3111 : :
6221 tgl@sss.pgh.pa.us 3112 :CBC 1 : LWLockRelease(ProcArrayLock);
3113 : :
3114 : 1 : return result;
3115 : : }
3116 : :
3117 : : /*
3118 : : * ProcNumberGetProc -- get a backend's PGPROC given its proc number
3119 : : *
3120 : : * The result may be out of date arbitrarily quickly, so the caller
3121 : : * must be careful about how this information is used. NULL is
3122 : : * returned if the backend is not active.
3123 : : */
3124 : : PGPROC *
42 heikki.linnakangas@i 3125 :GNC 544 : ProcNumberGetProc(ProcNumber procNumber)
3126 : : {
3127 : : PGPROC *result;
3128 : :
3129 [ + + - + ]: 544 : if (procNumber < 0 || procNumber >= ProcGlobal->allProcCount)
3130 : 1 : return NULL;
3131 : 543 : result = GetPGProcByNumber(procNumber);
3132 : :
3133 [ + + ]: 543 : if (result->pid == 0)
3134 : 3 : return NULL;
3135 : :
3136 : 540 : return result;
3137 : : }
3138 : :
3139 : : /*
3140 : : * ProcNumberGetTransactionIds -- get a backend's transaction status
3141 : : *
3142 : : * Get the xid, xmin, nsubxid and overflow status of the backend. The
3143 : : * result may be out of date arbitrarily quickly, so the caller must be
3144 : : * careful about how this information is used.
3145 : : */
3146 : : void
3147 : 7285 : ProcNumberGetTransactionIds(ProcNumber procNumber, TransactionId *xid,
3148 : : TransactionId *xmin, int *nsubxid, bool *overflowed)
3149 : : {
3150 : : PGPROC *proc;
3151 : :
3152 : 7285 : *xid = InvalidTransactionId;
3153 : 7285 : *xmin = InvalidTransactionId;
3154 : 7285 : *nsubxid = 0;
3155 : 7285 : *overflowed = false;
3156 : :
3157 [ + - - + ]: 7285 : if (procNumber < 0 || procNumber >= ProcGlobal->allProcCount)
42 heikki.linnakangas@i 3158 :UNC 0 : return;
42 heikki.linnakangas@i 3159 :GNC 7285 : proc = GetPGProcByNumber(procNumber);
3160 : :
3161 : : /* Need to lock out additions/removals of backends */
3162 : 7285 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3163 : :
3164 [ + - ]: 7285 : if (proc->pid != 0)
3165 : : {
3166 : 7285 : *xid = proc->xid;
3167 : 7285 : *xmin = proc->xmin;
3168 : 7285 : *nsubxid = proc->subxidStatus.count;
3169 : 7285 : *overflowed = proc->subxidStatus.overflowed;
3170 : : }
3171 : :
3172 : 7285 : LWLockRelease(ProcArrayLock);
3173 : : }
3174 : :
3175 : : /*
3176 : : * BackendPidGetProc -- get a backend's PGPROC given its PID
3177 : : *
3178 : : * Returns NULL if not found. Note that it is up to the caller to be
3179 : : * sure that the question remains meaningful for long enough for the
3180 : : * answer to be used ...
3181 : : */
3182 : : PGPROC *
6905 tgl@sss.pgh.pa.us 3183 :CBC 6101 : BackendPidGetProc(int pid)
3184 : : {
3185 : : PGPROC *result;
3186 : :
2974 3187 [ - + ]: 6101 : if (pid == 0) /* never match dummy PGPROCs */
2974 tgl@sss.pgh.pa.us 3188 :UBC 0 : return NULL;
3189 : :
2974 tgl@sss.pgh.pa.us 3190 :CBC 6101 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3191 : :
3192 : 6101 : result = BackendPidGetProcWithLock(pid);
3193 : :
3194 : 6101 : LWLockRelease(ProcArrayLock);
3195 : :
3196 : 6101 : return result;
3197 : : }
3198 : :
3199 : : /*
3200 : : * BackendPidGetProcWithLock -- get a backend's PGPROC given its PID
3201 : : *
3202 : : * Same as above, except caller must be holding ProcArrayLock. The found
3203 : : * entry, if any, can be assumed to be valid as long as the lock remains held.
3204 : : */
3205 : : PGPROC *
3206 : 8014 : BackendPidGetProcWithLock(int pid)
3207 : : {
6905 3208 : 8014 : PGPROC *result = NULL;
3209 : 8014 : ProcArrayStruct *arrayP = procArray;
3210 : : int index;
3211 : :
6876 3212 [ - + ]: 8014 : if (pid == 0) /* never match dummy PGPROCs */
6876 tgl@sss.pgh.pa.us 3213 :UBC 0 : return NULL;
3214 : :
6905 tgl@sss.pgh.pa.us 3215 [ + + ]:CBC 27316 : for (index = 0; index < arrayP->numProcs; index++)
3216 : : {
4524 rhaas@postgresql.org 3217 : 25004 : PGPROC *proc = &allProcs[arrayP->pgprocnos[index]];
3218 : :
6905 tgl@sss.pgh.pa.us 3219 [ + + ]: 25004 : if (proc->pid == pid)
3220 : : {
3221 : 5702 : result = proc;
3222 : 5702 : break;
3223 : : }
3224 : : }
3225 : :
3226 : 8014 : return result;
3227 : : }
3228 : :
3229 : : /*
3230 : : * BackendXidGetPid -- get a backend's pid given its XID
3231 : : *
3232 : : * Returns 0 if not found or it's a prepared transaction. Note that
3233 : : * it is up to the caller to be sure that the question remains
3234 : : * meaningful for long enough for the answer to be used ...
3235 : : *
3236 : : * Only main transaction Ids are considered. This function is mainly
3237 : : * useful for determining what backend owns a lock.
3238 : : *
3239 : : * Beware that not every xact has an XID assigned. However, as long as you
3240 : : * only call this using an XID found on disk, you're safe.
3241 : : */
3242 : : int
6812 ishii@postgresql.org 3243 : 30 : BackendXidGetPid(TransactionId xid)
3244 : : {
6756 bruce@momjian.us 3245 : 30 : int result = 0;
6812 ishii@postgresql.org 3246 : 30 : ProcArrayStruct *arrayP = procArray;
1339 andres@anarazel.de 3247 : 30 : TransactionId *other_xids = ProcGlobal->xids;
3248 : : int index;
3249 : :
6812 ishii@postgresql.org 3250 [ - + ]: 30 : if (xid == InvalidTransactionId) /* never match invalid xid */
6812 ishii@postgresql.org 3251 :UBC 0 : return 0;
3252 : :
6812 ishii@postgresql.org 3253 :CBC 30 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3254 : :
3255 [ + + ]: 92 : for (index = 0; index < arrayP->numProcs; index++)
3256 : : {
1339 andres@anarazel.de 3257 [ + + ]: 84 : if (other_xids[index] == xid)
3258 : : {
219 michael@paquier.xyz 3259 :GNC 22 : int pgprocno = arrayP->pgprocnos[index];
3260 : 22 : PGPROC *proc = &allProcs[pgprocno];
3261 : :
6812 ishii@postgresql.org 3262 :CBC 22 : result = proc->pid;
3263 : 22 : break;
3264 : : }
3265 : : }
3266 : :
3267 : 30 : LWLockRelease(ProcArrayLock);
3268 : :
3269 : 30 : return result;
3270 : : }
3271 : :
3272 : : /*
3273 : : * IsBackendPid -- is a given pid a running backend
3274 : : *
3275 : : * This is not called by the backend, but is called by external modules.
3276 : : */
3277 : : bool
6905 tgl@sss.pgh.pa.us 3278 : 2 : IsBackendPid(int pid)
3279 : : {
3280 : 2 : return (BackendPidGetProc(pid) != NULL);
3281 : : }
3282 : :
3283 : :
3284 : : /*
3285 : : * GetCurrentVirtualXIDs -- returns an array of currently active VXIDs.
3286 : : *
3287 : : * The array is palloc'd. The number of valid entries is returned into *nvxids.
3288 : : *
3289 : : * The arguments allow filtering the set of VXIDs returned. Our own process
3290 : : * is always skipped. In addition:
3291 : : * If limitXmin is not InvalidTransactionId, skip processes with
3292 : : * xmin > limitXmin.
3293 : : * If excludeXmin0 is true, skip processes with xmin = 0.
3294 : : * If allDbs is false, skip processes attached to other databases.
3295 : : * If excludeVacuum isn't zero, skip processes for which
3296 : : * (statusFlags & excludeVacuum) is not zero.
3297 : : *
3298 : : * Note: the purpose of the limitXmin and excludeXmin0 parameters is to
3299 : : * allow skipping backends whose oldest live snapshot is no older than
3300 : : * some snapshot we have. Since we examine the procarray with only shared
3301 : : * lock, there are race conditions: a backend could set its xmin just after
3302 : : * we look. Indeed, on multiprocessors with weak memory ordering, the
3303 : : * other backend could have set its xmin *before* we look. We know however
3304 : : * that such a backend must have held shared ProcArrayLock overlapping our
3305 : : * own hold of ProcArrayLock, else we would see its xmin update. Therefore,
3306 : : * any snapshot the other backend is taking concurrently with our scan cannot
3307 : : * consider any transactions as still running that we think are committed
3308 : : * (since backends must hold ProcArrayLock exclusive to commit).
3309 : : */
3310 : : VirtualTransactionId *
5489 3311 : 343 : GetCurrentVirtualXIDs(TransactionId limitXmin, bool excludeXmin0,
3312 : : bool allDbs, int excludeVacuum,
3313 : : int *nvxids)
3314 : : {
3315 : : VirtualTransactionId *vxids;
6066 3316 : 343 : ProcArrayStruct *arrayP = procArray;
3317 : 343 : int count = 0;
3318 : : int index;
3319 : :
3320 : : /* allocate what's certainly enough result space */
3321 : : vxids = (VirtualTransactionId *)
5489 3322 : 343 : palloc(sizeof(VirtualTransactionId) * arrayP->maxProcs);
3323 : :
6066 3324 : 343 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3325 : :
3326 [ + + ]: 2048 : for (index = 0; index < arrayP->numProcs; index++)
3327 : : {
4326 bruce@momjian.us 3328 : 1705 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3329 : 1705 : PGPROC *proc = &allProcs[pgprocno];
1245 alvherre@alvh.no-ip. 3330 : 1705 : uint8 statusFlags = ProcGlobal->statusFlags[index];
3331 : :
6066 tgl@sss.pgh.pa.us 3332 [ + + ]: 1705 : if (proc == MyProc)
3333 : 343 : continue;
3334 : :
1245 alvherre@alvh.no-ip. 3335 [ + + ]: 1362 : if (excludeVacuum & statusFlags)
5940 tgl@sss.pgh.pa.us 3336 : 8 : continue;
3337 : :
6064 3338 [ + - + + ]: 1354 : if (allDbs || proc->databaseId == MyDatabaseId)
3339 : : {
3340 : : /* Fetch xmin just once - might change on us */
1340 andres@anarazel.de 3341 : 603 : TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
3342 : :
5489 tgl@sss.pgh.pa.us 3343 [ + - + + ]: 603 : if (excludeXmin0 && !TransactionIdIsValid(pxmin))
3344 : 358 : continue;
3345 : :
3346 : : /*
3347 : : * InvalidTransactionId precedes all other XIDs, so a proc that
3348 : : * hasn't set xmin yet will not be rejected by this test.
3349 : : */
6064 3350 [ + - + + ]: 490 : if (!TransactionIdIsValid(limitXmin) ||
5489 3351 : 245 : TransactionIdPrecedesOrEquals(pxmin, limitXmin))
3352 : : {
3353 : : VirtualTransactionId vxid;
3354 : :
6064 3355 : 228 : GET_VXID_FROM_PGPROC(vxid, *proc);
3356 [ + - ]: 228 : if (VirtualTransactionIdIsValid(vxid))
3357 : 228 : vxids[count++] = vxid;
3358 : : }
3359 : : }
3360 : : }
3361 : :
6066 3362 : 343 : LWLockRelease(ProcArrayLock);
3363 : :
5489 3364 : 343 : *nvxids = count;
6066 3365 : 343 : return vxids;
3366 : : }
3367 : :
3368 : : /*
3369 : : * GetConflictingVirtualXIDs -- returns an array of currently active VXIDs.
3370 : : *
3371 : : * Usage is limited to conflict resolution during recovery on standby servers.
3372 : : * limitXmin is supplied as either a cutoff with snapshotConflictHorizon
3373 : : * semantics, or InvalidTransactionId in cases where caller cannot accurately
3374 : : * determine a safe snapshotConflictHorizon value.
3375 : : *
3376 : : * If limitXmin is InvalidTransactionId then we want to kill everybody,
3377 : : * so we're not worried if they have a snapshot or not, nor does it really
3378 : : * matter what type of lock we hold. Caller must avoid calling here with
3379 : : * snapshotConflictHorizon style cutoffs that were set to InvalidTransactionId
3380 : : * during original execution, since that actually indicates that there is
3381 : : * definitely no need for a recovery conflict (the snapshotConflictHorizon
3382 : : * convention for InvalidTransactionId values is the opposite of our own!).
3383 : : *
3384 : : * All callers that are checking xmins always now supply a valid and useful
3385 : : * value for limitXmin. The limitXmin is always lower than the lowest
3386 : : * numbered KnownAssignedXid that is not already a FATAL error. This is
3387 : : * because we only care about cleanup records that are cleaning up tuple
3388 : : * versions from committed transactions. In that case they will only occur
3389 : : * at the point where the record is less than the lowest running xid. That
3390 : : * allows us to say that if any backend takes a snapshot concurrently with
3391 : : * us then the conflict assessment made here would never include the snapshot
3392 : : * that is being derived. So we take LW_SHARED on the ProcArray and allow
3393 : : * concurrent snapshots when limitXmin is valid. We might think about adding
3394 : : * Assert(limitXmin < lowest(KnownAssignedXids))
3395 : : * but that would not be true in the case of FATAL errors lagging in array,
3396 : : * but we already know those are bogus anyway, so we skip that test.
3397 : : *
3398 : : * If dbOid is valid we skip backends attached to other databases.
3399 : : *
3400 : : * Be careful to *not* pfree the result from this function. We reuse
3401 : : * this array sufficiently often that we use malloc for the result.
3402 : : */
3403 : : VirtualTransactionId *
5195 simon@2ndQuadrant.co 3404 : 14140 : GetConflictingVirtualXIDs(TransactionId limitXmin, Oid dbOid)
3405 : : {
3406 : : static VirtualTransactionId *vxids;
5230 3407 : 14140 : ProcArrayStruct *arrayP = procArray;
3408 : 14140 : int count = 0;
3409 : : int index;
3410 : :
3411 : : /*
3412 : : * If first time through, get workspace to remember main XIDs in. We
3413 : : * malloc it permanently to avoid repeated palloc/pfree overhead. Allow
3414 : : * result space, remembering room for a terminator.
3415 : : */
3416 [ + + ]: 14140 : if (vxids == NULL)
3417 : : {
3418 : 28 : vxids = (VirtualTransactionId *)
3419 : 28 : malloc(sizeof(VirtualTransactionId) * (arrayP->maxProcs + 1));
3420 [ - + ]: 28 : if (vxids == NULL)
5230 simon@2ndQuadrant.co 3421 [ # # ]:UBC 0 : ereport(ERROR,
3422 : : (errcode(ERRCODE_OUT_OF_MEMORY),
3423 : : errmsg("out of memory")));
3424 : : }
3425 : :
5107 simon@2ndQuadrant.co 3426 :CBC 14140 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3427 : :
5230 3428 [ + + ]: 14288 : for (index = 0; index < arrayP->numProcs; index++)
3429 : : {
4326 bruce@momjian.us 3430 : 148 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3431 : 148 : PGPROC *proc = &allProcs[pgprocno];
3432 : :
3433 : : /* Exclude prepared transactions */
5230 simon@2ndQuadrant.co 3434 [ - + ]: 148 : if (proc->pid == 0)
5230 simon@2ndQuadrant.co 3435 :UBC 0 : continue;
3436 : :
5230 simon@2ndQuadrant.co 3437 [ + + ]:CBC 148 : if (!OidIsValid(dbOid) ||
3438 [ + + ]: 140 : proc->databaseId == dbOid)
3439 : : {
3440 : : /* Fetch xmin just once - can't change on us, but good coding */
1340 andres@anarazel.de 3441 : 18 : TransactionId pxmin = UINT32_ACCESS_ONCE(proc->xmin);
3442 : :
3443 : : /*
3444 : : * We ignore an invalid pxmin because this means that backend has
3445 : : * no snapshot currently. We hold a Share lock to avoid contention
3446 : : * with users taking snapshots. That is not a problem because the
3447 : : * current xmin is always at least one higher than the latest
3448 : : * removed xid, so any new snapshot would never conflict with the
3449 : : * test here.
3450 : : */
5107 simon@2ndQuadrant.co 3451 [ + + + + ]: 18 : if (!TransactionIdIsValid(limitXmin) ||
3452 [ + + ]: 4 : (TransactionIdIsValid(pxmin) && !TransactionIdFollows(pxmin, limitXmin)))
3453 : : {
3454 : : VirtualTransactionId vxid;
3455 : :
5230 simon@2ndQuadrant.co 3456 :GBC 2 : GET_VXID_FROM_PGPROC(vxid, *proc);
3457 [ + - ]: 2 : if (VirtualTransactionIdIsValid(vxid))
3458 : 2 : vxids[count++] = vxid;
3459 : : }
3460 : : }
3461 : : }
3462 : :
5230 simon@2ndQuadrant.co 3463 :CBC 14140 : LWLockRelease(ProcArrayLock);
3464 : :
3465 : : /* add the terminator */
42 heikki.linnakangas@i 3466 :GNC 14140 : vxids[count].procNumber = INVALID_PROC_NUMBER;
5230 simon@2ndQuadrant.co 3467 :CBC 14140 : vxids[count].localTransactionId = InvalidLocalTransactionId;
3468 : :
3469 : 14140 : return vxids;
3470 : : }
3471 : :
3472 : : /*
3473 : : * CancelVirtualTransaction - used in recovery conflict processing
3474 : : *
3475 : : * Returns pid of the process signaled, or 0 if not found.
3476 : : */
3477 : : pid_t
5202 simon@2ndQuadrant.co 3478 :GBC 3 : CancelVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode)
3479 : : {
1194 fujii@postgresql.org 3480 : 3 : return SignalVirtualTransaction(vxid, sigmode, true);
3481 : : }
3482 : :
3483 : : pid_t
3484 : 5 : SignalVirtualTransaction(VirtualTransactionId vxid, ProcSignalReason sigmode,
3485 : : bool conflictPending)
3486 : : {
5230 simon@2ndQuadrant.co 3487 : 5 : ProcArrayStruct *arrayP = procArray;
3488 : : int index;
3489 : 5 : pid_t pid = 0;
3490 : :
3491 : 5 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3492 : :
3493 [ + - ]: 5 : for (index = 0; index < arrayP->numProcs; index++)
3494 : : {
4326 bruce@momjian.us 3495 : 5 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3496 : 5 : PGPROC *proc = &allProcs[pgprocno];
3497 : : VirtualTransactionId procvxid;
3498 : :
5230 simon@2ndQuadrant.co 3499 : 5 : GET_VXID_FROM_PGPROC(procvxid, *proc);
3500 : :
42 heikki.linnakangas@i 3501 [ + - ]:GNC 5 : if (procvxid.procNumber == vxid.procNumber &&
5230 simon@2ndQuadrant.co 3502 [ + - ]:GBC 5 : procvxid.localTransactionId == vxid.localTransactionId)
3503 : : {
1194 fujii@postgresql.org 3504 : 5 : proc->recoveryConflictPending = conflictPending;
5230 simon@2ndQuadrant.co 3505 : 5 : pid = proc->pid;
5202 3506 [ + - ]: 5 : if (pid != 0)
3507 : : {
3508 : : /*
3509 : : * Kill the pid if it's still here. If not, that's what we
3510 : : * wanted so ignore any errors.
3511 : : */
42 heikki.linnakangas@i 3512 :GNC 5 : (void) SendProcSignal(pid, sigmode, vxid.procNumber);
3513 : : }
5230 simon@2ndQuadrant.co 3514 :GBC 5 : break;
3515 : : }
3516 : : }
3517 : :
3518 : 5 : LWLockRelease(ProcArrayLock);
3519 : :
3520 : 5 : return pid;
3521 : : }
3522 : :
3523 : : /*
3524 : : * MinimumActiveBackends --- count backends (other than myself) that are
3525 : : * in active transactions. Return true if the count exceeds the
3526 : : * minimum threshold passed. This is used as a heuristic to decide if
3527 : : * a pre-XLOG-flush delay is worthwhile during commit.
3528 : : *
3529 : : * Do not count backends that are blocked waiting for locks, since they are
3530 : : * not going to get to run until someone else commits.
3531 : : */
3532 : : bool
4876 simon@2ndQuadrant.co 3533 :UBC 0 : MinimumActiveBackends(int min)
3534 : : {
6905 tgl@sss.pgh.pa.us 3535 : 0 : ProcArrayStruct *arrayP = procArray;
3536 : 0 : int count = 0;
3537 : : int index;
3538 : :
3539 : : /* Quick short-circuit if no minimum is specified */
4876 simon@2ndQuadrant.co 3540 [ # # ]: 0 : if (min == 0)
3541 : 0 : return true;
3542 : :
3543 : : /*
3544 : : * Note: for speed, we don't acquire ProcArrayLock. This is a little bit
3545 : : * bogus, but since we are only testing fields for zero or nonzero, it
3546 : : * should be OK. The result is only used for heuristic purposes anyway...
3547 : : */
6905 tgl@sss.pgh.pa.us 3548 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3549 : : {
4326 bruce@momjian.us 3550 : 0 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3551 : 0 : PGPROC *proc = &allProcs[pgprocno];
3552 : :
3553 : : /*
3554 : : * Since we're not holding a lock, need to be prepared to deal with
3555 : : * garbage, as someone could have incremented numProcs but not yet
3556 : : * filled the structure.
3557 : : *
3558 : : * If someone just decremented numProcs, 'proc' could also point to a
3559 : : * PGPROC entry that's no longer in the array. It still points to a
3560 : : * PGPROC struct, though, because freed PGPROC entries just go to the
3561 : : * free list and are recycled. Its contents are nonsense in that case,
3562 : : * but that's acceptable for this function.
3563 : : */
3380 sfrost@snowman.net 3564 [ # # ]: 0 : if (pgprocno == -1)
3565 : 0 : continue; /* do not count deleted entries */
6905 tgl@sss.pgh.pa.us 3566 [ # # ]: 0 : if (proc == MyProc)
3567 : 0 : continue; /* do not count myself */
1339 andres@anarazel.de 3568 [ # # ]: 0 : if (proc->xid == InvalidTransactionId)
4524 rhaas@postgresql.org 3569 : 0 : continue; /* do not count if no XID assigned */
6876 tgl@sss.pgh.pa.us 3570 [ # # ]: 0 : if (proc->pid == 0)
3571 : 0 : continue; /* do not count prepared xacts */
6905 3572 [ # # ]: 0 : if (proc->waitLock != NULL)
3573 : 0 : continue; /* do not count if blocked on a lock */
3574 : 0 : count++;
4876 simon@2ndQuadrant.co 3575 [ # # ]: 0 : if (count >= min)
3576 : 0 : break;
3577 : : }
3578 : :
3579 : 0 : return count >= min;
3580 : : }
3581 : :
3582 : : /*
3583 : : * CountDBBackends --- count backends that are using specified database
3584 : : */
3585 : : int
6832 tgl@sss.pgh.pa.us 3586 :CBC 31 : CountDBBackends(Oid databaseid)
3587 : : {
3588 : 31 : ProcArrayStruct *arrayP = procArray;
3589 : 31 : int count = 0;
3590 : : int index;
3591 : :
3592 : 31 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3593 : :
3594 [ + + ]: 38 : for (index = 0; index < arrayP->numProcs; index++)
3595 : : {
4326 bruce@momjian.us 3596 : 7 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3597 : 7 : PGPROC *proc = &allProcs[pgprocno];
3598 : :
6832 tgl@sss.pgh.pa.us 3599 [ - + ]: 7 : if (proc->pid == 0)
6832 tgl@sss.pgh.pa.us 3600 :UBC 0 : continue; /* do not count prepared xacts */
5106 simon@2ndQuadrant.co 3601 [ + - ]:CBC 7 : if (!OidIsValid(databaseid) ||
3602 [ + + ]: 7 : proc->databaseId == databaseid)
6832 tgl@sss.pgh.pa.us 3603 : 2 : count++;
3604 : : }
3605 : :
3606 : 31 : LWLockRelease(ProcArrayLock);
3607 : :
3608 : 31 : return count;
3609 : : }
3610 : :
3611 : : /*
3612 : : * CountDBConnections --- counts database backends ignoring any background
3613 : : * worker processes
3614 : : */
3615 : : int
2629 andrew@dunslane.net 3616 :UBC 0 : CountDBConnections(Oid databaseid)
3617 : : {
3618 : 0 : ProcArrayStruct *arrayP = procArray;
3619 : 0 : int count = 0;
3620 : : int index;
3621 : :
3622 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3623 : :
3624 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3625 : : {
3626 : 0 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3627 : 0 : PGPROC *proc = &allProcs[pgprocno];
3628 : :
2629 andrew@dunslane.net 3629 [ # # ]: 0 : if (proc->pid == 0)
3630 : 0 : continue; /* do not count prepared xacts */
3631 [ # # ]: 0 : if (proc->isBackgroundWorker)
3632 : 0 : continue; /* do not count background workers */
3633 [ # # ]: 0 : if (!OidIsValid(databaseid) ||
3634 [ # # ]: 0 : proc->databaseId == databaseid)
3635 : 0 : count++;
3636 : : }
3637 : :
3638 : 0 : LWLockRelease(ProcArrayLock);
3639 : :
3640 : 0 : return count;
3641 : : }
3642 : :
3643 : : /*
3644 : : * CancelDBBackends --- cancel backends that are using specified database
3645 : : */
3646 : : void
5195 simon@2ndQuadrant.co 3647 :CBC 10 : CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conflictPending)
3648 : : {
5208 3649 : 10 : ProcArrayStruct *arrayP = procArray;
3650 : : int index;
3651 : :
3652 : : /* tell all backends to die */
3653 : 10 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3654 : :
3655 [ + + ]: 20 : for (index = 0; index < arrayP->numProcs; index++)
3656 : : {
4326 bruce@momjian.us 3657 : 10 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3658 : 10 : PGPROC *proc = &allProcs[pgprocno];
3659 : :
5195 simon@2ndQuadrant.co 3660 [ + + + - ]: 10 : if (databaseid == InvalidOid || proc->databaseId == databaseid)
3661 : : {
3662 : : VirtualTransactionId procvxid;
3663 : : pid_t pid;
3664 : :
5202 3665 : 10 : GET_VXID_FROM_PGPROC(procvxid, *proc);
3666 : :
5195 3667 : 10 : proc->recoveryConflictPending = conflictPending;
5202 3668 : 10 : pid = proc->pid;
3669 [ + - ]: 10 : if (pid != 0)
3670 : : {
3671 : : /*
3672 : : * Kill the pid if it's still here. If not, that's what we
3673 : : * wanted so ignore any errors.
3674 : : */
42 heikki.linnakangas@i 3675 :GNC 10 : (void) SendProcSignal(pid, sigmode, procvxid.procNumber);
3676 : : }
3677 : : }
3678 : : }
3679 : :
5208 simon@2ndQuadrant.co 3680 :CBC 10 : LWLockRelease(ProcArrayLock);
3681 : 10 : }
3682 : :
3683 : : /*
3684 : : * CountUserBackends --- count backends that are used by specified user
3685 : : */
3686 : : int
6832 tgl@sss.pgh.pa.us 3687 :UBC 0 : CountUserBackends(Oid roleid)
3688 : : {
3689 : 0 : ProcArrayStruct *arrayP = procArray;
3690 : 0 : int count = 0;
3691 : : int index;
3692 : :
3693 : 0 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3694 : :
3695 [ # # ]: 0 : for (index = 0; index < arrayP->numProcs; index++)
3696 : : {
4326 bruce@momjian.us 3697 : 0 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3698 : 0 : PGPROC *proc = &allProcs[pgprocno];
3699 : :
6832 tgl@sss.pgh.pa.us 3700 [ # # ]: 0 : if (proc->pid == 0)
3701 : 0 : continue; /* do not count prepared xacts */
2629 andrew@dunslane.net 3702 [ # # ]: 0 : if (proc->isBackgroundWorker)
3703 : 0 : continue; /* do not count background workers */
6832 tgl@sss.pgh.pa.us 3704 [ # # ]: 0 : if (proc->roleId == roleid)
3705 : 0 : count++;
3706 : : }
3707 : :
3708 : 0 : LWLockRelease(ProcArrayLock);
3709 : :
3710 : 0 : return count;
3711 : : }
3712 : :
3713 : : /*
3714 : : * CountOtherDBBackends -- check for other backends running in the given DB
3715 : : *
3716 : : * If there are other backends in the DB, we will wait a maximum of 5 seconds
3717 : : * for them to exit. Autovacuum backends are encouraged to exit early by
3718 : : * sending them SIGTERM, but normal user backends are just waited for.
3719 : : *
3720 : : * The current backend is always ignored; it is caller's responsibility to
3721 : : * check whether the current backend uses the given DB, if it's important.
3722 : : *
3723 : : * Returns true if there are (still) other backends in the DB, false if not.
3724 : : * Also, *nbackends and *nprepared are set to the number of other backends
3725 : : * and prepared transactions in the DB, respectively.
3726 : : *
3727 : : * This function is used to interlock DROP DATABASE and related commands
3728 : : * against there being any active backends in the target DB --- dropping the
3729 : : * DB while active backends remain would be a Bad Thing. Note that we cannot
3730 : : * detect here the possibility of a newly-started backend that is trying to
3731 : : * connect to the doomed database, so additional interlocking is needed during
3732 : : * backend startup. The caller should normally hold an exclusive lock on the
3733 : : * target DB before calling this, which is one reason we mustn't wait
3734 : : * indefinitely.
3735 : : */
3736 : : bool
5732 tgl@sss.pgh.pa.us 3737 :CBC 335 : CountOtherDBBackends(Oid databaseId, int *nbackends, int *nprepared)
3738 : : {
6162 3739 : 335 : ProcArrayStruct *arrayP = procArray;
3740 : :
3741 : : #define MAXAUTOVACPIDS 10 /* max autovacs to SIGTERM per iteration */
3742 : : int autovac_pids[MAXAUTOVACPIDS];
3743 : : int tries;
3744 : :
3745 : : /* 50 tries with 100ms sleep between tries makes 5 sec total wait */
3746 [ + - ]: 335 : for (tries = 0; tries < 50; tries++)
3747 : : {
5732 3748 : 335 : int nautovacs = 0;
6162 3749 : 335 : bool found = false;
3750 : : int index;
3751 : :
3752 [ - + ]: 335 : CHECK_FOR_INTERRUPTS();
3753 : :
5732 3754 : 335 : *nbackends = *nprepared = 0;
3755 : :
6162 3756 : 335 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3757 : :
3758 [ + + ]: 1197 : for (index = 0; index < arrayP->numProcs; index++)
3759 : : {
4326 bruce@momjian.us 3760 : 862 : int pgprocno = arrayP->pgprocnos[index];
1983 andres@anarazel.de 3761 : 862 : PGPROC *proc = &allProcs[pgprocno];
1245 alvherre@alvh.no-ip. 3762 : 862 : uint8 statusFlags = ProcGlobal->statusFlags[index];
3763 : :
6162 tgl@sss.pgh.pa.us 3764 [ + + ]: 862 : if (proc->databaseId != databaseId)
3765 : 788 : continue;
3766 [ + - ]: 74 : if (proc == MyProc)
3767 : 74 : continue;
3768 : :
6162 tgl@sss.pgh.pa.us 3769 :UBC 0 : found = true;
3770 : :
5732 3771 [ # # ]: 0 : if (proc->pid == 0)
3772 : 0 : (*nprepared)++;
3773 : : else
3774 : : {
3775 : 0 : (*nbackends)++;
1245 alvherre@alvh.no-ip. 3776 [ # # # # ]: 0 : if ((statusFlags & PROC_IS_AUTOVACUUM) &&
3777 : : nautovacs < MAXAUTOVACPIDS)
5732 tgl@sss.pgh.pa.us 3778 : 0 : autovac_pids[nautovacs++] = proc->pid;
3779 : : }
3780 : : }
3781 : :
5732 tgl@sss.pgh.pa.us 3782 :CBC 335 : LWLockRelease(ProcArrayLock);
3783 : :
6162 3784 [ + - ]: 335 : if (!found)
5995 bruce@momjian.us 3785 : 335 : return false; /* no conflicting backends, so done */
3786 : :
3787 : : /*
3788 : : * Send SIGTERM to any conflicting autovacuums before sleeping. We
3789 : : * postpone this step until after the loop because we don't want to
3790 : : * hold ProcArrayLock while issuing kill(). We have no idea what might
3791 : : * block kill() inside the kernel...
3792 : : */
5732 tgl@sss.pgh.pa.us 3793 [ # # ]:UBC 0 : for (index = 0; index < nautovacs; index++)
3794 : 0 : (void) kill(autovac_pids[index], SIGTERM); /* ignore any error */
3795 : :
3796 : : /* sleep, then try again */
5995 bruce@momjian.us 3797 : 0 : pg_usleep(100 * 1000L); /* 100ms */
3798 : : }
3799 : :
3800 : 0 : return true; /* timed out, still conflicts */
3801 : : }
3802 : :
3803 : : /*
3804 : : * Terminate existing connections to the specified database. This routine
3805 : : * is used by the DROP DATABASE command when user has asked to forcefully
3806 : : * drop the database.
3807 : : *
3808 : : * The current backend is always ignored; it is caller's responsibility to
3809 : : * check whether the current backend uses the given DB, if it's important.
3810 : : *
3811 : : * It doesn't allow to terminate the connections even if there is a one
3812 : : * backend with the prepared transaction in the target database.
3813 : : */
3814 : : void
1615 akapila@postgresql.o 3815 :CBC 1 : TerminateOtherDBBackends(Oid databaseId)
3816 : : {
3817 : 1 : ProcArrayStruct *arrayP = procArray;
3818 : 1 : List *pids = NIL;
3819 : 1 : int nprepared = 0;
3820 : : int i;
3821 : :
3822 : 1 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3823 : :
3824 [ + + ]: 4 : for (i = 0; i < procArray->numProcs; i++)
3825 : : {
3826 : 3 : int pgprocno = arrayP->pgprocnos[i];
3827 : 3 : PGPROC *proc = &allProcs[pgprocno];
3828 : :
3829 [ + - ]: 3 : if (proc->databaseId != databaseId)
3830 : 3 : continue;
1615 akapila@postgresql.o 3831 [ # # ]:UBC 0 : if (proc == MyProc)
3832 : 0 : continue;
3833 : :
3834 [ # # ]: 0 : if (proc->pid != 0)
3835 : 0 : pids = lappend_int(pids, proc->pid);
3836 : : else
3837 : 0 : nprepared++;
3838 : : }
3839 : :
1615 akapila@postgresql.o 3840 :CBC 1 : LWLockRelease(ProcArrayLock);
3841 : :
3842 [ - + ]: 1 : if (nprepared > 0)
1615 akapila@postgresql.o 3843 [ # # ]:UBC 0 : ereport(ERROR,
3844 : : (errcode(ERRCODE_OBJECT_IN_USE),
3845 : : errmsg("database \"%s\" is being used by prepared transactions",
3846 : : get_database_name(databaseId)),
3847 : : errdetail_plural("There is %d prepared transaction using the database.",
3848 : : "There are %d prepared transactions using the database.",
3849 : : nprepared,
3850 : : nprepared)));
3851 : :
1615 akapila@postgresql.o 3852 [ - + ]:CBC 1 : if (pids)
3853 : : {
3854 : : ListCell *lc;
3855 : :
3856 : : /*
3857 : : * Check whether we have the necessary rights to terminate other
3858 : : * sessions. We don't terminate any session until we ensure that we
3859 : : * have rights on all the sessions to be terminated. These checks are
3860 : : * the same as we do in pg_terminate_backend.
3861 : : *
3862 : : * In this case we don't raise some warnings - like "PID %d is not a
3863 : : * PostgreSQL server process", because for us already finished session
3864 : : * is not a problem.
3865 : : */
1615 akapila@postgresql.o 3866 [ # # # # :UBC 0 : foreach(lc, pids)
# # ]
3867 : : {
3868 : 0 : int pid = lfirst_int(lc);
3869 : 0 : PGPROC *proc = BackendPidGetProc(pid);
3870 : :
3871 [ # # ]: 0 : if (proc != NULL)
3872 : : {
3873 : : /* Only allow superusers to signal superuser-owned backends. */
3874 [ # # # # ]: 0 : if (superuser_arg(proc->roleId) && !superuser())
3875 [ # # ]: 0 : ereport(ERROR,
3876 : : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
3877 : : errmsg("permission denied to terminate process"),
3878 : : errdetail("Only roles with the %s attribute may terminate processes of roles with the %s attribute.",
3879 : : "SUPERUSER", "SUPERUSER")));
3880 : :
3881 : : /* Users can signal backends they have role membership in. */
3882 [ # # ]: 0 : if (!has_privs_of_role(GetUserId(), proc->roleId) &&
1109 sfrost@snowman.net 3883 [ # # ]: 0 : !has_privs_of_role(GetUserId(), ROLE_PG_SIGNAL_BACKEND))
1615 akapila@postgresql.o 3884 [ # # ]: 0 : ereport(ERROR,
3885 : : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
3886 : : errmsg("permission denied to terminate process"),
3887 : : errdetail("Only roles with privileges of the role whose process is being terminated or with privileges of the \"%s\" role may terminate this process.",
3888 : : "pg_signal_backend")));
3889 : : }
3890 : : }
3891 : :
3892 : : /*
3893 : : * There's a race condition here: once we release the ProcArrayLock,
3894 : : * it's possible for the session to exit before we issue kill. That
3895 : : * race condition possibility seems too unlikely to worry about. See
3896 : : * pg_signal_backend.
3897 : : */
3898 [ # # # # : 0 : foreach(lc, pids)
# # ]
3899 : : {
3900 : 0 : int pid = lfirst_int(lc);
3901 : 0 : PGPROC *proc = BackendPidGetProc(pid);
3902 : :
3903 [ # # ]: 0 : if (proc != NULL)
3904 : : {
3905 : : /*
3906 : : * If we have setsid(), signal the backend's whole process
3907 : : * group
3908 : : */
3909 : : #ifdef HAVE_SETSID
3910 : 0 : (void) kill(-pid, SIGTERM);
3911 : : #else
3912 : : (void) kill(pid, SIGTERM);
3913 : : #endif
3914 : : }
3915 : : }
3916 : : }
1615 akapila@postgresql.o 3917 :CBC 1 : }
3918 : :
3919 : : /*
3920 : : * ProcArraySetReplicationSlotXmin
3921 : : *
3922 : : * Install limits to future computations of the xmin horizon to prevent vacuum
3923 : : * and HOT pruning from removing affected rows still needed by clients with
3924 : : * replication slots.
3925 : : */
3926 : : void
3695 rhaas@postgresql.org 3927 : 2028 : ProcArraySetReplicationSlotXmin(TransactionId xmin, TransactionId catalog_xmin,
3928 : : bool already_locked)
3929 : : {
3930 [ + + - + ]: 2028 : Assert(!already_locked || LWLockHeldByMe(ProcArrayLock));
3931 : :
3932 [ + + ]: 2028 : if (!already_locked)
3933 : 1628 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3934 : :
3726 3935 : 2028 : procArray->replication_slot_xmin = xmin;
3695 3936 : 2028 : procArray->replication_slot_catalog_xmin = catalog_xmin;
3937 : :
3938 [ + + ]: 2028 : if (!already_locked)
3939 : 1628 : LWLockRelease(ProcArrayLock);
3940 : :
509 alvherre@alvh.no-ip. 3941 [ + + ]: 2028 : elog(DEBUG1, "xmin required by slots: data %u, catalog %u",
3942 : : xmin, catalog_xmin);
3695 rhaas@postgresql.org 3943 : 2028 : }
3944 : :
3945 : : /*
3946 : : * ProcArrayGetReplicationSlotXmin
3947 : : *
3948 : : * Return the current slot xmin limits. That's useful to be able to remove
3949 : : * data that's older than those limits.
3950 : : */
3951 : : void
3952 : 22 : ProcArrayGetReplicationSlotXmin(TransactionId *xmin,
3953 : : TransactionId *catalog_xmin)
3954 : : {
3955 : 22 : LWLockAcquire(ProcArrayLock, LW_SHARED);
3956 : :
3957 [ - + ]: 22 : if (xmin != NULL)
3695 rhaas@postgresql.org 3958 :UBC 0 : *xmin = procArray->replication_slot_xmin;
3959 : :
3695 rhaas@postgresql.org 3960 [ + - ]:CBC 22 : if (catalog_xmin != NULL)
3961 : 22 : *catalog_xmin = procArray->replication_slot_catalog_xmin;
3962 : :
3726 3963 : 22 : LWLockRelease(ProcArrayLock);
3964 : 22 : }
3965 : :
3966 : : /*
3967 : : * XidCacheRemoveRunningXids
3968 : : *
3969 : : * Remove a bunch of TransactionIds from the list of known-running
3970 : : * subtransactions for my backend. Both the specified xid and those in
3971 : : * the xids[] array (of length nxids) are removed from the subxids cache.
3972 : : * latestXid must be the latest XID among the group.
3973 : : */
3974 : : void
6063 tgl@sss.pgh.pa.us 3975 : 648 : XidCacheRemoveRunningXids(TransactionId xid,
3976 : : int nxids, const TransactionId *xids,
3977 : : TransactionId latestXid)
3978 : : {
3979 : : int i,
3980 : : j;
3981 : : XidCacheStatus *mysubxidstat;
3982 : :
6433 3983 [ - + ]: 648 : Assert(TransactionIdIsValid(xid));
3984 : :
3985 : : /*
3986 : : * We must hold ProcArrayLock exclusively in order to remove transactions
3987 : : * from the PGPROC array. (See src/backend/access/transam/README.) It's
3988 : : * possible this could be relaxed since we know this routine is only used
3989 : : * to abort subtransactions, but pending closer analysis we'd best be
3990 : : * conservative.
3991 : : *
3992 : : * Note that we do not have to be careful about memory ordering of our own
3993 : : * reads wrt. GetNewTransactionId() here - only this process can modify
3994 : : * relevant fields of MyProc/ProcGlobal->xids[]. But we do have to be
3995 : : * careful about our own writes being well ordered.
3996 : : */
6905 3997 : 648 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
3998 : :
1339 andres@anarazel.de 3999 : 648 : mysubxidstat = &ProcGlobal->subxidStates[MyProc->pgxactoff];
4000 : :
4001 : : /*
4002 : : * Under normal circumstances xid and xids[] will be in increasing order,
4003 : : * as will be the entries in subxids. Scan backwards to avoid O(N^2)
4004 : : * behavior when removing a lot of xids.
4005 : : */
6905 tgl@sss.pgh.pa.us 4006 [ + + ]: 678 : for (i = nxids - 1; i >= 0; i--)
4007 : : {
4008 : 30 : TransactionId anxid = xids[i];
4009 : :
1339 andres@anarazel.de 4010 [ + - ]: 30 : for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
4011 : : {
6905 tgl@sss.pgh.pa.us 4012 [ + - ]: 30 : if (TransactionIdEquals(MyProc->subxids.xids[j], anxid))
4013 : : {
1339 andres@anarazel.de 4014 : 30 : MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
4015 : 30 : pg_write_barrier();
4016 : 30 : mysubxidstat->count--;
4017 : 30 : MyProc->subxidStatus.count--;
6905 tgl@sss.pgh.pa.us 4018 : 30 : break;
4019 : : }
4020 : : }
4021 : :
4022 : : /*
4023 : : * Ordinarily we should have found it, unless the cache has
4024 : : * overflowed. However it's also possible for this routine to be
4025 : : * invoked multiple times for the same subtransaction, in case of an
4026 : : * error during AbortSubTransaction. So instead of Assert, emit a
4027 : : * debug warning.
4028 : : */
1339 andres@anarazel.de 4029 [ - + - - ]: 30 : if (j < 0 && !MyProc->subxidStatus.overflowed)
6905 tgl@sss.pgh.pa.us 4030 [ # # ]:UBC 0 : elog(WARNING, "did not find subXID %u in MyProc", anxid);
4031 : : }
4032 : :
1339 andres@anarazel.de 4033 [ + + ]:CBC 712 : for (j = MyProc->subxidStatus.count - 1; j >= 0; j--)
4034 : : {
6905 tgl@sss.pgh.pa.us 4035 [ + + ]: 711 : if (TransactionIdEquals(MyProc->subxids.xids[j], xid))
4036 : : {
1339 andres@anarazel.de 4037 : 647 : MyProc->subxids.xids[j] = MyProc->subxids.xids[MyProc->subxidStatus.count - 1];
4038 : 647 : pg_write_barrier();
4039 : 647 : mysubxidstat->count--;
4040 : 647 : MyProc->subxidStatus.count--;
6905 tgl@sss.pgh.pa.us 4041 : 647 : break;
4042 : : }
4043 : : }
4044 : : /* Ordinarily we should have found it, unless the cache has overflowed */
1339 andres@anarazel.de 4045 [ + + - + ]: 648 : if (j < 0 && !MyProc->subxidStatus.overflowed)
6905 tgl@sss.pgh.pa.us 4046 [ # # ]:UBC 0 : elog(WARNING, "did not find subXID %u in MyProc", xid);
4047 : :
4048 : : /* Also advance global latestCompletedXid while holding the lock */
1342 andres@anarazel.de 4049 :CBC 648 : MaintainLatestCompletedXid(latestXid);
4050 : :
4051 : : /* ... and xactCompletionCount */
128 heikki.linnakangas@i 4052 :GNC 648 : TransamVariables->xactCompletionCount++;
4053 : :
6905 tgl@sss.pgh.pa.us 4054 :CBC 648 : LWLockRelease(ProcArrayLock);
4055 : 648 : }
4056 : :
4057 : : #ifdef XIDCACHE_DEBUG
4058 : :
4059 : : /*
4060 : : * Print stats about effectiveness of XID cache
4061 : : */
4062 : : static void
4063 : : DisplayXidCache(void)
4064 : : {
4065 : : fprintf(stderr,
4066 : : "XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, knownassigned: %ld, nooflo: %ld, slow: %ld\n",
4067 : : xc_by_recent_xmin,
4068 : : xc_by_known_xact,
4069 : : xc_by_my_xact,
4070 : : xc_by_latest_xid,
4071 : : xc_by_main_xid,
4072 : : xc_by_child_xid,
4073 : : xc_by_known_assigned,
4074 : : xc_no_overflow,
4075 : : xc_slow_answer);
4076 : : }
4077 : : #endif /* XIDCACHE_DEBUG */
4078 : :
4079 : : /*
4080 : : * If rel != NULL, return test state appropriate for relation, otherwise
4081 : : * return state usable for all relations. The latter may consider XIDs as
4082 : : * not-yet-visible-to-everyone that a state for a specific relation would
4083 : : * already consider visible-to-everyone.
4084 : : *
4085 : : * This needs to be called while a snapshot is active or registered, otherwise
4086 : : * there are wraparound and other dangers.
4087 : : *
4088 : : * See comment for GlobalVisState for details.
4089 : : */
4090 : : GlobalVisState *
1341 andres@anarazel.de 4091 : 13640603 : GlobalVisTestFor(Relation rel)
4092 : : {
995 4093 : 13640603 : GlobalVisState *state = NULL;
4094 : :
4095 : : /* XXX: we should assert that a snapshot is pushed or registered */
1341 4096 [ - + ]: 13640603 : Assert(RecentXmin);
4097 : :
995 4098 [ + + + + : 13640603 : switch (GlobalVisHorizonKindForRel(rel))
- ]
4099 : : {
4100 : 63639 : case VISHORIZON_SHARED:
4101 : 63639 : state = &GlobalVisSharedRels;
4102 : 63639 : break;
4103 : 2240215 : case VISHORIZON_CATALOG:
4104 : 2240215 : state = &GlobalVisCatalogRels;
4105 : 2240215 : break;
4106 : 11294931 : case VISHORIZON_DATA:
4107 : 11294931 : state = &GlobalVisDataRels;
4108 : 11294931 : break;
4109 : 41818 : case VISHORIZON_TEMP:
4110 : 41818 : state = &GlobalVisTempRels;
4111 : 41818 : break;
4112 : : }
4113 : :
1341 4114 [ + - - + ]: 13640603 : Assert(FullTransactionIdIsValid(state->definitely_needed) &&
4115 : : FullTransactionIdIsValid(state->maybe_needed));
4116 : :
4117 : 13640603 : return state;
4118 : : }
4119 : :
4120 : : /*
4121 : : * Return true if it's worth updating the accurate maybe_needed boundary.
4122 : : *
4123 : : * As it is somewhat expensive to determine xmin horizons, we don't want to
4124 : : * repeatedly do so when there is a low likelihood of it being beneficial.
4125 : : *
4126 : : * The current heuristic is that we update only if RecentXmin has changed
4127 : : * since the last update. If the oldest currently running transaction has not
4128 : : * finished, it is unlikely that recomputing the horizon would be useful.
4129 : : */
4130 : : static bool
4131 : 303326 : GlobalVisTestShouldUpdate(GlobalVisState *state)
4132 : : {
4133 : : /* hasn't been updated yet */
4134 [ + + ]: 303326 : if (!TransactionIdIsValid(ComputeXidHorizonsResultLastXmin))
4135 : 7433 : return true;
4136 : :
4137 : : /*
4138 : : * If the maybe_needed/definitely_needed boundaries are the same, it's
4139 : : * unlikely to be beneficial to refresh boundaries.
4140 : : */
4141 [ - + ]: 295893 : if (FullTransactionIdFollowsOrEquals(state->maybe_needed,
4142 : : state->definitely_needed))
1341 andres@anarazel.de 4143 :LBC (12) : return false;
4144 : :
4145 : : /* does the last snapshot built have a different xmin? */
1341 andres@anarazel.de 4146 :CBC 295893 : return RecentXmin != ComputeXidHorizonsResultLastXmin;
4147 : : }
4148 : :
4149 : : static void
4150 : 157391 : GlobalVisUpdateApply(ComputeXidHorizonsResult *horizons)
4151 : : {
4152 : : GlobalVisSharedRels.maybe_needed =
4153 : 157391 : FullXidRelativeTo(horizons->latest_completed,
4154 : : horizons->shared_oldest_nonremovable);
4155 : : GlobalVisCatalogRels.maybe_needed =
4156 : 157391 : FullXidRelativeTo(horizons->latest_completed,
4157 : : horizons->catalog_oldest_nonremovable);
4158 : : GlobalVisDataRels.maybe_needed =
4159 : 157391 : FullXidRelativeTo(horizons->latest_completed,
4160 : : horizons->data_oldest_nonremovable);
4161 : : GlobalVisTempRels.maybe_needed =
1264 4162 : 157391 : FullXidRelativeTo(horizons->latest_completed,
4163 : : horizons->temp_oldest_nonremovable);
4164 : :
4165 : : /*
4166 : : * In longer running transactions it's possible that transactions we
4167 : : * previously needed to treat as running aren't around anymore. So update
4168 : : * definitely_needed to not be earlier than maybe_needed.
4169 : : */
4170 : : GlobalVisSharedRels.definitely_needed =
1341 4171 : 157391 : FullTransactionIdNewer(GlobalVisSharedRels.maybe_needed,
4172 : : GlobalVisSharedRels.definitely_needed);
4173 : : GlobalVisCatalogRels.definitely_needed =
4174 : 157391 : FullTransactionIdNewer(GlobalVisCatalogRels.maybe_needed,
4175 : : GlobalVisCatalogRels.definitely_needed);
4176 : : GlobalVisDataRels.definitely_needed =
4177 : 157391 : FullTransactionIdNewer(GlobalVisDataRels.maybe_needed,
4178 : : GlobalVisDataRels.definitely_needed);
1264 4179 : 157391 : GlobalVisTempRels.definitely_needed = GlobalVisTempRels.maybe_needed;
4180 : :
1341 4181 : 157391 : ComputeXidHorizonsResultLastXmin = RecentXmin;
4182 : 157391 : }
4183 : :
4184 : : /*
4185 : : * Update boundaries in GlobalVis{Shared,Catalog, Data}Rels
4186 : : * using ComputeXidHorizons().
4187 : : */
4188 : : static void
4189 : 45029 : GlobalVisUpdate(void)
4190 : : {
4191 : : ComputeXidHorizonsResult horizons;
4192 : :
4193 : : /* updates the horizons as a side-effect */
4194 : 45029 : ComputeXidHorizons(&horizons);
4195 : 45029 : }
4196 : :
4197 : : /*
4198 : : * Return true if no snapshot still considers fxid to be running.
4199 : : *
4200 : : * The state passed needs to have been initialized for the relation fxid is
4201 : : * from (NULL is also OK), otherwise the result may not be correct.
4202 : : *
4203 : : * See comment for GlobalVisState for details.
4204 : : */
4205 : : bool
4206 : 9508599 : GlobalVisTestIsRemovableFullXid(GlobalVisState *state,
4207 : : FullTransactionId fxid)
4208 : : {
4209 : : /*
4210 : : * If fxid is older than maybe_needed bound, it definitely is visible to
4211 : : * everyone.
4212 : : */
4213 [ + + ]: 9508599 : if (FullTransactionIdPrecedes(fxid, state->maybe_needed))
4214 : 2592439 : return true;
4215 : :
4216 : : /*
4217 : : * If fxid is >= definitely_needed bound, it is very likely to still be
4218 : : * considered running.
4219 : : */
4220 [ + + ]: 6916160 : if (FullTransactionIdFollowsOrEquals(fxid, state->definitely_needed))
4221 : 6612834 : return false;
4222 : :
4223 : : /*
4224 : : * fxid is between maybe_needed and definitely_needed, i.e. there might or
4225 : : * might not exist a snapshot considering fxid running. If it makes sense,
4226 : : * update boundaries and recheck.
4227 : : */
4228 [ + + ]: 303326 : if (GlobalVisTestShouldUpdate(state))
4229 : : {
4230 : 45029 : GlobalVisUpdate();
4231 : :
4232 [ - + ]: 45029 : Assert(FullTransactionIdPrecedes(fxid, state->definitely_needed));
4233 : :
4234 : 45029 : return FullTransactionIdPrecedes(fxid, state->maybe_needed);
4235 : : }
4236 : : else
4237 : 258297 : return false;
4238 : : }
4239 : :
4240 : : /*
4241 : : * Wrapper around GlobalVisTestIsRemovableFullXid() for 32bit xids.
4242 : : *
4243 : : * It is crucial that this only gets called for xids from a source that
4244 : : * protects against xid wraparounds (e.g. from a table and thus protected by
4245 : : * relfrozenxid).
4246 : : */
4247 : : bool
4248 : 9507842 : GlobalVisTestIsRemovableXid(GlobalVisState *state, TransactionId xid)
4249 : : {
4250 : : FullTransactionId fxid;
4251 : :
4252 : : /*
4253 : : * Convert 32 bit argument to FullTransactionId. We can do so safely
4254 : : * because we know the xid has to, at the very least, be between
4255 : : * [oldestXid, nextXid), i.e. within 2 billion of xid. To avoid taking a
4256 : : * lock to determine either, we can just compare with
4257 : : * state->definitely_needed, which was based on those value at the time
4258 : : * the current snapshot was built.
4259 : : */
4260 : 9507842 : fxid = FullXidRelativeTo(state->definitely_needed, xid);
4261 : :
4262 : 9507842 : return GlobalVisTestIsRemovableFullXid(state, fxid);
4263 : : }
4264 : :
4265 : : /*
4266 : : * Return FullTransactionId below which all transactions are not considered
4267 : : * running anymore.
4268 : : *
4269 : : * Note: This is less efficient than testing with
4270 : : * GlobalVisTestIsRemovableFullXid as it likely requires building an accurate
4271 : : * cutoff, even in the case all the XIDs compared with the cutoff are outside
4272 : : * [maybe_needed, definitely_needed).
4273 : : */
4274 : : FullTransactionId
1341 andres@anarazel.de 4275 :LBC (18) : GlobalVisTestNonRemovableFullHorizon(GlobalVisState *state)
4276 : : {
4277 : : /* acquire accurate horizon if not already done */
4278 [ # # ]: (18) : if (GlobalVisTestShouldUpdate(state))
4279 : (6) : GlobalVisUpdate();
4280 : :
4281 : (18) : return state->maybe_needed;
4282 : : }
4283 : :
4284 : : /* Convenience wrapper around GlobalVisTestNonRemovableFullHorizon */
4285 : : TransactionId
4286 : (18) : GlobalVisTestNonRemovableHorizon(GlobalVisState *state)
4287 : : {
4288 : : FullTransactionId cutoff;
4289 : :
4290 : (18) : cutoff = GlobalVisTestNonRemovableFullHorizon(state);
4291 : :
4292 : (18) : return XidFromFullTransactionId(cutoff);
4293 : : }
4294 : :
4295 : : /*
4296 : : * Convenience wrapper around GlobalVisTestFor() and
4297 : : * GlobalVisTestIsRemovableFullXid(), see their comments.
4298 : : */
4299 : : bool
1162 pg@bowt.ie 4300 :CBC 757 : GlobalVisCheckRemovableFullXid(Relation rel, FullTransactionId fxid)
4301 : : {
4302 : : GlobalVisState *state;
4303 : :
1341 andres@anarazel.de 4304 : 757 : state = GlobalVisTestFor(rel);
4305 : :
4306 : 757 : return GlobalVisTestIsRemovableFullXid(state, fxid);
4307 : : }
4308 : :
4309 : : /*
4310 : : * Convenience wrapper around GlobalVisTestFor() and
4311 : : * GlobalVisTestIsRemovableXid(), see their comments.
4312 : : */
4313 : : bool
4314 : 6 : GlobalVisCheckRemovableXid(Relation rel, TransactionId xid)
4315 : : {
4316 : : GlobalVisState *state;
4317 : :
4318 : 6 : state = GlobalVisTestFor(rel);
4319 : :
4320 : 6 : return GlobalVisTestIsRemovableXid(state, xid);
4321 : : }
4322 : :
4323 : : /*
4324 : : * Convert a 32 bit transaction id into 64 bit transaction id, by assuming it
4325 : : * is within MaxTransactionId / 2 of XidFromFullTransactionId(rel).
4326 : : *
4327 : : * Be very careful about when to use this function. It can only safely be used
4328 : : * when there is a guarantee that xid is within MaxTransactionId / 2 xids of
4329 : : * rel. That e.g. can be guaranteed if the caller assures a snapshot is
4330 : : * held by the backend and xid is from a table (where vacuum/freezing ensures
4331 : : * the xid has to be within that range), or if xid is from the procarray and
4332 : : * prevents xid wraparound that way.
4333 : : */
4334 : : static inline FullTransactionId
1342 4335 : 11477629 : FullXidRelativeTo(FullTransactionId rel, TransactionId xid)
4336 : : {
4337 : 11477629 : TransactionId rel_xid = XidFromFullTransactionId(rel);
4338 : :
4339 [ - + ]: 11477629 : Assert(TransactionIdIsValid(xid));
4340 [ - + ]: 11477629 : Assert(TransactionIdIsValid(rel_xid));
4341 : :
4342 : : /* not guaranteed to find issues, but likely to catch mistakes */
4343 : 11477629 : AssertTransactionIdInAllowableRange(xid);
4344 : :
4345 : 22955258 : return FullTransactionIdFromU64(U64FromFullTransactionId(rel)
4346 : 11477629 : + (int32) (xid - rel_xid));
4347 : : }
4348 : :
4349 : :
4350 : : /* ----------------------------------------------
4351 : : * KnownAssignedTransactionIds sub-module
4352 : : * ----------------------------------------------
4353 : : */
4354 : :
4355 : : /*
4356 : : * In Hot Standby mode, we maintain a list of transactions that are (or were)
4357 : : * running on the primary at the current point in WAL. These XIDs must be
4358 : : * treated as running by standby transactions, even though they are not in
4359 : : * the standby server's PGPROC array.
4360 : : *
4361 : : * We record all XIDs that we know have been assigned. That includes all the
4362 : : * XIDs seen in WAL records, plus all unobserved XIDs that we can deduce have
4363 : : * been assigned. We can deduce the existence of unobserved XIDs because we
4364 : : * know XIDs are assigned in sequence, with no gaps. The KnownAssignedXids
4365 : : * list expands as new XIDs are observed or inferred, and contracts when
4366 : : * transaction completion records arrive.
4367 : : *
4368 : : * During hot standby we do not fret too much about the distinction between
4369 : : * top-level XIDs and subtransaction XIDs. We store both together in the
4370 : : * KnownAssignedXids list. In backends, this is copied into snapshots in
4371 : : * GetSnapshotData(), taking advantage of the fact that XidInMVCCSnapshot()
4372 : : * doesn't care about the distinction either. Subtransaction XIDs are
4373 : : * effectively treated as top-level XIDs and in the typical case pg_subtrans
4374 : : * links are *not* maintained (which does not affect visibility).
4375 : : *
4376 : : * We have room in KnownAssignedXids and in snapshots to hold maxProcs *
4377 : : * (1 + PGPROC_MAX_CACHED_SUBXIDS) XIDs, so every primary transaction must
4378 : : * report its subtransaction XIDs in a WAL XLOG_XACT_ASSIGNMENT record at
4379 : : * least every PGPROC_MAX_CACHED_SUBXIDS. When we receive one of these
4380 : : * records, we mark the subXIDs as children of the top XID in pg_subtrans,
4381 : : * and then remove them from KnownAssignedXids. This prevents overflow of
4382 : : * KnownAssignedXids and snapshots, at the cost that status checks for these
4383 : : * subXIDs will take a slower path through TransactionIdIsInProgress().
4384 : : * This means that KnownAssignedXids is not necessarily complete for subXIDs,
4385 : : * though it should be complete for top-level XIDs; this is the same situation
4386 : : * that holds with respect to the PGPROC entries in normal running.
4387 : : *
4388 : : * When we throw away subXIDs from KnownAssignedXids, we need to keep track of
4389 : : * that, similarly to tracking overflow of a PGPROC's subxids array. We do
4390 : : * that by remembering the lastOverflowedXid, ie the last thrown-away subXID.
4391 : : * As long as that is within the range of interesting XIDs, we have to assume
4392 : : * that subXIDs are missing from snapshots. (Note that subXID overflow occurs
4393 : : * on primary when 65th subXID arrives, whereas on standby it occurs when 64th
4394 : : * subXID arrives - that is not an error.)
4395 : : *
4396 : : * Should a backend on primary somehow disappear before it can write an abort
4397 : : * record, then we just leave those XIDs in KnownAssignedXids. They actually
4398 : : * aborted but we think they were running; the distinction is irrelevant
4399 : : * because either way any changes done by the transaction are not visible to
4400 : : * backends in the standby. We prune KnownAssignedXids when
4401 : : * XLOG_RUNNING_XACTS arrives, to forestall possible overflow of the
4402 : : * array due to such dead XIDs.
4403 : : */
4404 : :
4405 : : /*
4406 : : * RecordKnownAssignedTransactionIds
4407 : : * Record the given XID in KnownAssignedXids, as well as any preceding
4408 : : * unobserved XIDs.
4409 : : *
4410 : : * RecordKnownAssignedTransactionIds() should be run for *every* WAL record
4411 : : * associated with a transaction. Must be called for each record after we
4412 : : * have executed StartupCLOG() et al, since we must ExtendCLOG() etc..
4413 : : *
4414 : : * Called during recovery in analogy with and in place of GetNewTransactionId()
4415 : : */
4416 : : void
5230 simon@2ndQuadrant.co 4417 : 2703420 : RecordKnownAssignedTransactionIds(TransactionId xid)
4418 : : {
5085 4419 [ - + ]: 2703420 : Assert(standbyState >= STANDBY_INITIALIZED);
5084 4420 [ - + ]: 2703420 : Assert(TransactionIdIsValid(xid));
3796 heikki.linnakangas@i 4421 [ - + ]: 2703420 : Assert(TransactionIdIsValid(latestObservedXid));
4422 : :
125 michael@paquier.xyz 4423 [ - + ]:GNC 2703420 : elog(DEBUG4, "record known xact %u latestObservedXid %u",
4424 : : xid, latestObservedXid);
4425 : :
4426 : : /*
4427 : : * When a newly observed xid arrives, it is frequently the case that it is
4428 : : * *not* the next xid in sequence. When this occurs, we must treat the
4429 : : * intervening xids as running also.
4430 : : */
5230 simon@2ndQuadrant.co 4431 [ + + ]:CBC 2703420 : if (TransactionIdFollows(xid, latestObservedXid))
4432 : : {
4433 : : TransactionId next_expected_xid;
4434 : :
4435 : : /*
4436 : : * Extend subtrans like we do in GetNewTransactionId() during normal
4437 : : * operation using individual extend steps. Note that we do not need
4438 : : * to extend clog since its extensions are WAL logged.
4439 : : *
4440 : : * This part has to be done regardless of standbyState since we
4441 : : * immediately start assigning subtransactions to their toplevel
4442 : : * transactions.
4443 : : */
5100 tgl@sss.pgh.pa.us 4444 : 22384 : next_expected_xid = latestObservedXid;
3796 heikki.linnakangas@i 4445 [ + + ]: 45138 : while (TransactionIdPrecedes(next_expected_xid, xid))
4446 : : {
4447 [ - + ]: 22754 : TransactionIdAdvance(next_expected_xid);
5230 simon@2ndQuadrant.co 4448 : 22754 : ExtendSUBTRANS(next_expected_xid);
4449 : : }
3796 heikki.linnakangas@i 4450 [ - + ]: 22384 : Assert(next_expected_xid == xid);
4451 : :
4452 : : /*
4453 : : * If the KnownAssignedXids machinery isn't up yet, there's nothing
4454 : : * more to do since we don't track assigned xids yet.
4455 : : */
4456 [ - + ]: 22384 : if (standbyState <= STANDBY_INITIALIZED)
4457 : : {
3796 heikki.linnakangas@i 4458 :LBC (3) : latestObservedXid = xid;
4459 : (3) : return;
4460 : : }
4461 : :
4462 : : /*
4463 : : * Add (latestObservedXid, xid] onto the KnownAssignedXids array.
4464 : : */
5100 tgl@sss.pgh.pa.us 4465 :CBC 22384 : next_expected_xid = latestObservedXid;
4466 [ - + ]: 22384 : TransactionIdAdvance(next_expected_xid);
4467 : 22384 : KnownAssignedXidsAdd(next_expected_xid, xid, false);
4468 : :
4469 : : /*
4470 : : * Now we can advance latestObservedXid
4471 : : */
5230 simon@2ndQuadrant.co 4472 : 22384 : latestObservedXid = xid;
4473 : :
4474 : : /* TransamVariables->nextXid must be beyond any observed xid */
1844 tmunro@postgresql.or 4475 : 22384 : AdvanceNextFullTransactionIdPastXid(latestObservedXid);
4476 : : }
4477 : : }
4478 : :
4479 : : /*
4480 : : * ExpireTreeKnownAssignedTransactionIds
4481 : : * Remove the given XIDs from KnownAssignedXids.
4482 : : *
4483 : : * Called during recovery in analogy with and in place of ProcArrayEndTransaction()
4484 : : */
4485 : : void
5230 simon@2ndQuadrant.co 4486 : 20222 : ExpireTreeKnownAssignedTransactionIds(TransactionId xid, int nsubxids,
4487 : : TransactionId *subxids, TransactionId max_xid)
4488 : : {
5085 4489 [ - + ]: 20222 : Assert(standbyState >= STANDBY_INITIALIZED);
4490 : :
4491 : : /*
4492 : : * Uses same locking as transaction commit
4493 : : */
5230 4494 : 20222 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4495 : :
5100 tgl@sss.pgh.pa.us 4496 : 20222 : KnownAssignedXidsRemoveTree(xid, nsubxids, subxids);
4497 : :
4498 : : /* As in ProcArrayEndTransaction, advance latestCompletedXid */
1342 andres@anarazel.de 4499 : 20222 : MaintainLatestCompletedXidRecovery(max_xid);
4500 : :
4501 : : /* ... and xactCompletionCount */
128 heikki.linnakangas@i 4502 :GNC 20222 : TransamVariables->xactCompletionCount++;
4503 : :
5230 simon@2ndQuadrant.co 4504 :CBC 20222 : LWLockRelease(ProcArrayLock);
4505 : 20222 : }
4506 : :
4507 : : /*
4508 : : * ExpireAllKnownAssignedTransactionIds
4509 : : * Remove all entries in KnownAssignedXids and reset lastOverflowedXid.
4510 : : */
4511 : : void
4512 : 94 : ExpireAllKnownAssignedTransactionIds(void)
4513 : : {
4514 : 94 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
5100 tgl@sss.pgh.pa.us 4515 : 94 : KnownAssignedXidsRemovePreceding(InvalidTransactionId);
4516 : :
4517 : : /*
4518 : : * Reset lastOverflowedXid. Currently, lastOverflowedXid has no use after
4519 : : * the call of this function. But do this for unification with what
4520 : : * ExpireOldKnownAssignedTransactionIds() do.
4521 : : */
890 akorotkov@postgresql 4522 : 94 : procArray->lastOverflowedXid = InvalidTransactionId;
5230 simon@2ndQuadrant.co 4523 : 94 : LWLockRelease(ProcArrayLock);
4524 : 94 : }
4525 : :
4526 : : /*
4527 : : * ExpireOldKnownAssignedTransactionIds
4528 : : * Remove KnownAssignedXids entries preceding the given XID and
4529 : : * potentially reset lastOverflowedXid.
4530 : : */
4531 : : void
4532 : 400 : ExpireOldKnownAssignedTransactionIds(TransactionId xid)
4533 : : {
4534 : 400 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4535 : :
4536 : : /*
4537 : : * Reset lastOverflowedXid if we know all transactions that have been
4538 : : * possibly running are being gone. Not doing so could cause an incorrect
4539 : : * lastOverflowedXid value, which makes extra snapshots be marked as
4540 : : * suboverflowed.
4541 : : */
890 akorotkov@postgresql 4542 [ + + ]: 400 : if (TransactionIdPrecedes(procArray->lastOverflowedXid, xid))
4543 : 396 : procArray->lastOverflowedXid = InvalidTransactionId;
5100 tgl@sss.pgh.pa.us 4544 : 400 : KnownAssignedXidsRemovePreceding(xid);
5230 simon@2ndQuadrant.co 4545 : 400 : LWLockRelease(ProcArrayLock);
4546 : 400 : }
4547 : :
4548 : : /*
4549 : : * KnownAssignedTransactionIdsIdleMaintenance
4550 : : * Opportunistically do maintenance work when the startup process
4551 : : * is about to go idle.
4552 : : */
4553 : : void
502 tgl@sss.pgh.pa.us 4554 : 13169 : KnownAssignedTransactionIdsIdleMaintenance(void)
4555 : : {
4556 : 13169 : KnownAssignedXidsCompress(KAX_STARTUP_PROCESS_IDLE, false);
4557 : 13169 : }
4558 : :
4559 : :
4560 : : /*
4561 : : * Private module functions to manipulate KnownAssignedXids
4562 : : *
4563 : : * There are 5 main uses of the KnownAssignedXids data structure:
4564 : : *
4565 : : * * backends taking snapshots - all valid XIDs need to be copied out
4566 : : * * backends seeking to determine presence of a specific XID
4567 : : * * startup process adding new known-assigned XIDs
4568 : : * * startup process removing specific XIDs as transactions end
4569 : : * * startup process pruning array when special WAL records arrive
4570 : : *
4571 : : * This data structure is known to be a hot spot during Hot Standby, so we
4572 : : * go to some lengths to make these operations as efficient and as concurrent
4573 : : * as possible.
4574 : : *
4575 : : * The XIDs are stored in an array in sorted order --- TransactionIdPrecedes
4576 : : * order, to be exact --- to allow binary search for specific XIDs. Note:
4577 : : * in general TransactionIdPrecedes would not provide a total order, but
4578 : : * we know that the entries present at any instant should not extend across
4579 : : * a large enough fraction of XID space to wrap around (the primary would
4580 : : * shut down for fear of XID wrap long before that happens). So it's OK to
4581 : : * use TransactionIdPrecedes as a binary-search comparator.
4582 : : *
4583 : : * It's cheap to maintain the sortedness during insertions, since new known
4584 : : * XIDs are always reported in XID order; we just append them at the right.
4585 : : *
4586 : : * To keep individual deletions cheap, we need to allow gaps in the array.
4587 : : * This is implemented by marking array elements as valid or invalid using
4588 : : * the parallel boolean array KnownAssignedXidsValid[]. A deletion is done
4589 : : * by setting KnownAssignedXidsValid[i] to false, *without* clearing the
4590 : : * XID entry itself. This preserves the property that the XID entries are
4591 : : * sorted, so we can do binary searches easily. Periodically we compress
4592 : : * out the unused entries; that's much cheaper than having to compress the
4593 : : * array immediately on every deletion.
4594 : : *
4595 : : * The actually valid items in KnownAssignedXids[] and KnownAssignedXidsValid[]
4596 : : * are those with indexes tail <= i < head; items outside this subscript range
4597 : : * have unspecified contents. When head reaches the end of the array, we
4598 : : * force compression of unused entries rather than wrapping around, since
4599 : : * allowing wraparound would greatly complicate the search logic. We maintain
4600 : : * an explicit tail pointer so that pruning of old XIDs can be done without
4601 : : * immediately moving the array contents. In most cases only a small fraction
4602 : : * of the array contains valid entries at any instant.
4603 : : *
4604 : : * Although only the startup process can ever change the KnownAssignedXids
4605 : : * data structure, we still need interlocking so that standby backends will
4606 : : * not observe invalid intermediate states. The convention is that backends
4607 : : * must hold shared ProcArrayLock to examine the array. To remove XIDs from
4608 : : * the array, the startup process must hold ProcArrayLock exclusively, for
4609 : : * the usual transactional reasons (compare commit/abort of a transaction
4610 : : * during normal running). Compressing unused entries out of the array
4611 : : * likewise requires exclusive lock. To add XIDs to the array, we just insert
4612 : : * them into slots to the right of the head pointer and then advance the head
4613 : : * pointer. This doesn't require any lock at all, but on machines with weak
4614 : : * memory ordering, we need to be careful that other processors see the array
4615 : : * element changes before they see the head pointer change. We handle this by
4616 : : * using memory barriers when reading or writing the head/tail pointers (unless
4617 : : * the caller holds ProcArrayLock exclusively).
4618 : : *
4619 : : * Algorithmic analysis:
4620 : : *
4621 : : * If we have a maximum of M slots, with N XIDs currently spread across
4622 : : * S elements then we have N <= S <= M always.
4623 : : *
4624 : : * * Adding a new XID is O(1) and needs no lock (unless compression must
4625 : : * happen)
4626 : : * * Compressing the array is O(S) and requires exclusive lock
4627 : : * * Removing an XID is O(logS) and requires exclusive lock
4628 : : * * Taking a snapshot is O(S) and requires shared lock
4629 : : * * Checking for an XID is O(logS) and requires shared lock
4630 : : *
4631 : : * In comparison, using a hash table for KnownAssignedXids would mean that
4632 : : * taking snapshots would be O(M). If we can maintain S << M then the
4633 : : * sorted array technique will deliver significantly faster snapshots.
4634 : : * If we try to keep S too small then we will spend too much time compressing,
4635 : : * so there is an optimal point for any workload mix. We use a heuristic to
4636 : : * decide when to compress the array, though trimming also helps reduce
4637 : : * frequency of compressing. The heuristic requires us to track the number of
4638 : : * currently valid XIDs in the array (N). Except in special cases, we'll
4639 : : * compress when S >= 2N. Bounding S at 2N in turn bounds the time for
4640 : : * taking a snapshot to be O(N), which it would have to be anyway.
4641 : : */
4642 : :
4643 : :
4644 : : /*
4645 : : * Compress KnownAssignedXids by shifting valid data down to the start of the
4646 : : * array, removing any gaps.
4647 : : *
4648 : : * A compression step is forced if "reason" is KAX_NO_SPACE, otherwise
4649 : : * we do it only if a heuristic indicates it's a good time to do it.
4650 : : *
4651 : : * Compression requires holding ProcArrayLock in exclusive mode.
4652 : : * Caller must pass haveLock = true if it already holds the lock.
4653 : : */
4654 : : static void
4655 : 33827 : KnownAssignedXidsCompress(KAXCompressReason reason, bool haveLock)
4656 : : {
1983 andres@anarazel.de 4657 : 33827 : ProcArrayStruct *pArray = procArray;
4658 : : int head,
4659 : : tail,
4660 : : nelements;
4661 : : int compress_index;
4662 : : int i;
4663 : :
4664 : : /* Counters for compression heuristics */
4665 : : static unsigned int transactionEndsCounter;
4666 : : static TimestampTz lastCompressTs;
4667 : :
4668 : : /* Tuning constants */
4669 : : #define KAX_COMPRESS_FREQUENCY 128 /* in transactions */
4670 : : #define KAX_COMPRESS_IDLE_INTERVAL 1000 /* in ms */
4671 : :
4672 : : /*
4673 : : * Since only the startup process modifies the head/tail pointers, we
4674 : : * don't need a lock to read them here.
4675 : : */
5100 tgl@sss.pgh.pa.us 4676 : 33827 : head = pArray->headKnownAssignedXids;
4677 : 33827 : tail = pArray->tailKnownAssignedXids;
502 4678 : 33827 : nelements = head - tail;
4679 : :
4680 : : /*
4681 : : * If we can choose whether to compress, use a heuristic to avoid
4682 : : * compressing too often or not often enough. "Compress" here simply
4683 : : * means moving the values to the beginning of the array, so it is not as
4684 : : * complex or costly as typical data compression algorithms.
4685 : : */
4686 [ + + ]: 33827 : if (nelements == pArray->numKnownAssignedXids)
4687 : : {
4688 : : /*
4689 : : * When there are no gaps between head and tail, don't bother to
4690 : : * compress, except in the KAX_NO_SPACE case where we must compress to
4691 : : * create some space after the head.
4692 : : */
4693 [ + - ]: 16487 : if (reason != KAX_NO_SPACE)
4694 : 16487 : return;
4695 : : }
4696 [ + + ]: 17340 : else if (reason == KAX_TRANSACTION_END)
4697 : : {
4698 : : /*
4699 : : * Consider compressing only once every so many commits. Frequency
4700 : : * determined by benchmarks.
4701 : : */
4702 [ + + ]: 12660 : if ((transactionEndsCounter++) % KAX_COMPRESS_FREQUENCY != 0)
4703 : 12552 : return;
4704 : :
4705 : : /*
4706 : : * Furthermore, compress only if the used part of the array is less
4707 : : * than 50% full (see comments above).
4708 : : */
4709 [ + + ]: 108 : if (nelements < 2 * pArray->numKnownAssignedXids)
5100 4710 : 5 : return;
4711 : : }
502 4712 [ + + ]: 4680 : else if (reason == KAX_STARTUP_PROCESS_IDLE)
4713 : : {
4714 : : /*
4715 : : * We're about to go idle for lack of new WAL, so we might as well
4716 : : * compress. But not too often, to avoid ProcArray lock contention
4717 : : * with readers.
4718 : : */
4719 [ + + ]: 4669 : if (lastCompressTs != 0)
4720 : : {
4721 : : TimestampTz compress_after;
4722 : :
4723 : 4668 : compress_after = TimestampTzPlusMilliseconds(lastCompressTs,
4724 : : KAX_COMPRESS_IDLE_INTERVAL);
4725 [ + + ]: 4668 : if (GetCurrentTimestamp() < compress_after)
4726 : 4628 : return;
4727 : : }
4728 : : }
4729 : :
4730 : : /* Need to compress, so get the lock if we don't have it. */
4731 [ + + ]: 155 : if (!haveLock)
4732 : 41 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
4733 : :
4734 : : /*
4735 : : * We compress the array by reading the valid values from tail to head,
4736 : : * re-aligning data to 0th element.
4737 : : */
5100 4738 : 155 : compress_index = 0;
4739 [ + + ]: 8386 : for (i = tail; i < head; i++)
4740 : : {
4741 [ + + ]: 8231 : if (KnownAssignedXidsValid[i])
4742 : : {
4743 : 483 : KnownAssignedXids[compress_index] = KnownAssignedXids[i];
4744 : 483 : KnownAssignedXidsValid[compress_index] = true;
4745 : 483 : compress_index++;
4746 : : }
4747 : : }
502 4748 [ - + ]: 155 : Assert(compress_index == pArray->numKnownAssignedXids);
4749 : :
5100 4750 : 155 : pArray->tailKnownAssignedXids = 0;
4751 : 155 : pArray->headKnownAssignedXids = compress_index;
4752 : :
502 4753 [ + + ]: 155 : if (!haveLock)
4754 : 41 : LWLockRelease(ProcArrayLock);
4755 : :
4756 : : /* Update timestamp for maintenance. No need to hold lock for this. */
4757 : 155 : lastCompressTs = GetCurrentTimestamp();
4758 : : }
4759 : :
4760 : : /*
4761 : : * Add xids into KnownAssignedXids at the head of the array.
4762 : : *
4763 : : * xids from from_xid to to_xid, inclusive, are added to the array.
4764 : : *
4765 : : * If exclusive_lock is true then caller already holds ProcArrayLock in
4766 : : * exclusive mode, so we need no extra locking here. Else caller holds no
4767 : : * lock, so we need to be sure we maintain sufficient interlocks against
4768 : : * concurrent readers. (Only the startup process ever calls this, so no need
4769 : : * to worry about concurrent writers.)
4770 : : */
4771 : : static void
5100 4772 : 22389 : KnownAssignedXidsAdd(TransactionId from_xid, TransactionId to_xid,
4773 : : bool exclusive_lock)
4774 : : {
1983 andres@anarazel.de 4775 : 22389 : ProcArrayStruct *pArray = procArray;
4776 : : TransactionId next_xid;
4777 : : int head,
4778 : : tail;
4779 : : int nxids;
4780 : : int i;
4781 : :
5100 tgl@sss.pgh.pa.us 4782 [ - + ]: 22389 : Assert(TransactionIdPrecedesOrEquals(from_xid, to_xid));
4783 : :
4784 : : /*
4785 : : * Calculate how many array slots we'll need. Normally this is cheap; in
4786 : : * the unusual case where the XIDs cross the wrap point, we do it the hard
4787 : : * way.
4788 : : */
4789 [ + - ]: 22389 : if (to_xid >= from_xid)
4790 : 22389 : nxids = to_xid - from_xid + 1;
4791 : : else
4792 : : {
5100 tgl@sss.pgh.pa.us 4793 :UBC 0 : nxids = 1;
4794 : 0 : next_xid = from_xid;
4795 [ # # ]: 0 : while (TransactionIdPrecedes(next_xid, to_xid))
4796 : : {
4797 : 0 : nxids++;
4798 [ # # ]: 0 : TransactionIdAdvance(next_xid);
4799 : : }
4800 : : }
4801 : :
4802 : : /*
4803 : : * Since only the startup process modifies the head/tail pointers, we
4804 : : * don't need a lock to read them here.
4805 : : */
5100 tgl@sss.pgh.pa.us 4806 :CBC 22389 : head = pArray->headKnownAssignedXids;
4807 : 22389 : tail = pArray->tailKnownAssignedXids;
4808 : :
4809 [ + - - + ]: 22389 : Assert(head >= 0 && head <= pArray->maxKnownAssignedXids);
4810 [ + - - + ]: 22389 : Assert(tail >= 0 && tail < pArray->maxKnownAssignedXids);
4811 : :
4812 : : /*
4813 : : * Verify that insertions occur in TransactionId sequence. Note that even
4814 : : * if the last existing element is marked invalid, it must still have a
4815 : : * correctly sequenced XID value.
4816 : : */
4817 [ + + - + ]: 37938 : if (head > tail &&
4818 : 15549 : TransactionIdFollowsOrEquals(KnownAssignedXids[head - 1], from_xid))
4819 : : {
5100 tgl@sss.pgh.pa.us 4820 :UBC 0 : KnownAssignedXidsDisplay(LOG);
4821 [ # # ]: 0 : elog(ERROR, "out-of-order XID insertion in KnownAssignedXids");
4822 : : }
4823 : :
4824 : : /*
4825 : : * If our xids won't fit in the remaining space, compress out free space
4826 : : */
5100 tgl@sss.pgh.pa.us 4827 [ - + ]:CBC 22389 : if (head + nxids > pArray->maxKnownAssignedXids)
4828 : : {
502 tgl@sss.pgh.pa.us 4829 :UBC 0 : KnownAssignedXidsCompress(KAX_NO_SPACE, exclusive_lock);
4830 : :
5100 4831 : 0 : head = pArray->headKnownAssignedXids;
4832 : : /* note: we no longer care about the tail pointer */
4833 : :
4834 : : /*
4835 : : * If it still won't fit then we're out of memory
4836 : : */
4837 [ # # ]: 0 : if (head + nxids > pArray->maxKnownAssignedXids)
1471 peter@eisentraut.org 4838 [ # # ]: 0 : elog(ERROR, "too many KnownAssignedXids");
4839 : : }
4840 : :
4841 : : /* Now we can insert the xids into the space starting at head */
5100 tgl@sss.pgh.pa.us 4842 :CBC 22389 : next_xid = from_xid;
4843 [ + + ]: 45148 : for (i = 0; i < nxids; i++)
4844 : : {
4845 : 22759 : KnownAssignedXids[head] = next_xid;
4846 : 22759 : KnownAssignedXidsValid[head] = true;
4847 [ - + ]: 22759 : TransactionIdAdvance(next_xid);
4848 : 22759 : head++;
4849 : : }
4850 : :
4851 : : /* Adjust count of number of valid entries */
4852 : 22389 : pArray->numKnownAssignedXids += nxids;
4853 : :
4854 : : /*
4855 : : * Now update the head pointer. We use a write barrier to ensure that
4856 : : * other processors see the above array updates before they see the head
4857 : : * pointer change. The barrier isn't required if we're holding
4858 : : * ProcArrayLock exclusively.
4859 : : */
222 nathan@postgresql.or 4860 [ + + ]:GNC 22389 : if (!exclusive_lock)
4861 : 22384 : pg_write_barrier();
4862 : :
4863 : 22389 : pArray->headKnownAssignedXids = head;
5100 tgl@sss.pgh.pa.us 4864 :CBC 22389 : }
4865 : :
4866 : : /*
4867 : : * KnownAssignedXidsSearch
4868 : : *
4869 : : * Searches KnownAssignedXids for a specific xid and optionally removes it.
4870 : : * Returns true if it was found, false if not.
4871 : : *
4872 : : * Caller must hold ProcArrayLock in shared or exclusive mode.
4873 : : * Exclusive lock must be held for remove = true.
4874 : : */
4875 : : static bool
4876 : 25053 : KnownAssignedXidsSearch(TransactionId xid, bool remove)
4877 : : {
1983 andres@anarazel.de 4878 : 25053 : ProcArrayStruct *pArray = procArray;
4879 : : int first,
4880 : : last;
4881 : : int head;
4882 : : int tail;
5031 bruce@momjian.us 4883 : 25053 : int result_index = -1;
4884 : :
222 nathan@postgresql.or 4885 :GNC 25053 : tail = pArray->tailKnownAssignedXids;
4886 : 25053 : head = pArray->headKnownAssignedXids;
4887 : :
4888 : : /*
4889 : : * Only the startup process removes entries, so we don't need the read
4890 : : * barrier in that case.
4891 : : */
4892 [ - + ]: 25053 : if (!remove)
222 nathan@postgresql.or 4893 :UNC 0 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
4894 : :
4895 : : /*
4896 : : * Standard binary search. Note we can ignore the KnownAssignedXidsValid
4897 : : * array here, since even invalid entries will contain sorted XIDs.
4898 : : */
5100 tgl@sss.pgh.pa.us 4899 :CBC 25053 : first = tail;
4900 : 25053 : last = head - 1;
4901 [ + + ]: 97154 : while (first <= last)
4902 : : {
4903 : : int mid_index;
4904 : : TransactionId mid_xid;
4905 : :
4906 : 94774 : mid_index = (first + last) / 2;
4907 : 94774 : mid_xid = KnownAssignedXids[mid_index];
4908 : :
4909 [ + + ]: 94774 : if (xid == mid_xid)
4910 : : {
4911 : 22673 : result_index = mid_index;
4912 : 22673 : break;
4913 : : }
4914 [ + + ]: 72101 : else if (TransactionIdPrecedes(xid, mid_xid))
4915 : 18449 : last = mid_index - 1;
4916 : : else
4917 : 53652 : first = mid_index + 1;
4918 : : }
4919 : :
4920 [ + + ]: 25053 : if (result_index < 0)
4921 : 2380 : return false; /* not in array */
4922 : :
4923 [ + + ]: 22673 : if (!KnownAssignedXidsValid[result_index])
4924 : 3 : return false; /* in array, but invalid */
4925 : :
4926 [ + - ]: 22670 : if (remove)
4927 : : {
4928 : 22670 : KnownAssignedXidsValid[result_index] = false;
4929 : :
4930 : 22670 : pArray->numKnownAssignedXids--;
4931 [ - + ]: 22670 : Assert(pArray->numKnownAssignedXids >= 0);
4932 : :
4933 : : /*
4934 : : * If we're removing the tail element then advance tail pointer over
4935 : : * any invalid elements. This will speed future searches.
4936 : : */
4937 [ + + ]: 22670 : if (result_index == tail)
4938 : : {
4939 : 8083 : tail++;
4940 [ + + + + ]: 14922 : while (tail < head && !KnownAssignedXidsValid[tail])
4941 : 6839 : tail++;
4942 [ + + ]: 8083 : if (tail >= head)
4943 : : {
4944 : : /* Array is empty, so we can reset both pointers */
4945 : 6827 : pArray->headKnownAssignedXids = 0;
4946 : 6827 : pArray->tailKnownAssignedXids = 0;
4947 : : }
4948 : : else
4949 : : {
4950 : 1256 : pArray->tailKnownAssignedXids = tail;
4951 : : }
4952 : : }
4953 : : }
4954 : :
4955 : 22670 : return true;
4956 : : }
4957 : :
4958 : : /*
4959 : : * Is the specified XID present in KnownAssignedXids[]?
4960 : : *
4961 : : * Caller must hold ProcArrayLock in shared or exclusive mode.
4962 : : */
4963 : : static bool
5100 tgl@sss.pgh.pa.us 4964 :UBC 0 : KnownAssignedXidExists(TransactionId xid)
4965 : : {
4966 [ # # ]: 0 : Assert(TransactionIdIsValid(xid));
4967 : :
4968 : 0 : return KnownAssignedXidsSearch(xid, false);
4969 : : }
4970 : :
4971 : : /*
4972 : : * Remove the specified XID from KnownAssignedXids[].
4973 : : *
4974 : : * Caller must hold ProcArrayLock in exclusive mode.
4975 : : */
4976 : : static void
5230 simon@2ndQuadrant.co 4977 :CBC 25053 : KnownAssignedXidsRemove(TransactionId xid)
4978 : : {
4979 [ - + ]: 25053 : Assert(TransactionIdIsValid(xid));
4980 : :
125 michael@paquier.xyz 4981 [ - + ]:GNC 25053 : elog(DEBUG4, "remove KnownAssignedXid %u", xid);
4982 : :
4983 : : /*
4984 : : * Note: we cannot consider it an error to remove an XID that's not
4985 : : * present. We intentionally remove subxact IDs while processing
4986 : : * XLOG_XACT_ASSIGNMENT, to avoid array overflow. Then those XIDs will be
4987 : : * removed again when the top-level xact commits or aborts.
4988 : : *
4989 : : * It might be possible to track such XIDs to distinguish this case from
4990 : : * actual errors, but it would be complicated and probably not worth it.
4991 : : * So, just ignore the search result.
4992 : : */
5100 tgl@sss.pgh.pa.us 4993 :CBC 25053 : (void) KnownAssignedXidsSearch(xid, true);
5230 simon@2ndQuadrant.co 4994 : 25053 : }
4995 : :
4996 : : /*
4997 : : * KnownAssignedXidsRemoveTree
4998 : : * Remove xid (if it's not InvalidTransactionId) and all the subxids.
4999 : : *
5000 : : * Caller must hold ProcArrayLock in exclusive mode.
5001 : : */
5002 : : static void
5100 tgl@sss.pgh.pa.us 5003 : 20258 : KnownAssignedXidsRemoveTree(TransactionId xid, int nsubxids,
5004 : : TransactionId *subxids)
5005 : : {
5006 : : int i;
5007 : :
5008 [ + + ]: 20258 : if (TransactionIdIsValid(xid))
5009 : 20222 : KnownAssignedXidsRemove(xid);
5010 : :
5011 [ + + ]: 25089 : for (i = 0; i < nsubxids; i++)
5012 : 4831 : KnownAssignedXidsRemove(subxids[i]);
5013 : :
5014 : : /* Opportunistically compress the array */
502 5015 : 20258 : KnownAssignedXidsCompress(KAX_TRANSACTION_END, true);
5230 simon@2ndQuadrant.co 5016 : 20258 : }
5017 : :
5018 : : /*
5019 : : * Prune KnownAssignedXids up to, but *not* including xid. If xid is invalid
5020 : : * then clear the whole table.
5021 : : *
5022 : : * Caller must hold ProcArrayLock in exclusive mode.
5023 : : */
5024 : : static void
5100 tgl@sss.pgh.pa.us 5025 : 494 : KnownAssignedXidsRemovePreceding(TransactionId removeXid)
5026 : : {
1983 andres@anarazel.de 5027 : 494 : ProcArrayStruct *pArray = procArray;
5031 bruce@momjian.us 5028 : 494 : int count = 0;
5029 : : int head,
5030 : : tail,
5031 : : i;
5032 : :
5100 tgl@sss.pgh.pa.us 5033 [ + + ]: 494 : if (!TransactionIdIsValid(removeXid))
5034 : : {
125 michael@paquier.xyz 5035 [ - + ]:GNC 94 : elog(DEBUG4, "removing all KnownAssignedXids");
5100 tgl@sss.pgh.pa.us 5036 :CBC 94 : pArray->numKnownAssignedXids = 0;
5037 : 94 : pArray->headKnownAssignedXids = pArray->tailKnownAssignedXids = 0;
5038 : 94 : return;
5039 : : }
5040 : :
125 michael@paquier.xyz 5041 [ - + ]:GNC 400 : elog(DEBUG4, "prune KnownAssignedXids to %u", removeXid);
5042 : :
5043 : : /*
5044 : : * Mark entries invalid starting at the tail. Since array is sorted, we
5045 : : * can stop as soon as we reach an entry >= removeXid.
5046 : : */
5100 tgl@sss.pgh.pa.us 5047 :CBC 400 : tail = pArray->tailKnownAssignedXids;
5048 : 400 : head = pArray->headKnownAssignedXids;
5049 : :
5050 [ + + ]: 400 : for (i = tail; i < head; i++)
5051 : : {
5052 [ + - ]: 82 : if (KnownAssignedXidsValid[i])
5053 : : {
5031 bruce@momjian.us 5054 : 82 : TransactionId knownXid = KnownAssignedXids[i];
5055 : :
5100 tgl@sss.pgh.pa.us 5056 [ + - ]: 82 : if (TransactionIdFollowsOrEquals(knownXid, removeXid))
5057 : 82 : break;
5058 : :
5100 tgl@sss.pgh.pa.us 5059 [ # # ]:UBC 0 : if (!StandbyTransactionIdIsPrepared(knownXid))
5060 : : {
5061 : 0 : KnownAssignedXidsValid[i] = false;
5062 : 0 : count++;
5063 : : }
5064 : : }
5065 : : }
5066 : :
5100 tgl@sss.pgh.pa.us 5067 :CBC 400 : pArray->numKnownAssignedXids -= count;
5068 [ - + ]: 400 : Assert(pArray->numKnownAssignedXids >= 0);
5069 : :
5070 : : /*
5071 : : * Advance the tail pointer if we've marked the tail item invalid.
5072 : : */
5073 [ + + ]: 400 : for (i = tail; i < head; i++)
5074 : : {
5075 [ + - ]: 82 : if (KnownAssignedXidsValid[i])
5076 : 82 : break;
5077 : : }
5078 [ + + ]: 400 : if (i >= head)
5079 : : {
5080 : : /* Array is empty, so we can reset both pointers */
5081 : 318 : pArray->headKnownAssignedXids = 0;
5082 : 318 : pArray->tailKnownAssignedXids = 0;
5083 : : }
5084 : : else
5085 : : {
5086 : 82 : pArray->tailKnownAssignedXids = i;
5087 : : }
5088 : :
5089 : : /* Opportunistically compress the array */
502 5090 : 400 : KnownAssignedXidsCompress(KAX_PRUNE, true);
5091 : : }
5092 : :
5093 : : /*
5094 : : * KnownAssignedXidsGet - Get an array of xids by scanning KnownAssignedXids.
5095 : : * We filter out anything >= xmax.
5096 : : *
5097 : : * Returns the number of XIDs stored into xarray[]. Caller is responsible
5098 : : * that array is large enough.
5099 : : *
5100 : : * Caller must hold ProcArrayLock in (at least) shared mode.
5101 : : */
5102 : : static int
5100 tgl@sss.pgh.pa.us 5103 :UBC 0 : KnownAssignedXidsGet(TransactionId *xarray, TransactionId xmax)
5104 : : {
5105 : 0 : TransactionId xtmp = InvalidTransactionId;
5106 : :
5107 : 0 : return KnownAssignedXidsGetAndSetXmin(xarray, &xtmp, xmax);
5108 : : }
5109 : :
5110 : : /*
5111 : : * KnownAssignedXidsGetAndSetXmin - as KnownAssignedXidsGet, plus
5112 : : * we reduce *xmin to the lowest xid value seen if not already lower.
5113 : : *
5114 : : * Caller must hold ProcArrayLock in (at least) shared mode.
5115 : : */
5116 : : static int
5100 tgl@sss.pgh.pa.us 5117 :CBC 1023 : KnownAssignedXidsGetAndSetXmin(TransactionId *xarray, TransactionId *xmin,
5118 : : TransactionId xmax)
5119 : : {
5120 : 1023 : int count = 0;
5121 : : int head,
5122 : : tail;
5123 : : int i;
5124 : :
5125 : : /*
5126 : : * Fetch head just once, since it may change while we loop. We can stop
5127 : : * once we reach the initially seen head, since we are certain that an xid
5128 : : * cannot enter and then leave the array while we hold ProcArrayLock. We
5129 : : * might miss newly-added xids, but they should be >= xmax so irrelevant
5130 : : * anyway.
5131 : : */
3103 rhaas@postgresql.org 5132 : 1023 : tail = procArray->tailKnownAssignedXids;
5133 : 1023 : head = procArray->headKnownAssignedXids;
5134 : :
222 nathan@postgresql.or 5135 :GNC 1023 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
5136 : :
5100 tgl@sss.pgh.pa.us 5137 [ + + ]:CBC 1041 : for (i = tail; i < head; i++)
5138 : : {
5139 : : /* Skip any gaps in the array */
5140 [ + + ]: 80 : if (KnownAssignedXidsValid[i])
5141 : : {
5142 : 74 : TransactionId knownXid = KnownAssignedXids[i];
5143 : :
5144 : : /*
5145 : : * Update xmin if required. Only the first XID need be checked,
5146 : : * since the array is sorted.
5147 : : */
5148 [ + - + + ]: 148 : if (count == 0 &&
5149 : 74 : TransactionIdPrecedes(knownXid, *xmin))
5150 : 12 : *xmin = knownXid;
5151 : :
5152 : : /*
5153 : : * Filter out anything >= xmax, again relying on sorted property
5154 : : * of array.
5155 : : */
5085 simon@2ndQuadrant.co 5156 [ + - + + ]: 148 : if (TransactionIdIsValid(xmax) &&
5157 : 74 : TransactionIdFollowsOrEquals(knownXid, xmax))
5100 tgl@sss.pgh.pa.us 5158 : 62 : break;
5159 : :
5160 : : /* Add knownXid into output array */
5161 : 12 : xarray[count++] = knownXid;
5162 : : }
5163 : : }
5164 : :
5165 : 1023 : return count;
5166 : : }
5167 : :
5168 : : /*
5169 : : * Get oldest XID in the KnownAssignedXids array, or InvalidTransactionId
5170 : : * if nothing there.
5171 : : */
5172 : : static TransactionId
4976 simon@2ndQuadrant.co 5173 : 192 : KnownAssignedXidsGetOldestXmin(void)
5174 : : {
5175 : : int head,
5176 : : tail;
5177 : : int i;
5178 : :
5179 : : /*
5180 : : * Fetch head just once, since it may change while we loop.
5181 : : */
3103 rhaas@postgresql.org 5182 : 192 : tail = procArray->tailKnownAssignedXids;
5183 : 192 : head = procArray->headKnownAssignedXids;
5184 : :
222 nathan@postgresql.or 5185 :GNC 192 : pg_read_barrier(); /* pairs with KnownAssignedXidsAdd */
5186 : :
4976 simon@2ndQuadrant.co 5187 [ + + ]:CBC 192 : for (i = tail; i < head; i++)
5188 : : {
5189 : : /* Skip any gaps in the array */
5190 [ + - ]: 9 : if (KnownAssignedXidsValid[i])
5191 : 9 : return KnownAssignedXids[i];
5192 : : }
5193 : :
5194 : 183 : return InvalidTransactionId;
5195 : : }
5196 : :
5197 : : /*
5198 : : * Display KnownAssignedXids to provide debug trail
5199 : : *
5200 : : * Currently this is only called within startup process, so we need no
5201 : : * special locking.
5202 : : *
5203 : : * Note this is pretty expensive, and much of the expense will be incurred
5204 : : * even if the elog message will get discarded. It's not currently called
5205 : : * in any performance-critical places, however, so no need to be tenser.
5206 : : */
5207 : : static void
5230 5208 : 143 : KnownAssignedXidsDisplay(int trace_level)
5209 : : {
1983 andres@anarazel.de 5210 : 143 : ProcArrayStruct *pArray = procArray;
5211 : : StringInfoData buf;
5212 : : int head,
5213 : : tail,
5214 : : i;
5031 bruce@momjian.us 5215 : 143 : int nxids = 0;
5216 : :
5100 tgl@sss.pgh.pa.us 5217 : 143 : tail = pArray->tailKnownAssignedXids;
5218 : 143 : head = pArray->headKnownAssignedXids;
5219 : :
5230 simon@2ndQuadrant.co 5220 : 143 : initStringInfo(&buf);
5221 : :
5100 tgl@sss.pgh.pa.us 5222 [ + + ]: 153 : for (i = tail; i < head; i++)
5223 : : {
5224 [ + - ]: 10 : if (KnownAssignedXidsValid[i])
5225 : : {
5226 : 10 : nxids++;
4994 rhaas@postgresql.org 5227 : 10 : appendStringInfo(&buf, "[%d]=%u ", i, KnownAssignedXids[i]);
5228 : : }
5229 : : }
5230 : :
5231 [ - + ]: 143 : elog(trace_level, "%d KnownAssignedXids (num=%d tail=%d head=%d) %s",
5232 : : nxids,
5233 : : pArray->numKnownAssignedXids,
5234 : : pArray->tailKnownAssignedXids,
5235 : : pArray->headKnownAssignedXids,
5236 : : buf.data);
5237 : :
5230 simon@2ndQuadrant.co 5238 : 143 : pfree(buf.data);
5239 : 143 : }
5240 : :
5241 : : /*
5242 : : * KnownAssignedXidsReset
5243 : : * Resets KnownAssignedXids to be empty
5244 : : */
5245 : : static void
4328 simon@2ndQuadrant.co 5246 :UBC 0 : KnownAssignedXidsReset(void)
5247 : : {
1983 andres@anarazel.de 5248 : 0 : ProcArrayStruct *pArray = procArray;
5249 : :
4328 simon@2ndQuadrant.co 5250 : 0 : LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
5251 : :
5252 : 0 : pArray->numKnownAssignedXids = 0;
5253 : 0 : pArray->tailKnownAssignedXids = 0;
5254 : 0 : pArray->headKnownAssignedXids = 0;
5255 : :
5256 : 0 : LWLockRelease(ProcArrayLock);
5257 : 0 : }
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