Age Owner Branch data TLA Line data Source code
1 : : /*-------------------------------------------------------------------------
2 : : *
3 : : * bufpage.h
4 : : * Standard POSTGRES buffer page definitions.
5 : : *
6 : : *
7 : : * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
8 : : * Portions Copyright (c) 1994, Regents of the University of California
9 : : *
10 : : * src/include/storage/bufpage.h
11 : : *
12 : : *-------------------------------------------------------------------------
13 : : */
14 : : #ifndef BUFPAGE_H
15 : : #define BUFPAGE_H
16 : :
17 : : #include "access/xlogdefs.h"
18 : : #include "storage/block.h"
19 : : #include "storage/item.h"
20 : : #include "storage/off.h"
21 : :
22 : : /*
23 : : * A postgres disk page is an abstraction layered on top of a postgres
24 : : * disk block (which is simply a unit of i/o, see block.h).
25 : : *
26 : : * specifically, while a disk block can be unformatted, a postgres
27 : : * disk page is always a slotted page of the form:
28 : : *
29 : : * +----------------+---------------------------------+
30 : : * | PageHeaderData | linp1 linp2 linp3 ... |
31 : : * +-----------+----+---------------------------------+
32 : : * | ... linpN | |
33 : : * +-----------+--------------------------------------+
34 : : * | ^ pd_lower |
35 : : * | |
36 : : * | v pd_upper |
37 : : * +-------------+------------------------------------+
38 : : * | | tupleN ... |
39 : : * +-------------+------------------+-----------------+
40 : : * | ... tuple3 tuple2 tuple1 | "special space" |
41 : : * +--------------------------------+-----------------+
42 : : * ^ pd_special
43 : : *
44 : : * a page is full when nothing can be added between pd_lower and
45 : : * pd_upper.
46 : : *
47 : : * all blocks written out by an access method must be disk pages.
48 : : *
49 : : * EXCEPTIONS:
50 : : *
51 : : * obviously, a page is not formatted before it is initialized by
52 : : * a call to PageInit.
53 : : *
54 : : * NOTES:
55 : : *
56 : : * linp1..N form an ItemId (line pointer) array. ItemPointers point
57 : : * to a physical block number and a logical offset (line pointer
58 : : * number) within that block/page. Note that OffsetNumbers
59 : : * conventionally start at 1, not 0.
60 : : *
61 : : * tuple1..N are added "backwards" on the page. Since an ItemPointer
62 : : * offset is used to access an ItemId entry rather than an actual
63 : : * byte-offset position, tuples can be physically shuffled on a page
64 : : * whenever the need arises. This indirection also keeps crash recovery
65 : : * relatively simple, because the low-level details of page space
66 : : * management can be controlled by standard buffer page code during
67 : : * logging, and during recovery.
68 : : *
69 : : * AM-generic per-page information is kept in PageHeaderData.
70 : : *
71 : : * AM-specific per-page data (if any) is kept in the area marked "special
72 : : * space"; each AM has an "opaque" structure defined somewhere that is
73 : : * stored as the page trailer. an access method should always
74 : : * initialize its pages with PageInit and then set its own opaque
75 : : * fields.
76 : : */
77 : :
78 : : typedef Pointer Page;
79 : :
80 : :
81 : : /*
82 : : * location (byte offset) within a page.
83 : : *
84 : : * note that this is actually limited to 2^15 because we have limited
85 : : * ItemIdData.lp_off and ItemIdData.lp_len to 15 bits (see itemid.h).
86 : : */
87 : : typedef uint16 LocationIndex;
88 : :
89 : :
90 : : /*
91 : : * For historical reasons, the 64-bit LSN value is stored as two 32-bit
92 : : * values.
93 : : */
94 : : typedef struct
95 : : {
96 : : uint32 xlogid; /* high bits */
97 : : uint32 xrecoff; /* low bits */
98 : : } PageXLogRecPtr;
99 : :
100 : : static inline XLogRecPtr
643 peter@eisentraut.org 101 :CBC 26362815 : PageXLogRecPtrGet(PageXLogRecPtr val)
102 : : {
103 : 26362815 : return (uint64) val.xlogid << 32 | val.xrecoff;
104 : : }
105 : :
106 : : #define PageXLogRecPtrSet(ptr, lsn) \
107 : : ((ptr).xlogid = (uint32) ((lsn) >> 32), (ptr).xrecoff = (uint32) (lsn))
108 : :
109 : : /*
110 : : * disk page organization
111 : : *
112 : : * space management information generic to any page
113 : : *
114 : : * pd_lsn - identifies xlog record for last change to this page.
115 : : * pd_checksum - page checksum, if set.
116 : : * pd_flags - flag bits.
117 : : * pd_lower - offset to start of free space.
118 : : * pd_upper - offset to end of free space.
119 : : * pd_special - offset to start of special space.
120 : : * pd_pagesize_version - size in bytes and page layout version number.
121 : : * pd_prune_xid - oldest XID among potentially prunable tuples on page.
122 : : *
123 : : * The LSN is used by the buffer manager to enforce the basic rule of WAL:
124 : : * "thou shalt write xlog before data". A dirty buffer cannot be dumped
125 : : * to disk until xlog has been flushed at least as far as the page's LSN.
126 : : *
127 : : * pd_checksum stores the page checksum, if it has been set for this page;
128 : : * zero is a valid value for a checksum. If a checksum is not in use then
129 : : * we leave the field unset. This will typically mean the field is zero
130 : : * though non-zero values may also be present if databases have been
131 : : * pg_upgraded from releases prior to 9.3, when the same byte offset was
132 : : * used to store the current timelineid when the page was last updated.
133 : : * Note that there is no indication on a page as to whether the checksum
134 : : * is valid or not, a deliberate design choice which avoids the problem
135 : : * of relying on the page contents to decide whether to verify it. Hence
136 : : * there are no flag bits relating to checksums.
137 : : *
138 : : * pd_prune_xid is a hint field that helps determine whether pruning will be
139 : : * useful. It is currently unused in index pages.
140 : : *
141 : : * The page version number and page size are packed together into a single
142 : : * uint16 field. This is for historical reasons: before PostgreSQL 7.3,
143 : : * there was no concept of a page version number, and doing it this way
144 : : * lets us pretend that pre-7.3 databases have page version number zero.
145 : : * We constrain page sizes to be multiples of 256, leaving the low eight
146 : : * bits available for a version number.
147 : : *
148 : : * Minimum possible page size is perhaps 64B to fit page header, opaque space
149 : : * and a minimal tuple; of course, in reality you want it much bigger, so
150 : : * the constraint on pagesize mod 256 is not an important restriction.
151 : : * On the high end, we can only support pages up to 32KB because lp_off/lp_len
152 : : * are 15 bits.
153 : : */
154 : :
155 : : typedef struct PageHeaderData
156 : : {
157 : : /* XXX LSN is member of *any* block, not only page-organized ones */
158 : : PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog
159 : : * record for last change to this page */
160 : : uint16 pd_checksum; /* checksum */
161 : : uint16 pd_flags; /* flag bits, see below */
162 : : LocationIndex pd_lower; /* offset to start of free space */
163 : : LocationIndex pd_upper; /* offset to end of free space */
164 : : LocationIndex pd_special; /* offset to start of special space */
165 : : uint16 pd_pagesize_version;
166 : : TransactionId pd_prune_xid; /* oldest prunable XID, or zero if none */
167 : : ItemIdData pd_linp[FLEXIBLE_ARRAY_MEMBER]; /* line pointer array */
168 : : } PageHeaderData;
169 : :
170 : : typedef PageHeaderData *PageHeader;
171 : :
172 : : /*
173 : : * pd_flags contains the following flag bits. Undefined bits are initialized
174 : : * to zero and may be used in the future.
175 : : *
176 : : * PD_HAS_FREE_LINES is set if there are any LP_UNUSED line pointers before
177 : : * pd_lower. This should be considered a hint rather than the truth, since
178 : : * changes to it are not WAL-logged.
179 : : *
180 : : * PD_PAGE_FULL is set if an UPDATE doesn't find enough free space in the
181 : : * page for its new tuple version; this suggests that a prune is needed.
182 : : * Again, this is just a hint.
183 : : */
184 : : #define PD_HAS_FREE_LINES 0x0001 /* are there any unused line pointers? */
185 : : #define PD_PAGE_FULL 0x0002 /* not enough free space for new tuple? */
186 : : #define PD_ALL_VISIBLE 0x0004 /* all tuples on page are visible to
187 : : * everyone */
188 : :
189 : : #define PD_VALID_FLAG_BITS 0x0007 /* OR of all valid pd_flags bits */
190 : :
191 : : /*
192 : : * Page layout version number 0 is for pre-7.3 Postgres releases.
193 : : * Releases 7.3 and 7.4 use 1, denoting a new HeapTupleHeader layout.
194 : : * Release 8.0 uses 2; it changed the HeapTupleHeader layout again.
195 : : * Release 8.1 uses 3; it redefined HeapTupleHeader infomask bits.
196 : : * Release 8.3 uses 4; it changed the HeapTupleHeader layout again, and
197 : : * added the pd_flags field (by stealing some bits from pd_tli),
198 : : * as well as adding the pd_prune_xid field (which enlarges the header).
199 : : *
200 : : * As of Release 9.3, the checksum version must also be considered when
201 : : * handling pages.
202 : : */
203 : : #define PG_PAGE_LAYOUT_VERSION 4
204 : : #define PG_DATA_CHECKSUM_VERSION 1
205 : :
206 : : /* ----------------------------------------------------------------
207 : : * page support functions
208 : : * ----------------------------------------------------------------
209 : : */
210 : :
211 : : /*
212 : : * line pointer(s) do not count as part of header
213 : : */
214 : : #define SizeOfPageHeaderData (offsetof(PageHeaderData, pd_linp))
215 : :
216 : : /*
217 : : * PageIsEmpty
218 : : * returns true iff no itemid has been allocated on the page
219 : : */
220 : : static inline bool
221 : 1516777 : PageIsEmpty(Page page)
222 : : {
223 : 1516777 : return ((PageHeader) page)->pd_lower <= SizeOfPageHeaderData;
224 : : }
225 : :
226 : : /*
227 : : * PageIsNew
228 : : * returns true iff page has not been initialized (by PageInit)
229 : : */
230 : : static inline bool
231 : 36676928 : PageIsNew(Page page)
232 : : {
233 : 36676928 : return ((PageHeader) page)->pd_upper == 0;
234 : : }
235 : :
236 : : /*
237 : : * PageGetItemId
238 : : * Returns an item identifier of a page.
239 : : */
240 : : static inline ItemId
241 : 835785919 : PageGetItemId(Page page, OffsetNumber offsetNumber)
242 : : {
243 : 835785919 : return &((PageHeader) page)->pd_linp[offsetNumber - 1];
244 : : }
245 : :
246 : : /*
247 : : * PageGetContents
248 : : * To be used in cases where the page does not contain line pointers.
249 : : *
250 : : * Note: prior to 8.3 this was not guaranteed to yield a MAXALIGN'd result.
251 : : * Now it is. Beware of old code that might think the offset to the contents
252 : : * is just SizeOfPageHeaderData rather than MAXALIGN(SizeOfPageHeaderData).
253 : : */
254 : : static inline char *
255 : 22634450 : PageGetContents(Page page)
256 : : {
257 : 22634450 : return (char *) page + MAXALIGN(SizeOfPageHeaderData);
258 : : }
259 : :
260 : : /* ----------------
261 : : * functions to access page size info
262 : : * ----------------
263 : : */
264 : :
265 : : /*
266 : : * PageGetPageSize
267 : : * Returns the page size of a page.
268 : : *
269 : : * this can only be called on a formatted page (unlike
270 : : * BufferGetPageSize, which can be called on an unformatted page).
271 : : * however, it can be called on a page that is not stored in a buffer.
272 : : */
273 : : static inline Size
274 : 35192737 : PageGetPageSize(Page page)
275 : : {
276 : 35192737 : return (Size) (((PageHeader) page)->pd_pagesize_version & (uint16) 0xFF00);
277 : : }
278 : :
279 : : /*
280 : : * PageGetPageLayoutVersion
281 : : * Returns the page layout version of a page.
282 : : */
283 : : static inline uint8
284 : 3 : PageGetPageLayoutVersion(Page page)
285 : : {
286 : 3 : return (((PageHeader) page)->pd_pagesize_version & 0x00FF);
287 : : }
288 : :
289 : : /*
290 : : * PageSetPageSizeAndVersion
291 : : * Sets the page size and page layout version number of a page.
292 : : *
293 : : * We could support setting these two values separately, but there's
294 : : * no real need for it at the moment.
295 : : */
296 : : static inline void
297 : 317495 : PageSetPageSizeAndVersion(Page page, Size size, uint8 version)
298 : : {
299 [ - + ]: 317495 : Assert((size & 0xFF00) == size);
300 : : Assert((version & 0x00FF) == version);
301 : :
302 : 317495 : ((PageHeader) page)->pd_pagesize_version = size | version;
303 : 317495 : }
304 : :
305 : : /* ----------------
306 : : * page special data functions
307 : : * ----------------
308 : : */
309 : : /*
310 : : * PageGetSpecialSize
311 : : * Returns size of special space on a page.
312 : : */
313 : : static inline uint16
314 : 21323579 : PageGetSpecialSize(Page page)
315 : : {
316 : 21323579 : return (PageGetPageSize(page) - ((PageHeader) page)->pd_special);
317 : : }
318 : :
319 : : /*
320 : : * Using assertions, validate that the page special pointer is OK.
321 : : *
322 : : * This is intended to catch use of the pointer before page initialization.
323 : : */
324 : : static inline void
2927 kgrittn@postgresql.o 325 : 368165263 : PageValidateSpecialPointer(Page page)
326 : : {
643 peter@eisentraut.org 327 [ - + ]: 368165263 : Assert(page);
328 [ - + ]: 368165263 : Assert(((PageHeader) page)->pd_special <= BLCKSZ);
329 [ - + ]: 368165263 : Assert(((PageHeader) page)->pd_special >= SizeOfPageHeaderData);
2927 kgrittn@postgresql.o 330 : 368165263 : }
331 : :
332 : : /*
333 : : * PageGetSpecialPointer
334 : : * Returns pointer to special space on a page.
335 : : */
336 : : static inline char *
643 peter@eisentraut.org 337 : 368165263 : PageGetSpecialPointer(Page page)
338 : : {
339 : 368165263 : PageValidateSpecialPointer(page);
340 : 368165263 : return (char *) page + ((PageHeader) page)->pd_special;
341 : : }
342 : :
343 : : /*
344 : : * PageGetItem
345 : : * Retrieves an item on the given page.
346 : : *
347 : : * Note:
348 : : * This does not change the status of any of the resources passed.
349 : : * The semantics may change in the future.
350 : : */
351 : : static inline Item
352 : 646163614 : PageGetItem(Page page, ItemId itemId)
353 : : {
354 [ - + ]: 646163614 : Assert(page);
355 [ - + ]: 646163614 : Assert(ItemIdHasStorage(itemId));
356 : :
357 : 646163614 : return (Item) (((char *) page) + ItemIdGetOffset(itemId));
358 : : }
359 : :
360 : : /*
361 : : * PageGetMaxOffsetNumber
362 : : * Returns the maximum offset number used by the given page.
363 : : * Since offset numbers are 1-based, this is also the number
364 : : * of items on the page.
365 : : *
366 : : * NOTE: if the page is not initialized (pd_lower == 0), we must
367 : : * return zero to ensure sane behavior.
368 : : */
369 : : static inline OffsetNumber
370 : 243595125 : PageGetMaxOffsetNumber(Page page)
371 : : {
372 : 243595125 : PageHeader pageheader = (PageHeader) page;
373 : :
374 [ + + ]: 243595125 : if (pageheader->pd_lower <= SizeOfPageHeaderData)
375 : 425892 : return 0;
376 : : else
377 : 243169233 : return (pageheader->pd_lower - SizeOfPageHeaderData) / sizeof(ItemIdData);
378 : : }
379 : :
380 : : /*
381 : : * Additional functions for access to page headers.
382 : : */
383 : : static inline XLogRecPtr
384 : 25288743 : PageGetLSN(Page page)
385 : : {
386 : 25288743 : return PageXLogRecPtrGet(((PageHeader) page)->pd_lsn);
387 : : }
388 : : static inline void
389 : 17779170 : PageSetLSN(Page page, XLogRecPtr lsn)
390 : : {
391 : 17779170 : PageXLogRecPtrSet(((PageHeader) page)->pd_lsn, lsn);
392 : 17779170 : }
393 : :
394 : : static inline bool
395 : 11016317 : PageHasFreeLinePointers(Page page)
396 : : {
397 : 11016317 : return ((PageHeader) page)->pd_flags & PD_HAS_FREE_LINES;
398 : : }
399 : : static inline void
400 : 27904 : PageSetHasFreeLinePointers(Page page)
401 : : {
402 : 27904 : ((PageHeader) page)->pd_flags |= PD_HAS_FREE_LINES;
403 : 27904 : }
404 : : static inline void
405 : 60167 : PageClearHasFreeLinePointers(Page page)
406 : : {
407 : 60167 : ((PageHeader) page)->pd_flags &= ~PD_HAS_FREE_LINES;
408 : 60167 : }
409 : :
410 : : static inline bool
411 : 1285097 : PageIsFull(Page page)
412 : : {
413 : 1285097 : return ((PageHeader) page)->pd_flags & PD_PAGE_FULL;
414 : : }
415 : : static inline void
416 : 140150 : PageSetFull(Page page)
417 : : {
418 : 140150 : ((PageHeader) page)->pd_flags |= PD_PAGE_FULL;
419 : 140150 : }
420 : : static inline void
421 : 56458 : PageClearFull(Page page)
422 : : {
423 : 56458 : ((PageHeader) page)->pd_flags &= ~PD_PAGE_FULL;
424 : 56458 : }
425 : :
426 : : static inline bool
427 : 32322474 : PageIsAllVisible(Page page)
428 : : {
429 : 32322474 : return ((PageHeader) page)->pd_flags & PD_ALL_VISIBLE;
430 : : }
431 : : static inline void
432 : 47422 : PageSetAllVisible(Page page)
433 : : {
434 : 47422 : ((PageHeader) page)->pd_flags |= PD_ALL_VISIBLE;
435 : 47422 : }
436 : : static inline void
437 : 25407 : PageClearAllVisible(Page page)
438 : : {
439 : 25407 : ((PageHeader) page)->pd_flags &= ~PD_ALL_VISIBLE;
440 : 25407 : }
441 : :
442 : : /*
443 : : * These two require "access/transam.h", so left as macros.
444 : : */
445 : : #define PageSetPrunable(page, xid) \
446 : : do { \
447 : : Assert(TransactionIdIsNormal(xid)); \
448 : : if (!TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) || \
449 : : TransactionIdPrecedes(xid, ((PageHeader) (page))->pd_prune_xid)) \
450 : : ((PageHeader) (page))->pd_prune_xid = (xid); \
451 : : } while (0)
452 : : #define PageClearPrunable(page) \
453 : : (((PageHeader) (page))->pd_prune_xid = InvalidTransactionId)
454 : :
455 : :
456 : : /* ----------------------------------------------------------------
457 : : * extern declarations
458 : : * ----------------------------------------------------------------
459 : : */
460 : :
461 : : /* flags for PageAddItemExtended() */
462 : : #define PAI_OVERWRITE (1 << 0)
463 : : #define PAI_IS_HEAP (1 << 1)
464 : :
465 : : /* flags for PageIsVerifiedExtended() */
466 : : #define PIV_LOG_WARNING (1 << 0)
467 : : #define PIV_REPORT_STAT (1 << 1)
468 : :
469 : : #define PageAddItem(page, item, size, offsetNumber, overwrite, is_heap) \
470 : : PageAddItemExtended(page, item, size, offsetNumber, \
471 : : ((overwrite) ? PAI_OVERWRITE : 0) | \
472 : : ((is_heap) ? PAI_IS_HEAP : 0))
473 : :
474 : : #define PageIsVerified(page, blkno) \
475 : : PageIsVerifiedExtended(page, blkno, \
476 : : PIV_LOG_WARNING | PIV_REPORT_STAT)
477 : :
478 : : /*
479 : : * Check that BLCKSZ is a multiple of sizeof(size_t). In
480 : : * PageIsVerifiedExtended(), it is much faster to check if a page is
481 : : * full of zeroes using the native word size. Note that this assertion
482 : : * is kept within a header to make sure that StaticAssertDecl() works
483 : : * across various combinations of platforms and compilers.
484 : : */
485 : : StaticAssertDecl(BLCKSZ == ((BLCKSZ / sizeof(size_t)) * sizeof(size_t)),
486 : : "BLCKSZ has to be a multiple of sizeof(size_t)");
487 : :
488 : : extern void PageInit(Page page, Size pageSize, Size specialSize);
489 : : extern bool PageIsVerifiedExtended(Page page, BlockNumber blkno, int flags);
490 : : extern OffsetNumber PageAddItemExtended(Page page, Item item, Size size,
491 : : OffsetNumber offsetNumber, int flags);
492 : : extern Page PageGetTempPage(Page page);
493 : : extern Page PageGetTempPageCopy(Page page);
494 : : extern Page PageGetTempPageCopySpecial(Page page);
495 : : extern void PageRestoreTempPage(Page tempPage, Page oldPage);
496 : : extern void PageRepairFragmentation(Page page);
497 : : extern void PageTruncateLinePointerArray(Page page);
498 : : extern Size PageGetFreeSpace(Page page);
499 : : extern Size PageGetFreeSpaceForMultipleTuples(Page page, int ntups);
500 : : extern Size PageGetExactFreeSpace(Page page);
501 : : extern Size PageGetHeapFreeSpace(Page page);
502 : : extern void PageIndexTupleDelete(Page page, OffsetNumber offnum);
503 : : extern void PageIndexMultiDelete(Page page, OffsetNumber *itemnos, int nitems);
504 : : extern void PageIndexTupleDeleteNoCompact(Page page, OffsetNumber offnum);
505 : : extern bool PageIndexTupleOverwrite(Page page, OffsetNumber offnum,
506 : : Item newtup, Size newsize);
507 : : extern char *PageSetChecksumCopy(Page page, BlockNumber blkno);
508 : : extern void PageSetChecksumInplace(Page page, BlockNumber blkno);
509 : :
510 : : #endif /* BUFPAGE_H */
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