TLA Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * execScan.c
4 : * This code provides support for generalized relation scans. ExecScan
5 : * is passed a node and a pointer to a function to "do the right thing"
6 : * and return a tuple from the relation. ExecScan then does the tedious
7 : * stuff - checking the qualification and projecting the tuple
8 : * appropriately.
9 : *
10 : * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
11 : * Portions Copyright (c) 1994, Regents of the University of California
12 : *
13 : *
14 : * IDENTIFICATION
15 : * src/backend/executor/execScan.c
16 : *
17 : *-------------------------------------------------------------------------
18 : */
19 : #include "postgres.h"
20 :
21 : #include "executor/executor.h"
22 : #include "miscadmin.h"
23 : #include "utils/memutils.h"
24 :
25 :
26 :
27 : /*
28 : * ExecScanFetch -- check interrupts & fetch next potential tuple
29 : *
30 : * This routine is concerned with substituting a test tuple if we are
31 : * inside an EvalPlanQual recheck. If we aren't, just execute
32 : * the access method's next-tuple routine.
33 : */
34 : static inline TupleTableSlot *
35 CBC 53701537 : ExecScanFetch(ScanState *node,
36 : ExecScanAccessMtd accessMtd,
37 : ExecScanRecheckMtd recheckMtd)
38 : {
39 53701537 : EState *estate = node->ps.state;
40 :
41 53701537 : CHECK_FOR_INTERRUPTS();
42 :
43 53701537 : if (estate->es_epq_active != NULL)
44 : {
45 221 : EPQState *epqstate = estate->es_epq_active;
46 :
47 : /*
48 : * We are inside an EvalPlanQual recheck. Return the test tuple if
49 : * one is available, after rechecking any access-method-specific
50 : * conditions.
51 : */
52 221 : Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
53 :
54 221 : if (scanrelid == 0)
55 : {
56 : /*
57 : * This is a ForeignScan or CustomScan which has pushed down a
58 : * join to the remote side. The recheck method is responsible not
59 : * only for rechecking the scan/join quals but also for storing
60 : * the correct tuple in the slot.
61 : */
62 :
63 UBC 0 : TupleTableSlot *slot = node->ss_ScanTupleSlot;
64 :
65 0 : if (!(*recheckMtd) (node, slot))
66 0 : ExecClearTuple(slot); /* would not be returned by scan */
67 0 : return slot;
68 : }
69 CBC 221 : else if (epqstate->relsubs_done[scanrelid - 1])
70 : {
71 : /*
72 : * Return empty slot, as we already performed an EPQ substitution
73 : * for this relation.
74 : */
75 :
76 16 : TupleTableSlot *slot = node->ss_ScanTupleSlot;
77 :
78 : /* Return empty slot, as we already returned a tuple */
79 16 : return ExecClearTuple(slot);
80 : }
81 205 : else if (epqstate->relsubs_slot[scanrelid - 1] != NULL)
82 : {
83 : /*
84 : * Return replacement tuple provided by the EPQ caller.
85 : */
86 :
87 129 : TupleTableSlot *slot = epqstate->relsubs_slot[scanrelid - 1];
88 :
89 129 : Assert(epqstate->relsubs_rowmark[scanrelid - 1] == NULL);
90 :
91 : /* Mark to remember that we shouldn't return more */
92 129 : epqstate->relsubs_done[scanrelid - 1] = true;
93 :
94 : /* Return empty slot if we haven't got a test tuple */
95 129 : if (TupIsNull(slot))
96 15 : return NULL;
97 :
98 : /* Check if it meets the access-method conditions */
99 114 : if (!(*recheckMtd) (node, slot))
100 5 : return ExecClearTuple(slot); /* would not be returned by
101 : * scan */
102 109 : return slot;
103 : }
104 76 : else if (epqstate->relsubs_rowmark[scanrelid - 1] != NULL)
105 : {
106 : /*
107 : * Fetch and return replacement tuple using a non-locking rowmark.
108 : */
109 :
110 7 : TupleTableSlot *slot = node->ss_ScanTupleSlot;
111 :
112 : /* Mark to remember that we shouldn't return more */
113 7 : epqstate->relsubs_done[scanrelid - 1] = true;
114 :
115 7 : if (!EvalPlanQualFetchRowMark(epqstate, scanrelid, slot))
116 UBC 0 : return NULL;
117 :
118 : /* Return empty slot if we haven't got a test tuple */
119 CBC 7 : if (TupIsNull(slot))
120 UBC 0 : return NULL;
121 :
122 : /* Check if it meets the access-method conditions */
123 CBC 7 : if (!(*recheckMtd) (node, slot))
124 UBC 0 : return ExecClearTuple(slot); /* would not be returned by
125 : * scan */
126 CBC 7 : return slot;
127 : }
128 : }
129 :
130 : /*
131 : * Run the node-type-specific access method function to get the next tuple
132 : */
133 53701385 : return (*accessMtd) (node);
134 : }
135 :
136 : /* ----------------------------------------------------------------
137 : * ExecScan
138 : *
139 : * Scans the relation using the 'access method' indicated and
140 : * returns the next qualifying tuple.
141 : * The access method returns the next tuple and ExecScan() is
142 : * responsible for checking the tuple returned against the qual-clause.
143 : *
144 : * A 'recheck method' must also be provided that can check an
145 : * arbitrary tuple of the relation against any qual conditions
146 : * that are implemented internal to the access method.
147 : *
148 : * Conditions:
149 : * -- the "cursor" maintained by the AMI is positioned at the tuple
150 : * returned previously.
151 : *
152 : * Initial States:
153 : * -- the relation indicated is opened for scanning so that the
154 : * "cursor" is positioned before the first qualifying tuple.
155 : * ----------------------------------------------------------------
156 : */
157 : TupleTableSlot *
158 39744821 : ExecScan(ScanState *node,
159 : ExecScanAccessMtd accessMtd, /* function returning a tuple */
160 : ExecScanRecheckMtd recheckMtd)
161 : {
162 : ExprContext *econtext;
163 : ExprState *qual;
164 : ProjectionInfo *projInfo;
165 :
166 : /*
167 : * Fetch data from node
168 : */
169 39744821 : qual = node->ps.qual;
170 39744821 : projInfo = node->ps.ps_ProjInfo;
171 39744821 : econtext = node->ps.ps_ExprContext;
172 :
173 : /* interrupt checks are in ExecScanFetch */
174 :
175 : /*
176 : * If we have neither a qual to check nor a projection to do, just skip
177 : * all the overhead and return the raw scan tuple.
178 : */
179 39744821 : if (!qual && !projInfo)
180 : {
181 13113234 : ResetExprContext(econtext);
182 13113234 : return ExecScanFetch(node, accessMtd, recheckMtd);
183 : }
184 :
185 : /*
186 : * Reset per-tuple memory context to free any expression evaluation
187 : * storage allocated in the previous tuple cycle.
188 : */
189 26631587 : ResetExprContext(econtext);
190 :
191 : /*
192 : * get a tuple from the access method. Loop until we obtain a tuple that
193 : * passes the qualification.
194 : */
195 : for (;;)
196 13956716 : {
197 : TupleTableSlot *slot;
198 :
199 40588303 : slot = ExecScanFetch(node, accessMtd, recheckMtd);
200 :
201 : /*
202 : * if the slot returned by the accessMtd contains NULL, then it means
203 : * there is nothing more to scan so we just return an empty slot,
204 : * being careful to use the projection result slot so it has correct
205 : * tupleDesc.
206 : */
207 40588062 : if (TupIsNull(slot))
208 : {
209 630144 : if (projInfo)
210 582414 : return ExecClearTuple(projInfo->pi_state.resultslot);
211 : else
212 47730 : return slot;
213 : }
214 :
215 : /*
216 : * place the current tuple into the expr context
217 : */
218 39957918 : econtext->ecxt_scantuple = slot;
219 :
220 : /*
221 : * check that the current tuple satisfies the qual-clause
222 : *
223 : * check for non-null qual here to avoid a function call to ExecQual()
224 : * when the qual is null ... saves only a few cycles, but they add up
225 : * ...
226 : */
227 39957918 : if (qual == NULL || ExecQual(qual, econtext))
228 : {
229 : /*
230 : * Found a satisfactory scan tuple.
231 : */
232 26001174 : if (projInfo)
233 : {
234 : /*
235 : * Form a projection tuple, store it in the result tuple slot
236 : * and return it.
237 : */
238 22877743 : return ExecProject(projInfo);
239 : }
240 : else
241 : {
242 : /*
243 : * Here, we aren't projecting, so just return scan tuple.
244 : */
245 3123431 : return slot;
246 : }
247 : }
248 : else
249 13956716 : InstrCountFiltered1(node, 1);
250 :
251 : /*
252 : * Tuple fails qual, so free per-tuple memory and try again.
253 : */
254 13956716 : ResetExprContext(econtext);
255 : }
256 : }
257 :
258 : /*
259 : * ExecAssignScanProjectionInfo
260 : * Set up projection info for a scan node, if necessary.
261 : *
262 : * We can avoid a projection step if the requested tlist exactly matches
263 : * the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
264 : * Note that this case occurs not only for simple "SELECT * FROM ...", but
265 : * also in most cases where there are joins or other processing nodes above
266 : * the scan node, because the planner will preferentially generate a matching
267 : * tlist.
268 : *
269 : * The scan slot's descriptor must have been set already.
270 : */
271 : void
272 202242 : ExecAssignScanProjectionInfo(ScanState *node)
273 : {
274 202242 : Scan *scan = (Scan *) node->ps.plan;
275 202242 : TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
276 :
277 202242 : ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
278 202242 : }
279 :
280 : /*
281 : * ExecAssignScanProjectionInfoWithVarno
282 : * As above, but caller can specify varno expected in Vars in the tlist.
283 : */
284 : void
285 7478 : ExecAssignScanProjectionInfoWithVarno(ScanState *node, int varno)
286 : {
287 7478 : TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
288 :
289 7478 : ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
290 7478 : }
291 :
292 : /*
293 : * ExecScanReScan
294 : *
295 : * This must be called within the ReScan function of any plan node type
296 : * that uses ExecScan().
297 : */
298 : void
299 672543 : ExecScanReScan(ScanState *node)
300 : {
301 672543 : EState *estate = node->ps.state;
302 :
303 : /*
304 : * We must clear the scan tuple so that observers (e.g., execCurrent.c)
305 : * can tell that this plan node is not positioned on a tuple.
306 : */
307 672543 : ExecClearTuple(node->ss_ScanTupleSlot);
308 :
309 : /* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
310 672543 : if (estate->es_epq_active != NULL)
311 : {
312 69 : EPQState *epqstate = estate->es_epq_active;
313 69 : Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
314 :
315 69 : if (scanrelid > 0)
316 69 : epqstate->relsubs_done[scanrelid - 1] = false;
317 : else
318 : {
319 : Bitmapset *relids;
320 UBC 0 : int rtindex = -1;
321 :
322 : /*
323 : * If an FDW or custom scan provider has replaced the join with a
324 : * scan, there are multiple RTIs; reset the epqScanDone flag for
325 : * all of them.
326 : */
327 0 : if (IsA(node->ps.plan, ForeignScan))
328 UNC 0 : relids = ((ForeignScan *) node->ps.plan)->fs_base_relids;
329 UBC 0 : else if (IsA(node->ps.plan, CustomScan))
330 0 : relids = ((CustomScan *) node->ps.plan)->custom_relids;
331 : else
332 0 : elog(ERROR, "unexpected scan node: %d",
333 : (int) nodeTag(node->ps.plan));
334 :
335 0 : while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
336 : {
337 0 : Assert(rtindex > 0);
338 0 : epqstate->relsubs_done[rtindex - 1] = false;
339 : }
340 : }
341 : }
342 CBC 672543 : }
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