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) 1996-2019, 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 */
34static inline TupleTableSlot *
35ExecScanFetch(ScanState *node,
36 ExecScanAccessMtd accessMtd,
37 ExecScanRecheckMtd recheckMtd)
38{
39 EState *estate = node->ps.state;
40
41 CHECK_FOR_INTERRUPTS();
42
43 if (estate->es_epq_active != NULL)
44 {
45 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 Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
53
54 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 TupleTableSlot *slot = node->ss_ScanTupleSlot;
64
65 if (!(*recheckMtd) (node, slot))
66 ExecClearTuple(slot); /* would not be returned by scan */
67 return slot;
68 }
69 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 TupleTableSlot *slot = node->ss_ScanTupleSlot;
77
78 /* Return empty slot, as we already returned a tuple */
79 return ExecClearTuple(slot);
80 }
81 else if (epqstate->relsubs_slot[scanrelid - 1] != NULL)
82 {
83 /*
84 * Return replacement tuple provided by the EPQ caller.
85 */
86
87 TupleTableSlot *slot = epqstate->relsubs_slot[scanrelid - 1];
88
89 Assert(epqstate->relsubs_rowmark[scanrelid - 1] == NULL);
90
91 /* Mark to remember that we shouldn't return more */
92 epqstate->relsubs_done[scanrelid - 1] = true;
93
94 /* Return empty slot if we haven't got a test tuple */
95 if (TupIsNull(slot))
96 return NULL;
97
98 /* Check if it meets the access-method conditions */
99 if (!(*recheckMtd) (node, slot))
100 return ExecClearTuple(slot); /* would not be returned by
101 * scan */
102 return slot;
103 }
104 else if (epqstate->relsubs_rowmark[scanrelid - 1] != NULL)
105 {
106 /*
107 * Fetch and return replacement tuple using a non-locking rowmark.
108 */
109
110 TupleTableSlot *slot = node->ss_ScanTupleSlot;
111
112 /* Mark to remember that we shouldn't return more */
113 epqstate->relsubs_done[scanrelid - 1] = true;
114
115 if (!EvalPlanQualFetchRowMark(epqstate, scanrelid, slot))
116 return NULL;
117
118 /* Return empty slot if we haven't got a test tuple */
119 if (TupIsNull(slot))
120 return NULL;
121
122 /* Check if it meets the access-method conditions */
123 if (!(*recheckMtd) (node, slot))
124 return ExecClearTuple(slot); /* would not be returned by
125 * scan */
126 return slot;
127 }
128 }
129
130 /*
131 * Run the node-type-specific access method function to get the next tuple
132 */
133 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 in the direction specified
141 * in the global variable ExecDirection.
142 * The access method returns the next tuple and ExecScan() is
143 * responsible for checking the tuple returned against the qual-clause.
144 *
145 * A 'recheck method' must also be provided that can check an
146 * arbitrary tuple of the relation against any qual conditions
147 * that are implemented internal to the access method.
148 *
149 * Conditions:
150 * -- the "cursor" maintained by the AMI is positioned at the tuple
151 * returned previously.
152 *
153 * Initial States:
154 * -- the relation indicated is opened for scanning so that the
155 * "cursor" is positioned before the first qualifying tuple.
156 * ----------------------------------------------------------------
157 */
158TupleTableSlot *
159ExecScan(ScanState *node,
160 ExecScanAccessMtd accessMtd, /* function returning a tuple */
161 ExecScanRecheckMtd recheckMtd)
162{
163 ExprContext *econtext;
164 ExprState *qual;
165 ProjectionInfo *projInfo;
166
167 /*
168 * Fetch data from node
169 */
170 qual = node->ps.qual;
171 projInfo = node->ps.ps_ProjInfo;
172 econtext = node->ps.ps_ExprContext;
173
174 /* interrupt checks are in ExecScanFetch */
175
176 /*
177 * If we have neither a qual to check nor a projection to do, just skip
178 * all the overhead and return the raw scan tuple.
179 */
180 if (!qual && !projInfo)
181 {
182 ResetExprContext(econtext);
183 return ExecScanFetch(node, accessMtd, recheckMtd);
184 }
185
186 /*
187 * Reset per-tuple memory context to free any expression evaluation
188 * storage allocated in the previous tuple cycle.
189 */
190 ResetExprContext(econtext);
191
192 /*
193 * get a tuple from the access method. Loop until we obtain a tuple that
194 * passes the qualification.
195 */
196 for (;;)
197 {
198 TupleTableSlot *slot;
199
200 slot = ExecScanFetch(node, accessMtd, recheckMtd);
201
202 /*
203 * if the slot returned by the accessMtd contains NULL, then it means
204 * there is nothing more to scan so we just return an empty slot,
205 * being careful to use the projection result slot so it has correct
206 * tupleDesc.
207 */
208 if (TupIsNull(slot))
209 {
210 if (projInfo)
211 return ExecClearTuple(projInfo->pi_state.resultslot);
212 else
213 return slot;
214 }
215
216 /*
217 * place the current tuple into the expr context
218 */
219 econtext->ecxt_scantuple = slot;
220
221 /*
222 * check that the current tuple satisfies the qual-clause
223 *
224 * check for non-null qual here to avoid a function call to ExecQual()
225 * when the qual is null ... saves only a few cycles, but they add up
226 * ...
227 */
228 if (qual == NULL || ExecQual(qual, econtext))
229 {
230 /*
231 * Found a satisfactory scan tuple.
232 */
233 if (projInfo)
234 {
235 /*
236 * Form a projection tuple, store it in the result tuple slot
237 * and return it.
238 */
239 return ExecProject(projInfo);
240 }
241 else
242 {
243 /*
244 * Here, we aren't projecting, so just return scan tuple.
245 */
246 return slot;
247 }
248 }
249 else
250 InstrCountFiltered1(node, 1);
251
252 /*
253 * Tuple fails qual, so free per-tuple memory and try again.
254 */
255 ResetExprContext(econtext);
256 }
257}
258
259/*
260 * ExecAssignScanProjectionInfo
261 * Set up projection info for a scan node, if necessary.
262 *
263 * We can avoid a projection step if the requested tlist exactly matches
264 * the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
265 * Note that this case occurs not only for simple "SELECT * FROM ...", but
266 * also in most cases where there are joins or other processing nodes above
267 * the scan node, because the planner will preferentially generate a matching
268 * tlist.
269 *
270 * The scan slot's descriptor must have been set already.
271 */
272void
273ExecAssignScanProjectionInfo(ScanState *node)
274{
275 Scan *scan = (Scan *) node->ps.plan;
276 TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
277
278 ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
279}
280
281/*
282 * ExecAssignScanProjectionInfoWithVarno
283 * As above, but caller can specify varno expected in Vars in the tlist.
284 */
285void
286ExecAssignScanProjectionInfoWithVarno(ScanState *node, Index varno)
287{
288 TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
289
290 ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
291}
292
293/*
294 * ExecScanReScan
295 *
296 * This must be called within the ReScan function of any plan node type
297 * that uses ExecScan().
298 */
299void
300ExecScanReScan(ScanState *node)
301{
302 EState *estate = node->ps.state;
303
304 /*
305 * We must clear the scan tuple so that observers (e.g., execCurrent.c)
306 * can tell that this plan node is not positioned on a tuple.
307 */
308 ExecClearTuple(node->ss_ScanTupleSlot);
309
310 /* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
311 if (estate->es_epq_active != NULL)
312 {
313 EPQState *epqstate = estate->es_epq_active;
314 Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
315
316 if (scanrelid > 0)
317 epqstate->relsubs_done[scanrelid - 1] = false;
318 else
319 {
320 Bitmapset *relids;
321 int rtindex = -1;
322
323 /*
324 * If an FDW or custom scan provider has replaced the join with a
325 * scan, there are multiple RTIs; reset the epqScanDone flag for
326 * all of them.
327 */
328 if (IsA(node->ps.plan, ForeignScan))
329 relids = ((ForeignScan *) node->ps.plan)->fs_relids;
330 else if (IsA(node->ps.plan, CustomScan))
331 relids = ((CustomScan *) node->ps.plan)->custom_relids;
332 else
333 elog(ERROR, "unexpected scan node: %d",
334 (int) nodeTag(node->ps.plan));
335
336 while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
337 {
338 Assert(rtindex > 0);
339 epqstate->relsubs_done[rtindex - 1] = false;
340 }
341 }
342 }
343}
344