1 /*-------------------------------------------------------------------------
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
10 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
11 * Portions Copyright (c) 1994, Regents of the University of California
15 * src/backend/executor/execScan.c
17 *-------------------------------------------------------------------------
21 #include "executor/executor.h"
22 #include "miscadmin.h"
23 #include "utils/memutils.h"
26 static bool tlist_matches_tupdesc(PlanState *ps, List *tlist, Index varno, TupleDesc tupdesc);
30 * ExecScanFetch -- fetch next potential tuple
32 * This routine is concerned with substituting a test tuple if we are
33 * inside an EvalPlanQual recheck. If we aren't, just execute
34 * the access method's next-tuple routine.
36 static inline TupleTableSlot *
37 ExecScanFetch(ScanState *node,
38 ExecScanAccessMtd accessMtd,
39 ExecScanRecheckMtd recheckMtd)
41 EState *estate = node->ps.state;
43 if (estate->es_epqTuple != NULL)
46 * We are inside an EvalPlanQual recheck. Return the test tuple if
47 * one is available, after rechecking any access-method-specific
50 Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
54 TupleTableSlot *slot = node->ss_ScanTupleSlot;
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.
62 if (!(*recheckMtd) (node, slot))
63 ExecClearTuple(slot); /* would not be returned by scan */
66 else if (estate->es_epqTupleSet[scanrelid - 1])
68 TupleTableSlot *slot = node->ss_ScanTupleSlot;
70 /* Return empty slot if we already returned a tuple */
71 if (estate->es_epqScanDone[scanrelid - 1])
72 return ExecClearTuple(slot);
73 /* Else mark to remember that we shouldn't return more */
74 estate->es_epqScanDone[scanrelid - 1] = true;
76 /* Return empty slot if we haven't got a test tuple */
77 if (estate->es_epqTuple[scanrelid - 1] == NULL)
78 return ExecClearTuple(slot);
80 /* Store test tuple in the plan node's scan slot */
81 ExecStoreTuple(estate->es_epqTuple[scanrelid - 1],
82 slot, InvalidBuffer, false);
84 /* Check if it meets the access-method conditions */
85 if (!(*recheckMtd) (node, slot))
86 ExecClearTuple(slot); /* would not be returned by scan */
93 * Run the node-type-specific access method function to get the next tuple
95 return (*accessMtd) (node);
98 /* ----------------------------------------------------------------
101 * Scans the relation using the 'access method' indicated and
102 * returns the next qualifying tuple in the direction specified
103 * in the global variable ExecDirection.
104 * The access method returns the next tuple and ExecScan() is
105 * responsible for checking the tuple returned against the qual-clause.
107 * A 'recheck method' must also be provided that can check an
108 * arbitrary tuple of the relation against any qual conditions
109 * that are implemented internal to the access method.
112 * -- the "cursor" maintained by the AMI is positioned at the tuple
113 * returned previously.
116 * -- the relation indicated is opened for scanning so that the
117 * "cursor" is positioned before the first qualifying tuple.
118 * ----------------------------------------------------------------
121 ExecScan(ScanState *node,
122 ExecScanAccessMtd accessMtd, /* function returning a tuple */
123 ExecScanRecheckMtd recheckMtd)
125 ExprContext *econtext;
127 ProjectionInfo *projInfo;
129 TupleTableSlot *resultSlot;
132 * Fetch data from node
134 qual = node->ps.qual;
135 projInfo = node->ps.ps_ProjInfo;
136 econtext = node->ps.ps_ExprContext;
139 * If we have neither a qual to check nor a projection to do, just skip
140 * all the overhead and return the raw scan tuple.
142 if (!qual && !projInfo)
144 ResetExprContext(econtext);
145 return ExecScanFetch(node, accessMtd, recheckMtd);
149 * Check to see if we're still projecting out tuples from a previous scan
150 * tuple (because there is a function-returning-set in the projection
151 * expressions). If so, try to project another one.
153 if (node->ps.ps_TupFromTlist)
155 Assert(projInfo); /* can't get here if not projecting */
156 resultSlot = ExecProject(projInfo, &isDone);
157 if (isDone == ExprMultipleResult)
159 /* Done with that source tuple... */
160 node->ps.ps_TupFromTlist = false;
164 * Reset per-tuple memory context to free any expression evaluation
165 * storage allocated in the previous tuple cycle. Note this can't happen
166 * until we're done projecting out tuples from a scan tuple.
168 ResetExprContext(econtext);
171 * get a tuple from the access method. Loop until we obtain a tuple that
172 * passes the qualification.
176 TupleTableSlot *slot;
178 CHECK_FOR_INTERRUPTS();
180 slot = ExecScanFetch(node, accessMtd, recheckMtd);
183 * if the slot returned by the accessMtd contains NULL, then it means
184 * there is nothing more to scan so we just return an empty slot,
185 * being careful to use the projection result slot so it has correct
191 return ExecClearTuple(projInfo->pi_slot);
197 * place the current tuple into the expr context
199 econtext->ecxt_scantuple = slot;
202 * check that the current tuple satisfies the qual-clause
204 * check for non-nil qual here to avoid a function call to ExecQual()
205 * when the qual is nil ... saves only a few cycles, but they add up
208 if (!qual || ExecQual(qual, econtext, false))
211 * Found a satisfactory scan tuple.
216 * Form a projection tuple, store it in the result tuple slot
217 * and return it --- unless we find we can project no tuples
218 * from this scan tuple, in which case continue scan.
220 resultSlot = ExecProject(projInfo, &isDone);
221 if (isDone != ExprEndResult)
223 node->ps.ps_TupFromTlist = (isDone == ExprMultipleResult);
230 * Here, we aren't projecting, so just return scan tuple.
236 InstrCountFiltered1(node, 1);
239 * Tuple fails qual, so free per-tuple memory and try again.
241 ResetExprContext(econtext);
246 * ExecAssignScanProjectionInfo
247 * Set up projection info for a scan node, if necessary.
249 * We can avoid a projection step if the requested tlist exactly matches
250 * the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
251 * Note that this case occurs not only for simple "SELECT * FROM ...", but
252 * also in most cases where there are joins or other processing nodes above
253 * the scan node, because the planner will preferentially generate a matching
256 * ExecAssignScanType must have been called already.
259 ExecAssignScanProjectionInfo(ScanState *node)
261 Scan *scan = (Scan *) node->ps.plan;
263 ExecAssignScanProjectionInfoWithVarno(node, scan->scanrelid);
267 * ExecAssignScanProjectionInfoWithVarno
268 * As above, but caller can specify varno expected in Vars in the tlist.
271 ExecAssignScanProjectionInfoWithVarno(ScanState *node, Index varno)
273 Scan *scan = (Scan *) node->ps.plan;
275 if (tlist_matches_tupdesc(&node->ps,
276 scan->plan.targetlist,
278 node->ss_ScanTupleSlot->tts_tupleDescriptor))
279 node->ps.ps_ProjInfo = NULL;
281 ExecAssignProjectionInfo(&node->ps,
282 node->ss_ScanTupleSlot->tts_tupleDescriptor);
286 tlist_matches_tupdesc(PlanState *ps, List *tlist, Index varno, TupleDesc tupdesc)
288 int numattrs = tupdesc->natts;
291 ListCell *tlist_item = list_head(tlist);
293 /* Check the tlist attributes */
294 for (attrno = 1; attrno <= numattrs; attrno++)
296 Form_pg_attribute att_tup = tupdesc->attrs[attrno - 1];
299 if (tlist_item == NULL)
300 return false; /* tlist too short */
301 var = (Var *) ((TargetEntry *) lfirst(tlist_item))->expr;
302 if (!var || !IsA(var, Var))
303 return false; /* tlist item not a Var */
304 /* if these Asserts fail, planner messed up */
305 Assert(var->varno == varno);
306 Assert(var->varlevelsup == 0);
307 if (var->varattno != attrno)
308 return false; /* out of order */
309 if (att_tup->attisdropped)
310 return false; /* table contains dropped columns */
313 * Note: usually the Var's type should match the tupdesc exactly, but
314 * in situations involving unions of columns that have different
315 * typmods, the Var may have come from above the union and hence have
316 * typmod -1. This is a legitimate situation since the Var still
317 * describes the column, just not as exactly as the tupdesc does. We
318 * could change the planner to prevent it, but it'd then insert
319 * projection steps just to convert from specific typmod to typmod -1,
320 * which is pretty silly.
322 if (var->vartype != att_tup->atttypid ||
323 (var->vartypmod != att_tup->atttypmod &&
324 var->vartypmod != -1))
325 return false; /* type mismatch */
327 tlist_item = lnext(tlist_item);
331 return false; /* tlist too long */
334 * If the plan context requires a particular hasoid setting, then that has
337 if (ExecContextForcesOids(ps, &hasoid) &&
338 hasoid != tupdesc->tdhasoid)
347 * This must be called within the ReScan function of any plan node type
348 * that uses ExecScan().
351 ExecScanReScan(ScanState *node)
353 EState *estate = node->ps.state;
355 /* Stop projecting any tuples from SRFs in the targetlist */
356 node->ps.ps_TupFromTlist = false;
358 /* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
359 if (estate->es_epqScanDone != NULL)
361 Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
364 estate->es_epqScanDone[scanrelid - 1] = false;
371 * If an FDW or custom scan provider has replaced the join with a
372 * scan, there are multiple RTIs; reset the epqScanDone flag for
375 if (IsA(node->ps.plan, ForeignScan))
376 relids = ((ForeignScan *) node->ps.plan)->fs_relids;
377 else if (IsA(node->ps.plan, CustomScan))
378 relids = ((CustomScan *) node->ps.plan)->custom_relids;
380 elog(ERROR, "unexpected scan node: %d",
381 (int) nodeTag(node->ps.plan));
383 while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
386 estate->es_epqScanDone[rtindex - 1] = false;