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execScan.c
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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 *
36  ExecScanAccessMtd accessMtd,
37  ExecScanRecheckMtd recheckMtd)
38 {
39  EState *estate = node->ps.state;
40 
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 either there is no EPQ tuple for this rel
73  * or we already returned it.
74  */
75 
76  TupleTableSlot *slot = node->ss_ScanTupleSlot;
77 
78  return ExecClearTuple(slot);
79  }
80  else if (epqstate->relsubs_slot[scanrelid - 1] != NULL)
81  {
82  /*
83  * Return replacement tuple provided by the EPQ caller.
84  */
85 
86  TupleTableSlot *slot = epqstate->relsubs_slot[scanrelid - 1];
87 
88  Assert(epqstate->relsubs_rowmark[scanrelid - 1] == NULL);
89 
90  /* Mark to remember that we shouldn't return it again */
91  epqstate->relsubs_done[scanrelid - 1] = true;
92 
93  /* Return empty slot if we haven't got a test tuple */
94  if (TupIsNull(slot))
95  return NULL;
96 
97  /* Check if it meets the access-method conditions */
98  if (!(*recheckMtd) (node, slot))
99  return ExecClearTuple(slot); /* would not be returned by
100  * scan */
101  return slot;
102  }
103  else if (epqstate->relsubs_rowmark[scanrelid - 1] != NULL)
104  {
105  /*
106  * Fetch and return replacement tuple using a non-locking rowmark.
107  */
108 
109  TupleTableSlot *slot = node->ss_ScanTupleSlot;
110 
111  /* Mark to remember that we shouldn't return more */
112  epqstate->relsubs_done[scanrelid - 1] = true;
113 
114  if (!EvalPlanQualFetchRowMark(epqstate, scanrelid, slot))
115  return NULL;
116 
117  /* Return empty slot if we haven't got a test tuple */
118  if (TupIsNull(slot))
119  return NULL;
120 
121  /* Check if it meets the access-method conditions */
122  if (!(*recheckMtd) (node, slot))
123  return ExecClearTuple(slot); /* would not be returned by
124  * scan */
125  return slot;
126  }
127  }
128 
129  /*
130  * Run the node-type-specific access method function to get the next tuple
131  */
132  return (*accessMtd) (node);
133 }
134 
135 /* ----------------------------------------------------------------
136  * ExecScan
137  *
138  * Scans the relation using the 'access method' indicated and
139  * returns the next qualifying tuple.
140  * The access method returns the next tuple and ExecScan() is
141  * responsible for checking the tuple returned against the qual-clause.
142  *
143  * A 'recheck method' must also be provided that can check an
144  * arbitrary tuple of the relation against any qual conditions
145  * that are implemented internal to the access method.
146  *
147  * Conditions:
148  * -- the "cursor" maintained by the AMI is positioned at the tuple
149  * returned previously.
150  *
151  * Initial States:
152  * -- the relation indicated is opened for scanning so that the
153  * "cursor" is positioned before the first qualifying tuple.
154  * ----------------------------------------------------------------
155  */
158  ExecScanAccessMtd accessMtd, /* function returning a tuple */
159  ExecScanRecheckMtd recheckMtd)
160 {
161  ExprContext *econtext;
162  ExprState *qual;
163  ProjectionInfo *projInfo;
164 
165  /*
166  * Fetch data from node
167  */
168  qual = node->ps.qual;
169  projInfo = node->ps.ps_ProjInfo;
170  econtext = node->ps.ps_ExprContext;
171 
172  /* interrupt checks are in ExecScanFetch */
173 
174  /*
175  * If we have neither a qual to check nor a projection to do, just skip
176  * all the overhead and return the raw scan tuple.
177  */
178  if (!qual && !projInfo)
179  {
180  ResetExprContext(econtext);
181  return ExecScanFetch(node, accessMtd, recheckMtd);
182  }
183 
184  /*
185  * Reset per-tuple memory context to free any expression evaluation
186  * storage allocated in the previous tuple cycle.
187  */
188  ResetExprContext(econtext);
189 
190  /*
191  * get a tuple from the access method. Loop until we obtain a tuple that
192  * passes the qualification.
193  */
194  for (;;)
195  {
196  TupleTableSlot *slot;
197 
198  slot = ExecScanFetch(node, accessMtd, recheckMtd);
199 
200  /*
201  * if the slot returned by the accessMtd contains NULL, then it means
202  * there is nothing more to scan so we just return an empty slot,
203  * being careful to use the projection result slot so it has correct
204  * tupleDesc.
205  */
206  if (TupIsNull(slot))
207  {
208  if (projInfo)
209  return ExecClearTuple(projInfo->pi_state.resultslot);
210  else
211  return slot;
212  }
213 
214  /*
215  * place the current tuple into the expr context
216  */
217  econtext->ecxt_scantuple = slot;
218 
219  /*
220  * check that the current tuple satisfies the qual-clause
221  *
222  * check for non-null qual here to avoid a function call to ExecQual()
223  * when the qual is null ... saves only a few cycles, but they add up
224  * ...
225  */
226  if (qual == NULL || ExecQual(qual, econtext))
227  {
228  /*
229  * Found a satisfactory scan tuple.
230  */
231  if (projInfo)
232  {
233  /*
234  * Form a projection tuple, store it in the result tuple slot
235  * and return it.
236  */
237  return ExecProject(projInfo);
238  }
239  else
240  {
241  /*
242  * Here, we aren't projecting, so just return scan tuple.
243  */
244  return slot;
245  }
246  }
247  else
248  InstrCountFiltered1(node, 1);
249 
250  /*
251  * Tuple fails qual, so free per-tuple memory and try again.
252  */
253  ResetExprContext(econtext);
254  }
255 }
256 
257 /*
258  * ExecAssignScanProjectionInfo
259  * Set up projection info for a scan node, if necessary.
260  *
261  * We can avoid a projection step if the requested tlist exactly matches
262  * the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
263  * Note that this case occurs not only for simple "SELECT * FROM ...", but
264  * also in most cases where there are joins or other processing nodes above
265  * the scan node, because the planner will preferentially generate a matching
266  * tlist.
267  *
268  * The scan slot's descriptor must have been set already.
269  */
270 void
272 {
273  Scan *scan = (Scan *) node->ps.plan;
275 
276  ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
277 }
278 
279 /*
280  * ExecAssignScanProjectionInfoWithVarno
281  * As above, but caller can specify varno expected in Vars in the tlist.
282  */
283 void
285 {
287 
288  ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
289 }
290 
291 /*
292  * ExecScanReScan
293  *
294  * This must be called within the ReScan function of any plan node type
295  * that uses ExecScan().
296  */
297 void
299 {
300  EState *estate = node->ps.state;
301 
302  /*
303  * We must clear the scan tuple so that observers (e.g., execCurrent.c)
304  * can tell that this plan node is not positioned on a tuple.
305  */
307 
308  /*
309  * Rescan EvalPlanQual tuple(s) if we're inside an EvalPlanQual recheck.
310  * But don't lose the "blocked" status of blocked target relations.
311  */
312  if (estate->es_epq_active != NULL)
313  {
314  EPQState *epqstate = estate->es_epq_active;
315  Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
316 
317  if (scanrelid > 0)
318  epqstate->relsubs_done[scanrelid - 1] =
319  epqstate->relsubs_blocked[scanrelid - 1];
320  else
321  {
322  Bitmapset *relids;
323  int rtindex = -1;
324 
325  /*
326  * If an FDW or custom scan provider has replaced the join with a
327  * scan, there are multiple RTIs; reset the epqScanDone flag for
328  * all of them.
329  */
330  if (IsA(node->ps.plan, ForeignScan))
331  relids = ((ForeignScan *) node->ps.plan)->fs_base_relids;
332  else if (IsA(node->ps.plan, CustomScan))
333  relids = ((CustomScan *) node->ps.plan)->custom_relids;
334  else
335  elog(ERROR, "unexpected scan node: %d",
336  (int) nodeTag(node->ps.plan));
337 
338  while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
339  {
340  Assert(rtindex > 0);
341  epqstate->relsubs_done[rtindex - 1] =
342  epqstate->relsubs_blocked[rtindex - 1];
343  }
344  }
345  }
346 }
int bms_next_member(const Bitmapset *a, int prevbit)
Definition: bitmapset.c:1106
unsigned int Index
Definition: c.h:603
#define ERROR
Definition: elog.h:39
bool EvalPlanQualFetchRowMark(EPQState *epqstate, Index rti, TupleTableSlot *slot)
Definition: execMain.c:2650
void ExecAssignScanProjectionInfoWithVarno(ScanState *node, int varno)
Definition: execScan.c:284
static TupleTableSlot * ExecScanFetch(ScanState *node, ExecScanAccessMtd accessMtd, ExecScanRecheckMtd recheckMtd)
Definition: execScan.c:35
TupleTableSlot * ExecScan(ScanState *node, ExecScanAccessMtd accessMtd, ExecScanRecheckMtd recheckMtd)
Definition: execScan.c:157
void ExecAssignScanProjectionInfo(ScanState *node)
Definition: execScan.c:271
void ExecScanReScan(ScanState *node)
Definition: execScan.c:298
void ExecConditionalAssignProjectionInfo(PlanState *planstate, TupleDesc inputDesc, int varno)
Definition: execUtils.c:563
#define InstrCountFiltered1(node, delta)
Definition: execnodes.h:1140
static TupleTableSlot * ExecProject(ProjectionInfo *projInfo)
Definition: executor.h:375
#define ResetExprContext(econtext)
Definition: executor.h:543
TupleTableSlot *(* ExecScanAccessMtd)(ScanState *node)
Definition: executor.h:472
static bool ExecQual(ExprState *state, ExprContext *econtext)
Definition: executor.h:412
bool(* ExecScanRecheckMtd)(ScanState *node, TupleTableSlot *slot)
Definition: executor.h:473
Assert(fmt[strlen(fmt) - 1] !='\n')
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:121
#define IsA(nodeptr, _type_)
Definition: nodes.h:179
#define nodeTag(nodeptr)
Definition: nodes.h:133
ExecAuxRowMark ** relsubs_rowmark
Definition: execnodes.h:1211
TupleTableSlot ** relsubs_slot
Definition: execnodes.h:1183
bool * relsubs_blocked
Definition: execnodes.h:1227
bool * relsubs_done
Definition: execnodes.h:1218
struct EPQState * es_epq_active
Definition: execnodes.h:690
TupleTableSlot * ecxt_scantuple
Definition: execnodes.h:248
TupleTableSlot * resultslot
Definition: execnodes.h:96
ExprState * qual
Definition: execnodes.h:1057
Plan * plan
Definition: execnodes.h:1036
EState * state
Definition: execnodes.h:1038
ExprContext * ps_ExprContext
Definition: execnodes.h:1075
ProjectionInfo * ps_ProjInfo
Definition: execnodes.h:1076
ExprState pi_state
Definition: execnodes.h:355
TupleTableSlot * ss_ScanTupleSlot
Definition: execnodes.h:1476
PlanState ps
Definition: execnodes.h:1473
Index scanrelid
Definition: plannodes.h:387
TupleDesc tts_tupleDescriptor
Definition: tuptable.h:123
static TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: tuptable.h:433
#define TupIsNull(slot)
Definition: tuptable.h:300