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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) 1996-2018, 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_epqTuple != NULL)
44  {
45  /*
46  * We are inside an EvalPlanQual recheck. Return the test tuple if
47  * one is available, after rechecking any access-method-specific
48  * conditions.
49  */
50  Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
51 
52  if (scanrelid == 0)
53  {
54  TupleTableSlot *slot = node->ss_ScanTupleSlot;
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  if (!(*recheckMtd) (node, slot))
63  ExecClearTuple(slot); /* would not be returned by scan */
64  return slot;
65  }
66  else if (estate->es_epqTupleSet[scanrelid - 1])
67  {
68  TupleTableSlot *slot = node->ss_ScanTupleSlot;
69 
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;
75 
76  /* Return empty slot if we haven't got a test tuple */
77  if (estate->es_epqTuple[scanrelid - 1] == NULL)
78  return ExecClearTuple(slot);
79 
80  /* Store test tuple in the plan node's scan slot */
81  ExecStoreTuple(estate->es_epqTuple[scanrelid - 1],
82  slot, InvalidBuffer, false);
83 
84  /* Check if it meets the access-method conditions */
85  if (!(*recheckMtd) (node, slot))
86  ExecClearTuple(slot); /* would not be returned by scan */
87 
88  return slot;
89  }
90  }
91 
92  /*
93  * Run the node-type-specific access method function to get the next tuple
94  */
95  return (*accessMtd) (node);
96 }
97 
98 /* ----------------------------------------------------------------
99  * ExecScan
100  *
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.
106  *
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.
110  *
111  * Conditions:
112  * -- the "cursor" maintained by the AMI is positioned at the tuple
113  * returned previously.
114  *
115  * Initial States:
116  * -- the relation indicated is opened for scanning so that the
117  * "cursor" is positioned before the first qualifying tuple.
118  * ----------------------------------------------------------------
119  */
122  ExecScanAccessMtd accessMtd, /* function returning a tuple */
123  ExecScanRecheckMtd recheckMtd)
124 {
125  ExprContext *econtext;
126  ExprState *qual;
127  ProjectionInfo *projInfo;
128 
129  /*
130  * Fetch data from node
131  */
132  qual = node->ps.qual;
133  projInfo = node->ps.ps_ProjInfo;
134  econtext = node->ps.ps_ExprContext;
135 
136  /* interrupt checks are in ExecScanFetch */
137 
138  /*
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.
141  */
142  if (!qual && !projInfo)
143  {
144  ResetExprContext(econtext);
145  return ExecScanFetch(node, accessMtd, recheckMtd);
146  }
147 
148  /*
149  * Reset per-tuple memory context to free any expression evaluation
150  * storage allocated in the previous tuple cycle.
151  */
152  ResetExprContext(econtext);
153 
154  /*
155  * get a tuple from the access method. Loop until we obtain a tuple that
156  * passes the qualification.
157  */
158  for (;;)
159  {
160  TupleTableSlot *slot;
161 
162  slot = ExecScanFetch(node, accessMtd, recheckMtd);
163 
164  /*
165  * if the slot returned by the accessMtd contains NULL, then it means
166  * there is nothing more to scan so we just return an empty slot,
167  * being careful to use the projection result slot so it has correct
168  * tupleDesc.
169  */
170  if (TupIsNull(slot))
171  {
172  if (projInfo)
173  return ExecClearTuple(projInfo->pi_state.resultslot);
174  else
175  return slot;
176  }
177 
178  /*
179  * place the current tuple into the expr context
180  */
181  econtext->ecxt_scantuple = slot;
182 
183  /*
184  * check that the current tuple satisfies the qual-clause
185  *
186  * check for non-null qual here to avoid a function call to ExecQual()
187  * when the qual is null ... saves only a few cycles, but they add up
188  * ...
189  */
190  if (qual == NULL || ExecQual(qual, econtext))
191  {
192  /*
193  * Found a satisfactory scan tuple.
194  */
195  if (projInfo)
196  {
197  /*
198  * Form a projection tuple, store it in the result tuple slot
199  * and return it.
200  */
201  return ExecProject(projInfo);
202  }
203  else
204  {
205  /*
206  * Here, we aren't projecting, so just return scan tuple.
207  */
208  return slot;
209  }
210  }
211  else
212  InstrCountFiltered1(node, 1);
213 
214  /*
215  * Tuple fails qual, so free per-tuple memory and try again.
216  */
217  ResetExprContext(econtext);
218  }
219 }
220 
221 /*
222  * ExecAssignScanProjectionInfo
223  * Set up projection info for a scan node, if necessary.
224  *
225  * We can avoid a projection step if the requested tlist exactly matches
226  * the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
227  * Note that this case occurs not only for simple "SELECT * FROM ...", but
228  * also in most cases where there are joins or other processing nodes above
229  * the scan node, because the planner will preferentially generate a matching
230  * tlist.
231  *
232  * The scan slot's descriptor must have been set already.
233  */
234 void
236 {
237  Scan *scan = (Scan *) node->ps.plan;
239 
240  ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
241 }
242 
243 /*
244  * ExecAssignScanProjectionInfoWithVarno
245  * As above, but caller can specify varno expected in Vars in the tlist.
246  */
247 void
249 {
251 
252  ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
253 }
254 
255 /*
256  * ExecScanReScan
257  *
258  * This must be called within the ReScan function of any plan node type
259  * that uses ExecScan().
260  */
261 void
263 {
264  EState *estate = node->ps.state;
265 
266  /* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
267  if (estate->es_epqScanDone != NULL)
268  {
269  Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
270 
271  if (scanrelid > 0)
272  estate->es_epqScanDone[scanrelid - 1] = false;
273  else
274  {
275  Bitmapset *relids;
276  int rtindex = -1;
277 
278  /*
279  * If an FDW or custom scan provider has replaced the join with a
280  * scan, there are multiple RTIs; reset the epqScanDone flag for
281  * all of them.
282  */
283  if (IsA(node->ps.plan, ForeignScan))
284  relids = ((ForeignScan *) node->ps.plan)->fs_relids;
285  else if (IsA(node->ps.plan, CustomScan))
286  relids = ((CustomScan *) node->ps.plan)->custom_relids;
287  else
288  elog(ERROR, "unexpected scan node: %d",
289  (int) nodeTag(node->ps.plan));
290 
291  while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
292  {
293  Assert(rtindex > 0);
294  estate->es_epqScanDone[rtindex - 1] = false;
295  }
296  }
297  }
298 }
TupleTableSlot * ExecStoreTuple(HeapTuple tuple, TupleTableSlot *slot, Buffer buffer, bool shouldFree)
Definition: execTuples.c:356
HeapTuple * es_epqTuple
Definition: execnodes.h:558
#define IsA(nodeptr, _type_)
Definition: nodes.h:567
Index scanrelid
Definition: plannodes.h:343
ProjectionInfo * ps_ProjInfo
Definition: execnodes.h:948
static TupleTableSlot * ExecScanFetch(ScanState *node, ExecScanAccessMtd accessMtd, ExecScanRecheckMtd recheckMtd)
Definition: execScan.c:35
TupleTableSlot * ExecScan(ScanState *node, ExecScanAccessMtd accessMtd, ExecScanRecheckMtd recheckMtd)
Definition: execScan.c:121
ExprContext * ps_ExprContext
Definition: execnodes.h:947
int bms_next_member(const Bitmapset *a, int prevbit)
Definition: bitmapset.c:1075
TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: execTuples.c:475
#define InvalidBuffer
Definition: buf.h:25
TupleTableSlot * ss_ScanTupleSlot
Definition: execnodes.h:1195
EState * state
Definition: execnodes.h:914
TupleTableSlot * resultslot
Definition: execnodes.h:76
static bool ExecQual(ExprState *state, ExprContext *econtext)
Definition: executor.h:360
void ExecConditionalAssignProjectionInfo(PlanState *planstate, TupleDesc inputDesc, Index varno)
Definition: execUtils.c:476
void ExecAssignScanProjectionInfoWithVarno(ScanState *node, Index varno)
Definition: execScan.c:248
PlanState ps
Definition: execnodes.h:1192
#define ERROR
Definition: elog.h:43
void ExecAssignScanProjectionInfo(ScanState *node)
Definition: execScan.c:235
#define TupIsNull(slot)
Definition: tuptable.h:146
#define InstrCountFiltered1(node, delta)
Definition: execnodes.h:974
bool(* ExecScanRecheckMtd)(ScanState *node, TupleTableSlot *slot)
Definition: executor.h:421
TupleDesc tts_tupleDescriptor
Definition: tuptable.h:124
unsigned int Index
Definition: c.h:442
Plan * plan
Definition: execnodes.h:912
#define Assert(condition)
Definition: c.h:699
TupleTableSlot * ecxt_scantuple
Definition: execnodes.h:218
bool * es_epqTupleSet
Definition: execnodes.h:559
#define nodeTag(nodeptr)
Definition: nodes.h:521
ExprState * qual
Definition: execnodes.h:930
bool * es_epqScanDone
Definition: execnodes.h:560
void ExecScanReScan(ScanState *node)
Definition: execScan.c:262
ExprState pi_state
Definition: execnodes.h:325
#define CHECK_FOR_INTERRUPTS()
Definition: miscadmin.h:98
#define elog
Definition: elog.h:219
TupleTableSlot *(* ExecScanAccessMtd)(ScanState *node)
Definition: executor.h:420
static TupleTableSlot * ExecProject(ProjectionInfo *projInfo)
Definition: executor.h:323
#define ResetExprContext(econtext)
Definition: executor.h:482