PostgreSQL Source Code  git master
 All Data Structures Namespaces Files Functions Variables Typedefs Enumerations Enumerator Macros
nodeSeqscan.c
Go to the documentation of this file.
1 /*-------------------------------------------------------------------------
2  *
3  * nodeSeqscan.c
4  * Support routines for sequential scans of relations.
5  *
6  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/executor/nodeSeqscan.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 /*
16  * INTERFACE ROUTINES
17  * ExecSeqScan sequentially scans a relation.
18  * ExecSeqNext retrieve next tuple in sequential order.
19  * ExecInitSeqScan creates and initializes a seqscan node.
20  * ExecEndSeqScan releases any storage allocated.
21  * ExecReScanSeqScan rescans the relation
22  *
23  * ExecSeqScanEstimate estimates DSM space needed for parallel scan
24  * ExecSeqScanInitializeDSM initialize DSM for parallel scan
25  * ExecSeqScanInitializeWorker attach to DSM info in parallel worker
26  */
27 #include "postgres.h"
28 
29 #include "access/relscan.h"
30 #include "executor/execdebug.h"
31 #include "executor/nodeSeqscan.h"
32 #include "utils/rel.h"
33 
34 static void InitScanRelation(SeqScanState *node, EState *estate, int eflags);
35 static TupleTableSlot *SeqNext(SeqScanState *node);
36 
37 /* ----------------------------------------------------------------
38  * Scan Support
39  * ----------------------------------------------------------------
40  */
41 
42 /* ----------------------------------------------------------------
43  * SeqNext
44  *
45  * This is a workhorse for ExecSeqScan
46  * ----------------------------------------------------------------
47  */
48 static TupleTableSlot *
50 {
51  HeapTuple tuple;
52  HeapScanDesc scandesc;
53  EState *estate;
54  ScanDirection direction;
55  TupleTableSlot *slot;
56 
57  /*
58  * get information from the estate and scan state
59  */
60  scandesc = node->ss.ss_currentScanDesc;
61  estate = node->ss.ps.state;
62  direction = estate->es_direction;
63  slot = node->ss.ss_ScanTupleSlot;
64 
65  if (scandesc == NULL)
66  {
67  /*
68  * We reach here if the scan is not parallel, or if we're executing a
69  * scan that was intended to be parallel serially.
70  */
71  scandesc = heap_beginscan(node->ss.ss_currentRelation,
72  estate->es_snapshot,
73  0, NULL);
74  node->ss.ss_currentScanDesc = scandesc;
75  }
76 
77  /*
78  * get the next tuple from the table
79  */
80  tuple = heap_getnext(scandesc, direction);
81 
82  /*
83  * save the tuple and the buffer returned to us by the access methods in
84  * our scan tuple slot and return the slot. Note: we pass 'false' because
85  * tuples returned by heap_getnext() are pointers onto disk pages and were
86  * not created with palloc() and so should not be pfree()'d. Note also
87  * that ExecStoreTuple will increment the refcount of the buffer; the
88  * refcount will not be dropped until the tuple table slot is cleared.
89  */
90  if (tuple)
91  ExecStoreTuple(tuple, /* tuple to store */
92  slot, /* slot to store in */
93  scandesc->rs_cbuf, /* buffer associated with this
94  * tuple */
95  false); /* don't pfree this pointer */
96  else
97  ExecClearTuple(slot);
98 
99  return slot;
100 }
101 
102 /*
103  * SeqRecheck -- access method routine to recheck a tuple in EvalPlanQual
104  */
105 static bool
107 {
108  /*
109  * Note that unlike IndexScan, SeqScan never use keys in heap_beginscan
110  * (and this is very bad) - so, here we do not check are keys ok or not.
111  */
112  return true;
113 }
114 
115 /* ----------------------------------------------------------------
116  * ExecSeqScan(node)
117  *
118  * Scans the relation sequentially and returns the next qualifying
119  * tuple.
120  * We call the ExecScan() routine and pass it the appropriate
121  * access method functions.
122  * ----------------------------------------------------------------
123  */
126 {
127  return ExecScan((ScanState *) node,
130 }
131 
132 /* ----------------------------------------------------------------
133  * InitScanRelation
134  *
135  * Set up to access the scan relation.
136  * ----------------------------------------------------------------
137  */
138 static void
139 InitScanRelation(SeqScanState *node, EState *estate, int eflags)
140 {
141  Relation currentRelation;
142 
143  /*
144  * get the relation object id from the relid'th entry in the range table,
145  * open that relation and acquire appropriate lock on it.
146  */
147  currentRelation = ExecOpenScanRelation(estate,
148  ((SeqScan *) node->ss.ps.plan)->scanrelid,
149  eflags);
150 
151  node->ss.ss_currentRelation = currentRelation;
152 
153  /* and report the scan tuple slot's rowtype */
154  ExecAssignScanType(&node->ss, RelationGetDescr(currentRelation));
155 }
156 
157 
158 /* ----------------------------------------------------------------
159  * ExecInitSeqScan
160  * ----------------------------------------------------------------
161  */
162 SeqScanState *
163 ExecInitSeqScan(SeqScan *node, EState *estate, int eflags)
164 {
165  SeqScanState *scanstate;
166 
167  /*
168  * Once upon a time it was possible to have an outerPlan of a SeqScan, but
169  * not any more.
170  */
171  Assert(outerPlan(node) == NULL);
172  Assert(innerPlan(node) == NULL);
173 
174  /*
175  * create state structure
176  */
177  scanstate = makeNode(SeqScanState);
178  scanstate->ss.ps.plan = (Plan *) node;
179  scanstate->ss.ps.state = estate;
180 
181  /*
182  * Miscellaneous initialization
183  *
184  * create expression context for node
185  */
186  ExecAssignExprContext(estate, &scanstate->ss.ps);
187 
188  /*
189  * initialize child expressions
190  */
191  scanstate->ss.ps.qual =
192  ExecInitQual(node->plan.qual, (PlanState *) scanstate);
193 
194  /*
195  * tuple table initialization
196  */
197  ExecInitResultTupleSlot(estate, &scanstate->ss.ps);
198  ExecInitScanTupleSlot(estate, &scanstate->ss);
199 
200  /*
201  * initialize scan relation
202  */
203  InitScanRelation(scanstate, estate, eflags);
204 
205  /*
206  * Initialize result tuple type and projection info.
207  */
208  ExecAssignResultTypeFromTL(&scanstate->ss.ps);
209  ExecAssignScanProjectionInfo(&scanstate->ss);
210 
211  return scanstate;
212 }
213 
214 /* ----------------------------------------------------------------
215  * ExecEndSeqScan
216  *
217  * frees any storage allocated through C routines.
218  * ----------------------------------------------------------------
219  */
220 void
222 {
223  Relation relation;
224  HeapScanDesc scanDesc;
225 
226  /*
227  * get information from node
228  */
229  relation = node->ss.ss_currentRelation;
230  scanDesc = node->ss.ss_currentScanDesc;
231 
232  /*
233  * Free the exprcontext
234  */
235  ExecFreeExprContext(&node->ss.ps);
236 
237  /*
238  * clean out the tuple table
239  */
242 
243  /*
244  * close heap scan
245  */
246  if (scanDesc != NULL)
247  heap_endscan(scanDesc);
248 
249  /*
250  * close the heap relation.
251  */
252  ExecCloseScanRelation(relation);
253 }
254 
255 /* ----------------------------------------------------------------
256  * Join Support
257  * ----------------------------------------------------------------
258  */
259 
260 /* ----------------------------------------------------------------
261  * ExecReScanSeqScan
262  *
263  * Rescans the relation.
264  * ----------------------------------------------------------------
265  */
266 void
268 {
269  HeapScanDesc scan;
270 
271  scan = node->ss.ss_currentScanDesc;
272 
273  if (scan != NULL)
274  heap_rescan(scan, /* scan desc */
275  NULL); /* new scan keys */
276 
277  ExecScanReScan((ScanState *) node);
278 }
279 
280 /* ----------------------------------------------------------------
281  * Parallel Scan Support
282  * ----------------------------------------------------------------
283  */
284 
285 /* ----------------------------------------------------------------
286  * ExecSeqScanEstimate
287  *
288  * estimates the space required to serialize seqscan node.
289  * ----------------------------------------------------------------
290  */
291 void
293  ParallelContext *pcxt)
294 {
295  EState *estate = node->ss.ps.state;
296 
299  shm_toc_estimate_keys(&pcxt->estimator, 1);
300 }
301 
302 /* ----------------------------------------------------------------
303  * ExecSeqScanInitializeDSM
304  *
305  * Set up a parallel heap scan descriptor.
306  * ----------------------------------------------------------------
307  */
308 void
310  ParallelContext *pcxt)
311 {
312  EState *estate = node->ss.ps.state;
313  ParallelHeapScanDesc pscan;
314 
315  pscan = shm_toc_allocate(pcxt->toc, node->pscan_len);
317  node->ss.ss_currentRelation,
318  estate->es_snapshot);
319  shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pscan);
320  node->ss.ss_currentScanDesc =
322 }
323 
324 /* ----------------------------------------------------------------
325  * ExecSeqScanInitializeWorker
326  *
327  * Copy relevant information from TOC into planstate.
328  * ----------------------------------------------------------------
329  */
330 void
332 {
333  ParallelHeapScanDesc pscan;
334 
335  pscan = shm_toc_lookup(toc, node->ss.ps.plan->plan_node_id, false);
336  node->ss.ss_currentScanDesc =
338 }
void ExecSeqScanInitializeWorker(SeqScanState *node, shm_toc *toc)
Definition: nodeSeqscan.c:331
TupleTableSlot * ExecStoreTuple(HeapTuple tuple, TupleTableSlot *slot, Buffer buffer, bool shouldFree)
Definition: execTuples.c:320
List * qual
Definition: plannodes.h:145
Plan plan
Definition: plannodes.h:328
void ExecInitScanTupleSlot(EState *estate, ScanState *scanstate)
Definition: execTuples.c:842
void heap_endscan(HeapScanDesc scan)
Definition: heapam.c:1578
#define RelationGetDescr(relation)
Definition: rel.h:428
TupleTableSlot * ExecScan(ScanState *node, ExecScanAccessMtd accessMtd, ExecScanRecheckMtd recheckMtd)
Definition: execScan.c:121
shm_toc_estimator estimator
Definition: parallel.h:41
TupleTableSlot * ExecClearTuple(TupleTableSlot *slot)
Definition: execTuples.c:439
int plan_node_id
Definition: plannodes.h:143
static void InitScanRelation(SeqScanState *node, EState *estate, int eflags)
Definition: nodeSeqscan.c:139
Snapshot es_snapshot
Definition: execnodes.h:429
ScanState ss
Definition: execnodes.h:1087
TupleTableSlot * ss_ScanTupleSlot
Definition: execnodes.h:1078
Relation ss_currentRelation
Definition: execnodes.h:1076
EState * state
Definition: execnodes.h:834
#define shm_toc_estimate_chunk(e, sz)
Definition: shm_toc.h:51
static TupleTableSlot * SeqNext(SeqScanState *node)
Definition: nodeSeqscan.c:49
void ExecFreeExprContext(PlanState *planstate)
Definition: execUtils.c:516
Size pscan_len
Definition: execnodes.h:1088
ScanDirection es_direction
Definition: execnodes.h:428
ExprState * ExecInitQual(List *qual, PlanState *parent)
Definition: execExpr.c:160
void ExecAssignResultTypeFromTL(PlanState *planstate)
Definition: execUtils.c:440
TupleTableSlot *(* ExecScanAccessMtd)(ScanState *node)
Definition: executor.h:389
PlanState ps
Definition: execnodes.h:1075
bool(* ExecScanRecheckMtd)(ScanState *node, TupleTableSlot *slot)
Definition: executor.h:390
TupleTableSlot * ps_ResultTupleSlot
Definition: execnodes.h:861
void ExecSeqScanInitializeDSM(SeqScanState *node, ParallelContext *pcxt)
Definition: nodeSeqscan.c:309
void ExecAssignScanProjectionInfo(ScanState *node)
Definition: execScan.c:235
void ExecInitResultTupleSlot(EState *estate, PlanState *planstate)
Definition: execTuples.c:832
Relation ExecOpenScanRelation(EState *estate, Index scanrelid, int eflags)
Definition: execUtils.c:603
#define innerPlan(node)
Definition: plannodes.h:173
ScanDirection
Definition: sdir.h:22
void heap_rescan(HeapScanDesc scan, ScanKey key)
Definition: heapam.c:1515
void ExecEndSeqScan(SeqScanState *node)
Definition: nodeSeqscan.c:221
#define outerPlan(node)
Definition: plannodes.h:174
void heap_parallelscan_initialize(ParallelHeapScanDesc target, Relation relation, Snapshot snapshot)
Definition: heapam.c:1628
HeapTuple heap_getnext(HeapScanDesc scan, ScanDirection direction)
Definition: heapam.c:1794
Plan * plan
Definition: execnodes.h:832
Buffer rs_cbuf
Definition: relscan.h:70
#define makeNode(_type_)
Definition: nodes.h:557
#define NULL
Definition: c.h:229
#define Assert(condition)
Definition: c.h:675
void ExecAssignExprContext(EState *estate, PlanState *planstate)
Definition: execUtils.c:418
void ExecSeqScanEstimate(SeqScanState *node, ParallelContext *pcxt)
Definition: nodeSeqscan.c:292
#define shm_toc_estimate_keys(e, cnt)
Definition: shm_toc.h:53
void ExecCloseScanRelation(Relation scanrel)
Definition: execUtils.c:661
void * shm_toc_allocate(shm_toc *toc, Size nbytes)
Definition: shm_toc.c:83
ExprState * qual
Definition: execnodes.h:846
TupleTableSlot * ExecSeqScan(SeqScanState *node)
Definition: nodeSeqscan.c:125
static bool SeqRecheck(SeqScanState *node, TupleTableSlot *slot)
Definition: nodeSeqscan.c:106
HeapScanDesc ss_currentScanDesc
Definition: execnodes.h:1077
void shm_toc_insert(shm_toc *toc, uint64 key, void *address)
Definition: shm_toc.c:161
SeqScanState * ExecInitSeqScan(SeqScan *node, EState *estate, int eflags)
Definition: nodeSeqscan.c:163
void ExecScanReScan(ScanState *node)
Definition: execScan.c:327
void ExecAssignScanType(ScanState *scanstate, TupleDesc tupDesc)
Definition: execUtils.c:540
Size heap_parallelscan_estimate(Snapshot snapshot)
Definition: heapam.c:1613
HeapScanDesc heap_beginscan_parallel(Relation relation, ParallelHeapScanDesc parallel_scan)
Definition: heapam.c:1650
HeapScanDesc heap_beginscan(Relation relation, Snapshot snapshot, int nkeys, ScanKey key)
Definition: heapam.c:1391
void * shm_toc_lookup(shm_toc *toc, uint64 key, bool noError)
Definition: shm_toc.c:222
shm_toc * toc
Definition: parallel.h:44
void ExecReScanSeqScan(SeqScanState *node)
Definition: nodeSeqscan.c:267