PostgreSQL Source Code  git master
nodeTidscan.c
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1 /*-------------------------------------------------------------------------
2  *
3  * nodeTidscan.c
4  * Routines to support direct tid scans of relations
5  *
6  * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
7  * Portions Copyright (c) 1994, Regents of the University of California
8  *
9  *
10  * IDENTIFICATION
11  * src/backend/executor/nodeTidscan.c
12  *
13  *-------------------------------------------------------------------------
14  */
15 /*
16  * INTERFACE ROUTINES
17  *
18  * ExecTidScan scans a relation using tids
19  * ExecInitTidScan creates and initializes state info.
20  * ExecReScanTidScan rescans the tid relation.
21  * ExecEndTidScan releases all storage.
22  */
23 #include "postgres.h"
24 
25 #include "access/sysattr.h"
26 #include "access/tableam.h"
27 #include "catalog/pg_type.h"
28 #include "executor/execdebug.h"
29 #include "executor/nodeTidscan.h"
30 #include "miscadmin.h"
31 #include "nodes/nodeFuncs.h"
32 #include "storage/bufmgr.h"
33 #include "utils/array.h"
34 #include "utils/rel.h"
35 
36 
37 #define IsCTIDVar(node) \
38  ((node) != NULL && \
39  IsA((node), Var) && \
40  ((Var *) (node))->varattno == SelfItemPointerAttributeNumber && \
41  ((Var *) (node))->varlevelsup == 0)
42 
43 /* one element in tss_tidexprs */
44 typedef struct TidExpr
45 {
46  ExprState *exprstate; /* ExprState for a TID-yielding subexpr */
47  bool isarray; /* if true, it yields tid[] not just tid */
48  CurrentOfExpr *cexpr; /* alternatively, we can have CURRENT OF */
49 } TidExpr;
50 
51 static void TidExprListCreate(TidScanState *tidstate);
52 static void TidListEval(TidScanState *tidstate);
53 static int itemptr_comparator(const void *a, const void *b);
54 static TupleTableSlot *TidNext(TidScanState *node);
55 
56 
57 /*
58  * Extract the qual subexpressions that yield TIDs to search for,
59  * and compile them into ExprStates if they're ordinary expressions.
60  *
61  * CURRENT OF is a special case that we can't compile usefully;
62  * just drop it into the TidExpr list as-is.
63  */
64 static void
66 {
67  TidScan *node = (TidScan *) tidstate->ss.ps.plan;
68  ListCell *l;
69 
70  tidstate->tss_tidexprs = NIL;
71  tidstate->tss_isCurrentOf = false;
72 
73  foreach(l, node->tidquals)
74  {
75  Expr *expr = (Expr *) lfirst(l);
76  TidExpr *tidexpr = (TidExpr *) palloc0(sizeof(TidExpr));
77 
78  if (is_opclause(expr))
79  {
80  Node *arg1;
81  Node *arg2;
82 
83  arg1 = get_leftop(expr);
84  arg2 = get_rightop(expr);
85  if (IsCTIDVar(arg1))
86  tidexpr->exprstate = ExecInitExpr((Expr *) arg2,
87  &tidstate->ss.ps);
88  else if (IsCTIDVar(arg2))
89  tidexpr->exprstate = ExecInitExpr((Expr *) arg1,
90  &tidstate->ss.ps);
91  else
92  elog(ERROR, "could not identify CTID variable");
93  tidexpr->isarray = false;
94  }
95  else if (expr && IsA(expr, ScalarArrayOpExpr))
96  {
97  ScalarArrayOpExpr *saex = (ScalarArrayOpExpr *) expr;
98 
99  Assert(IsCTIDVar(linitial(saex->args)));
100  tidexpr->exprstate = ExecInitExpr(lsecond(saex->args),
101  &tidstate->ss.ps);
102  tidexpr->isarray = true;
103  }
104  else if (expr && IsA(expr, CurrentOfExpr))
105  {
106  CurrentOfExpr *cexpr = (CurrentOfExpr *) expr;
107 
108  tidexpr->cexpr = cexpr;
109  tidstate->tss_isCurrentOf = true;
110  }
111  else
112  elog(ERROR, "could not identify CTID expression");
113 
114  tidstate->tss_tidexprs = lappend(tidstate->tss_tidexprs, tidexpr);
115  }
116 
117  /* CurrentOfExpr could never appear OR'd with something else */
118  Assert(list_length(tidstate->tss_tidexprs) == 1 ||
119  !tidstate->tss_isCurrentOf);
120 }
121 
122 /*
123  * Compute the list of TIDs to be visited, by evaluating the expressions
124  * for them.
125  *
126  * (The result is actually an array, not a list.)
127  */
128 static void
130 {
131  ExprContext *econtext = tidstate->ss.ps.ps_ExprContext;
132  TableScanDesc scan;
133  ItemPointerData *tidList;
134  int numAllocTids;
135  int numTids;
136  ListCell *l;
137 
138  /*
139  * Start scan on-demand - initializing a scan isn't free (e.g. heap stats
140  * the size of the table), so it makes sense to delay that until needed -
141  * the node might never get executed.
142  */
143  if (tidstate->ss.ss_currentScanDesc == NULL)
144  tidstate->ss.ss_currentScanDesc =
146  tidstate->ss.ps.state->es_snapshot,
147  0, NULL);
148  scan = tidstate->ss.ss_currentScanDesc;
149 
150  /*
151  * We initialize the array with enough slots for the case that all quals
152  * are simple OpExprs or CurrentOfExprs. If there are any
153  * ScalarArrayOpExprs, we may have to enlarge the array.
154  */
155  numAllocTids = list_length(tidstate->tss_tidexprs);
156  tidList = (ItemPointerData *)
157  palloc(numAllocTids * sizeof(ItemPointerData));
158  numTids = 0;
159 
160  foreach(l, tidstate->tss_tidexprs)
161  {
162  TidExpr *tidexpr = (TidExpr *) lfirst(l);
163  ItemPointer itemptr;
164  bool isNull;
165 
166  if (tidexpr->exprstate && !tidexpr->isarray)
167  {
168  itemptr = (ItemPointer)
170  econtext,
171  &isNull));
172  if (isNull)
173  continue;
174 
175  /*
176  * We silently discard any TIDs that the AM considers invalid
177  * (E.g. for heap, they could be out of range at the time of scan
178  * start. Since we hold at least AccessShareLock on the table, it
179  * won't be possible for someone to truncate away the blocks we
180  * intend to visit.).
181  */
182  if (!table_tuple_tid_valid(scan, itemptr))
183  continue;
184 
185  if (numTids >= numAllocTids)
186  {
187  numAllocTids *= 2;
188  tidList = (ItemPointerData *)
189  repalloc(tidList,
190  numAllocTids * sizeof(ItemPointerData));
191  }
192  tidList[numTids++] = *itemptr;
193  }
194  else if (tidexpr->exprstate && tidexpr->isarray)
195  {
196  Datum arraydatum;
197  ArrayType *itemarray;
198  Datum *ipdatums;
199  bool *ipnulls;
200  int ndatums;
201  int i;
202 
203  arraydatum = ExecEvalExprSwitchContext(tidexpr->exprstate,
204  econtext,
205  &isNull);
206  if (isNull)
207  continue;
208  itemarray = DatumGetArrayTypeP(arraydatum);
209  deconstruct_array(itemarray,
210  TIDOID, sizeof(ItemPointerData), false, 's',
211  &ipdatums, &ipnulls, &ndatums);
212  if (numTids + ndatums > numAllocTids)
213  {
214  numAllocTids = numTids + ndatums;
215  tidList = (ItemPointerData *)
216  repalloc(tidList,
217  numAllocTids * sizeof(ItemPointerData));
218  }
219  for (i = 0; i < ndatums; i++)
220  {
221  if (ipnulls[i])
222  continue;
223 
224  itemptr = (ItemPointer) DatumGetPointer(ipdatums[i]);
225 
226  if (!table_tuple_tid_valid(scan, itemptr))
227  continue;
228 
229  tidList[numTids++] = *itemptr;
230  }
231  pfree(ipdatums);
232  pfree(ipnulls);
233  }
234  else
235  {
236  ItemPointerData cursor_tid;
237 
238  Assert(tidexpr->cexpr);
239  if (execCurrentOf(tidexpr->cexpr, econtext,
241  &cursor_tid))
242  {
243  if (numTids >= numAllocTids)
244  {
245  numAllocTids *= 2;
246  tidList = (ItemPointerData *)
247  repalloc(tidList,
248  numAllocTids * sizeof(ItemPointerData));
249  }
250  tidList[numTids++] = cursor_tid;
251  }
252  }
253  }
254 
255  /*
256  * Sort the array of TIDs into order, and eliminate duplicates.
257  * Eliminating duplicates is necessary since we want OR semantics across
258  * the list. Sorting makes it easier to detect duplicates, and as a bonus
259  * ensures that we will visit the heap in the most efficient way.
260  */
261  if (numTids > 1)
262  {
263  int lastTid;
264  int i;
265 
266  /* CurrentOfExpr could never appear OR'd with something else */
267  Assert(!tidstate->tss_isCurrentOf);
268 
269  qsort((void *) tidList, numTids, sizeof(ItemPointerData),
271  lastTid = 0;
272  for (i = 1; i < numTids; i++)
273  {
274  if (!ItemPointerEquals(&tidList[lastTid], &tidList[i]))
275  tidList[++lastTid] = tidList[i];
276  }
277  numTids = lastTid + 1;
278  }
279 
280  tidstate->tss_TidList = tidList;
281  tidstate->tss_NumTids = numTids;
282  tidstate->tss_TidPtr = -1;
283 }
284 
285 /*
286  * qsort comparator for ItemPointerData items
287  */
288 static int
289 itemptr_comparator(const void *a, const void *b)
290 {
291  const ItemPointerData *ipa = (const ItemPointerData *) a;
292  const ItemPointerData *ipb = (const ItemPointerData *) b;
297 
298  if (ba < bb)
299  return -1;
300  if (ba > bb)
301  return 1;
302  if (oa < ob)
303  return -1;
304  if (oa > ob)
305  return 1;
306  return 0;
307 }
308 
309 /* ----------------------------------------------------------------
310  * TidNext
311  *
312  * Retrieve a tuple from the TidScan node's currentRelation
313  * using the tids in the TidScanState information.
314  *
315  * ----------------------------------------------------------------
316  */
317 static TupleTableSlot *
319 {
320  EState *estate;
321  ScanDirection direction;
322  Snapshot snapshot;
323  TableScanDesc scan;
324  Relation heapRelation;
325  TupleTableSlot *slot;
326  ItemPointerData *tidList;
327  int numTids;
328  bool bBackward;
329 
330  /*
331  * extract necessary information from tid scan node
332  */
333  estate = node->ss.ps.state;
334  direction = estate->es_direction;
335  snapshot = estate->es_snapshot;
336  heapRelation = node->ss.ss_currentRelation;
337  slot = node->ss.ss_ScanTupleSlot;
338 
339  /*
340  * First time through, compute the list of TIDs to be visited
341  */
342  if (node->tss_TidList == NULL)
343  TidListEval(node);
344 
345  scan = node->ss.ss_currentScanDesc;
346  tidList = node->tss_TidList;
347  numTids = node->tss_NumTids;
348 
349  /*
350  * Initialize or advance scan position, depending on direction.
351  */
352  bBackward = ScanDirectionIsBackward(direction);
353  if (bBackward)
354  {
355  if (node->tss_TidPtr < 0)
356  {
357  /* initialize for backward scan */
358  node->tss_TidPtr = numTids - 1;
359  }
360  else
361  node->tss_TidPtr--;
362  }
363  else
364  {
365  if (node->tss_TidPtr < 0)
366  {
367  /* initialize for forward scan */
368  node->tss_TidPtr = 0;
369  }
370  else
371  node->tss_TidPtr++;
372  }
373 
374  while (node->tss_TidPtr >= 0 && node->tss_TidPtr < numTids)
375  {
376  ItemPointerData tid = tidList[node->tss_TidPtr];
377 
378  /*
379  * For WHERE CURRENT OF, the tuple retrieved from the cursor might
380  * since have been updated; if so, we should fetch the version that is
381  * current according to our snapshot.
382  */
383  if (node->tss_isCurrentOf)
384  table_tuple_get_latest_tid(scan, &tid);
385 
386  if (table_tuple_fetch_row_version(heapRelation, &tid, snapshot, slot))
387  return slot;
388 
389  /* Bad TID or failed snapshot qual; try next */
390  if (bBackward)
391  node->tss_TidPtr--;
392  else
393  node->tss_TidPtr++;
394 
396  }
397 
398  /*
399  * if we get here it means the tid scan failed so we are at the end of the
400  * scan..
401  */
402  return ExecClearTuple(slot);
403 }
404 
405 /*
406  * TidRecheck -- access method routine to recheck a tuple in EvalPlanQual
407  */
408 static bool
410 {
411  /*
412  * XXX shouldn't we check here to make sure tuple matches TID list? In
413  * runtime-key case this is not certain, is it? However, in the WHERE
414  * CURRENT OF case it might not match anyway ...
415  */
416  return true;
417 }
418 
419 
420 /* ----------------------------------------------------------------
421  * ExecTidScan(node)
422  *
423  * Scans the relation using tids and returns
424  * the next qualifying tuple in the direction specified.
425  * We call the ExecScan() routine and pass it the appropriate
426  * access method functions.
427  *
428  * Conditions:
429  * -- the "cursor" maintained by the AMI is positioned at the tuple
430  * returned previously.
431  *
432  * Initial States:
433  * -- the relation indicated is opened for scanning so that the
434  * "cursor" is positioned before the first qualifying tuple.
435  * -- tss_TidPtr is -1.
436  * ----------------------------------------------------------------
437  */
438 static TupleTableSlot *
440 {
441  TidScanState *node = castNode(TidScanState, pstate);
442 
443  return ExecScan(&node->ss,
446 }
447 
448 /* ----------------------------------------------------------------
449  * ExecReScanTidScan(node)
450  * ----------------------------------------------------------------
451  */
452 void
454 {
455  if (node->tss_TidList)
456  pfree(node->tss_TidList);
457  node->tss_TidList = NULL;
458  node->tss_NumTids = 0;
459  node->tss_TidPtr = -1;
460 
461  /* not really necessary, but seems good form */
462  if (node->ss.ss_currentScanDesc)
463  table_rescan(node->ss.ss_currentScanDesc, NULL);
464 
465  ExecScanReScan(&node->ss);
466 }
467 
468 /* ----------------------------------------------------------------
469  * ExecEndTidScan
470  *
471  * Releases any storage allocated through C routines.
472  * Returns nothing.
473  * ----------------------------------------------------------------
474  */
475 void
477 {
478  if (node->ss.ss_currentScanDesc)
480 
481  /*
482  * Free the exprcontext
483  */
484  ExecFreeExprContext(&node->ss.ps);
485 
486  /*
487  * clear out tuple table slots
488  */
489  if (node->ss.ps.ps_ResultTupleSlot)
492 }
493 
494 /* ----------------------------------------------------------------
495  * ExecInitTidScan
496  *
497  * Initializes the tid scan's state information, creates
498  * scan keys, and opens the base and tid relations.
499  *
500  * Parameters:
501  * node: TidScan node produced by the planner.
502  * estate: the execution state initialized in InitPlan.
503  * ----------------------------------------------------------------
504  */
505 TidScanState *
506 ExecInitTidScan(TidScan *node, EState *estate, int eflags)
507 {
508  TidScanState *tidstate;
509  Relation currentRelation;
510 
511  /*
512  * create state structure
513  */
514  tidstate = makeNode(TidScanState);
515  tidstate->ss.ps.plan = (Plan *) node;
516  tidstate->ss.ps.state = estate;
517  tidstate->ss.ps.ExecProcNode = ExecTidScan;
518 
519  /*
520  * Miscellaneous initialization
521  *
522  * create expression context for node
523  */
524  ExecAssignExprContext(estate, &tidstate->ss.ps);
525 
526  /*
527  * mark tid list as not computed yet
528  */
529  tidstate->tss_TidList = NULL;
530  tidstate->tss_NumTids = 0;
531  tidstate->tss_TidPtr = -1;
532 
533  /*
534  * open the scan relation
535  */
536  currentRelation = ExecOpenScanRelation(estate, node->scan.scanrelid, eflags);
537 
538  tidstate->ss.ss_currentRelation = currentRelation;
539  tidstate->ss.ss_currentScanDesc = NULL; /* no heap scan here */
540 
541  /*
542  * get the scan type from the relation descriptor.
543  */
544  ExecInitScanTupleSlot(estate, &tidstate->ss,
545  RelationGetDescr(currentRelation),
546  table_slot_callbacks(currentRelation));
547 
548  /*
549  * Initialize result type and projection.
550  */
551  ExecInitResultTypeTL(&tidstate->ss.ps);
552  ExecAssignScanProjectionInfo(&tidstate->ss);
553 
554  /*
555  * initialize child expressions
556  */
557  tidstate->ss.ps.qual =
558  ExecInitQual(node->scan.plan.qual, (PlanState *) tidstate);
559 
560  TidExprListCreate(tidstate);
561 
562  /*
563  * all done.
564  */
565  return tidstate;
566 }
CurrentOfExpr * cexpr
Definition: nodeTidscan.c:48
#define NIL
Definition: pg_list.h:65
List * qual
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Plan plan
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