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Commit2ef172a

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Fix latent bug in ExecSeqRestrPos: it leaves the plan node's result slot
in an inconsistent state. (This is only latent because in realityExecSeqRestrPos is dead code at the moment ... but someday maybe it won'tbe.) Add some comments about what the API for plan node mark/restoreactually is, because it's not immediately obvious.
1 parenteb0d00a commit2ef172a

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4 files changed

+35
-10
lines changed

4 files changed

+35
-10
lines changed

‎src/backend/access/index/indexam.c

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.80 2005/04/14 20:03:23 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/access/index/indexam.c,v 1.81 2005/05/15 21:19:54 tgl Exp $
1212
*
1313
* INTERFACE ROUTINES
1414
*index_open- open an index relation by relation OID
@@ -411,6 +411,10 @@ index_markpos(IndexScanDesc scan)
411411

412412
/* ----------------
413413
*index_restrpos- restore a scan position
414+
*
415+
* NOTE: this only restores the internal scan state of the index AM.
416+
* The current result tuple (scan->xs_ctup) doesn't change. See comments
417+
* for ExecRestrPos().
414418
* ----------------
415419
*/
416420
void

‎src/backend/executor/execAmi.c

Lines changed: 14 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -6,7 +6,7 @@
66
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
9-
*$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.83 2005/04/19 22:35:11 tgl Exp $
9+
*$PostgreSQL: pgsql/src/backend/executor/execAmi.c,v 1.84 2005/05/15 21:19:54 tgl Exp $
1010
*
1111
*-------------------------------------------------------------------------
1212
*/
@@ -248,6 +248,14 @@ ExecMarkPos(PlanState *node)
248248
* ExecRestrPos
249249
*
250250
* restores the scan position previously saved with ExecMarkPos()
251+
*
252+
* NOTE: the semantics of this are that the first ExecProcNode following
253+
* the restore operation will yield the same tuple as the first one following
254+
* the mark operation. It is unspecified what happens to the plan node's
255+
* result TupleTableSlot. (In most cases the result slot is unchanged by
256+
* a restore, but the node may choose to clear it or to load it with the
257+
* restored-to tuple.) Hence the caller should discard any previously
258+
* returned TupleTableSlot after doing a restore.
251259
*/
252260
void
253261
ExecRestrPos(PlanState*node)
@@ -290,6 +298,11 @@ ExecRestrPos(PlanState *node)
290298
* XXX Ideally, all plan node types would support mark/restore, and this
291299
* wouldn't be needed. For now, this had better match the routines above.
292300
* But note the test is on Plan nodetype, not PlanState nodetype.
301+
*
302+
* (However, since the only present use of mark/restore is in mergejoin,
303+
* there is no need to support mark/restore in any plan type that is not
304+
* capable of generating ordered output. So the seqscan, tidscan, and
305+
* functionscan support is actually useless code at present.)
293306
*/
294307
bool
295308
ExecSupportsMarkRestore(NodeTagplantype)

‎src/backend/executor/nodeMergejoin.c

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/executor/nodeMergejoin.c,v 1.73 2005/05/14 21:29:23 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/executor/nodeMergejoin.c,v 1.74 2005/05/15 21:19:55 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -1134,8 +1134,10 @@ ExecMergeJoin(MergeJoinState *node)
11341134
ExecRestrPos(innerPlan);
11351135

11361136
/*
1137-
* ExecRestrPos really should give us back a new Slot,
1138-
* but since it doesn't, use the marked slot.
1137+
* ExecRestrPos probably should give us back a new Slot,
1138+
* but since it doesn't, use the marked slot. (The
1139+
* previously returned mj_InnerTupleSlot cannot be
1140+
* assumed to hold the required tuple.)
11391141
*/
11401142
node->mj_InnerTupleSlot=innerTupleSlot;
11411143
/* we need not do MJEvalInnerValues again */

‎src/backend/executor/nodeSeqscan.c

Lines changed: 11 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/executor/nodeSeqscan.c,v 1.52 2005/03/16 21:38:07 tgl Exp $
11+
* $PostgreSQL: pgsql/src/backend/executor/nodeSeqscan.c,v 1.53 2005/05/15 21:19:55 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -342,9 +342,8 @@ ExecSeqReScan(SeqScanState *node, ExprContext *exprCtxt)
342342
void
343343
ExecSeqMarkPos(SeqScanState*node)
344344
{
345-
HeapScanDescscan;
345+
HeapScanDescscan=node->ss_currentScanDesc;
346346

347-
scan=node->ss_currentScanDesc;
348347
heap_markpos(scan);
349348
}
350349

@@ -357,8 +356,15 @@ ExecSeqMarkPos(SeqScanState *node)
357356
void
358357
ExecSeqRestrPos(SeqScanState*node)
359358
{
360-
HeapScanDescscan;
359+
HeapScanDescscan=node->ss_currentScanDesc;
360+
361+
/*
362+
* Clear any reference to the previously returned tuple. This is
363+
* needed because the slot is simply pointing at scan->rs_cbuf, which
364+
* heap_restrpos will change; we'd have an internally inconsistent
365+
* slot if we didn't do this.
366+
*/
367+
ExecClearTuple(node->ss_ScanTupleSlot);
361368

362-
scan=node->ss_currentScanDesc;
363369
heap_restrpos(scan);
364370
}

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