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Commitcd70dd6

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Move the PredicateLockRelation() call from nodeSeqscan.c to heapam.c. It's
more consistent that way, since all the other PredicateLock* calls aremade in various heapam.c and index AM functions. The call in nodeSeqscan.cwas unnecessarily aggressive anyway, there's no need to try to lock therelation every time a tuple is fetched, it's enough to do it once.This has the user-visible effect that if a seq scan is initialized in theexecutor, but never executed, we now acquire the predicate lock on the heaprelation anyway. We could avoid that by taking the lock on the firstheap_getnext() call instead, but it doesn't seem worth the trouble giventhat it feels more natural to do it in heap_beginscan().Also, remove the retail PredicateLockTuple() calls from heap_getnext(). Ina seqscan, started with heap_begin(), we're holding a whole-relationpredicate lock on the heap so there's no need to lock the tuplesindividually.Kevin Grittner and me
1 parentd9fe63a commitcd70dd6

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3 files changed

+14
-14
lines changed

3 files changed

+14
-14
lines changed

‎src/backend/access/heap/heapam.c‎

Lines changed: 14 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -479,8 +479,6 @@ heapgettup(HeapScanDesc scan,
479479

480480
if (valid)
481481
{
482-
if (!scan->rs_relpredicatelocked)
483-
PredicateLockTuple(scan->rs_rd,tuple,snapshot);
484482
LockBuffer(scan->rs_cbuf,BUFFER_LOCK_UNLOCK);
485483
return;
486484
}
@@ -748,16 +746,12 @@ heapgettup_pagemode(HeapScanDesc scan,
748746
nkeys,key,valid);
749747
if (valid)
750748
{
751-
if (!scan->rs_relpredicatelocked)
752-
PredicateLockTuple(scan->rs_rd,tuple,scan->rs_snapshot);
753749
scan->rs_cindex=lineindex;
754750
return;
755751
}
756752
}
757753
else
758754
{
759-
if (!scan->rs_relpredicatelocked)
760-
PredicateLockTuple(scan->rs_rd,tuple,scan->rs_snapshot);
761755
scan->rs_cindex=lineindex;
762756
return;
763757
}
@@ -1228,13 +1222,26 @@ heap_beginscan_internal(Relation relation, Snapshot snapshot,
12281222
scan->rs_strategy=NULL;/* set in initscan */
12291223
scan->rs_allow_strat=allow_strat;
12301224
scan->rs_allow_sync=allow_sync;
1231-
scan->rs_relpredicatelocked= false;
12321225

12331226
/*
12341227
* we can use page-at-a-time mode if it's an MVCC-safe snapshot
12351228
*/
12361229
scan->rs_pageatatime=IsMVCCSnapshot(snapshot);
12371230

1231+
/*
1232+
* For a seqscan in a serializable transaction, acquire a predicate lock
1233+
* on the entire relation. This is required not only to lock all the
1234+
* matching tuples, but also to conflict with new insertions into the
1235+
* table. In an indexscan, we take page locks on the index pages covering
1236+
* the range specified in the scan qual, but in a heap scan there is
1237+
* nothing more fine-grained to lock. A bitmap scan is a different story,
1238+
* there we have already scanned the index and locked the index pages
1239+
* covering the predicate. But in that case we still have to lock any
1240+
* matching heap tuples.
1241+
*/
1242+
if (!is_bitmapscan)
1243+
PredicateLockRelation(relation,snapshot);
1244+
12381245
/* we only need to set this up once */
12391246
scan->rs_ctup.t_tableOid=RelationGetRelid(relation);
12401247

‎src/backend/executor/nodeSeqscan.c‎

Lines changed: 0 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -28,7 +28,6 @@
2828
#include"access/relscan.h"
2929
#include"executor/execdebug.h"
3030
#include"executor/nodeSeqscan.h"
31-
#include"storage/predicate.h"
3231

3332
staticvoidInitScanRelation(SeqScanState*node,EState*estate);
3433
staticTupleTableSlot*SeqNext(SeqScanState*node);
@@ -106,16 +105,11 @@ SeqRecheck(SeqScanState *node, TupleTableSlot *slot)
106105
*tuple.
107106
*We call the ExecScan() routine and pass it the appropriate
108107
*access method functions.
109-
*For serializable transactions, we first acquire a predicate
110-
*lock on the entire relation.
111108
* ----------------------------------------------------------------
112109
*/
113110
TupleTableSlot*
114111
ExecSeqScan(SeqScanState*node)
115112
{
116-
PredicateLockRelation(node->ss_currentRelation,
117-
node->ss_currentScanDesc->rs_snapshot);
118-
node->ss_currentScanDesc->rs_relpredicatelocked= true;
119113
returnExecScan((ScanState*)node,
120114
(ExecScanAccessMtd)SeqNext,
121115
(ExecScanRecheckMtd)SeqRecheck);

‎src/include/access/relscan.h‎

Lines changed: 0 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -35,7 +35,6 @@ typedef struct HeapScanDescData
3535
BlockNumberrs_startblock;/* block # to start at */
3636
BufferAccessStrategyrs_strategy;/* access strategy for reads */
3737
boolrs_syncscan;/* report location to syncscan logic? */
38-
boolrs_relpredicatelocked;/* predicate lock on relation exists */
3938

4039
/* scan current state */
4140
boolrs_inited;/* false = scan not init'd yet */

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