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Move the PredicateLockRelation() call from nodeSeqscan.c to heapam.c. It's

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more consistent that way, since all the other PredicateLock* calls are
made in various heapam.c and index AM functions. The call in nodeSeqscan.c
was unnecessarily aggressive anyway, there's no need to try to lock the
relation 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 the
executor, but never executed, we now acquire the predicate lock on the heap
relation anyway. We could avoid that by taking the lock on the first
heap_getnext() call instead, but it doesn't seem worth the trouble given
that it feels more natural to do it in heap_beginscan().

Also, remove the retail PredicateLockTuple() calls from heap_getnext(). In
a seqscan, started with heap_begin(), we're holding a whole-relation
predicate lock on the heap so there's no need to lock the tuples
individually.

Kevin Grittner and me
This commit is contained in:
Heikki Linnakangas
2011-06-29 21:43:53 +03:00
parent d9fe63acb0
commit cd70dd6bef
3 changed files with 14 additions and 14 deletions
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6
src/backend/executor/nodeSeqscan.c
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@ -28,7 +28,6 @@
#include "access/relscan.h"
#include "executor/execdebug.h"
#include "executor/nodeSeqscan.h"
#include "storage/predicate.h"
static void InitScanRelation(SeqScanState *node, EState *estate);
static TupleTableSlot *SeqNext(SeqScanState *node);
@ -106,16 +105,11 @@ SeqRecheck(SeqScanState *node, TupleTableSlot *slot)
* tuple.
* We call the ExecScan() routine and pass it the appropriate
* access method functions.
* For serializable transactions, we first acquire a predicate
* lock on the entire relation.
* ----------------------------------------------------------------
*/
TupleTableSlot *
ExecSeqScan(SeqScanState *node)
{
PredicateLockRelation(node->ss_currentRelation,
node->ss_currentScanDesc->rs_snapshot);
node->ss_currentScanDesc->rs_relpredicatelocked = true;
return ExecScan((ScanState *) node,
(ExecScanAccessMtd) SeqNext,
(ExecScanRecheckMtd) SeqRecheck);