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Teach heapam code to know the difference between a real seqscan and the

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pseudo HeapScanDesc created for a bitmap heap scan.  This avoids some useless
overhead during a bitmap scan startup, in particular invoking the syncscan
code.  (We might someday want to do that, but right now it's merely useless
contention for shared memory, to say nothing of possibly pushing useful
entries out of syncscan's small LRU list.)  This also allows elimination of
ugly pgstat_discount_heap_scan() kluge.
This commit is contained in:
Tom Lane
2007-06-09 18:49:55 +00:00
parent 7063c46fc1
commit 85d72f0516
5 changed files with 48 additions and 34 deletions
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23
src/backend/executor/nodeBitmapHeapscan.c
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@ -21,7 +21,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.17 2007/05/27 03:50:39 tgl Exp $
* $PostgreSQL: pgsql/src/backend/executor/nodeBitmapHeapscan.c,v 1.18 2007/06/09 18:49:55 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -388,9 +388,6 @@ ExecBitmapHeapReScan(BitmapHeapScanState *node, ExprContext *exprCtxt)
/* rescan to release any page pin */
heap_rescan(node->ss.ss_currentScanDesc, NULL);
/* undo bogus "seq scan" count (see notes in ExecInitBitmapHeapScan) */
pgstat_discount_heap_scan(node->ss.ss_currentScanDesc->rs_rd);
if (node->tbm)
tbm_free(node->tbm);
node->tbm = NULL;
@ -522,20 +519,12 @@ ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
/*
* Even though we aren't going to do a conventional seqscan, it is useful
* to create a HeapScanDesc --- this checks the relation size and sets up
* statistical infrastructure for us.
* to create a HeapScanDesc --- most of the fields in it are usable.
*/
scanstate->ss.ss_currentScanDesc = heap_beginscan(currentRelation,
estate->es_snapshot,
0,
NULL);
/*
* One problem is that heap_beginscan counts a "sequential scan" start,
* when we actually aren't doing any such thing. Reverse out the added
* scan count. (Eventually we may want to count bitmap scans separately.)
*/
pgstat_discount_heap_scan(scanstate->ss.ss_currentScanDesc->rs_rd);
scanstate->ss.ss_currentScanDesc = heap_beginscan_bm(currentRelation,
estate->es_snapshot,
0,
NULL);
/*
* get the scan type from the relation descriptor.