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Add a GUC variable "synchronize_seqscans" to allow clients to disable the new

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synchronized-scanning behavior, and make pg_dump disable sync scans so that
it will reliably preserve row ordering.  Per recent discussions.
This commit is contained in:
Tom Lane
2008-01-30 18:35:55 +00:00
parent 6dfa40d69f
commit 47df4f6688
5 changed files with 59 additions and 14 deletions
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11
src/backend/access/heap/heapam.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.248 2008/01/14 01:39:09 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.249 2008/01/30 18:35:55 tgl Exp $
*
*
* INTERFACE ROUTINES
@ -59,6 +59,10 @@
#include "utils/syscache.h"
/* GUC variable */
bool synchronize_seqscans = true;
static HeapScanDesc heap_beginscan_internal(Relation relation,
Snapshot snapshot,
int nkeys, ScanKey key,
@ -104,7 +108,8 @@ initscan(HeapScanDesc scan, ScanKey key)
* the thresholds for these features could be different, we make them the
* same so that there are only two behaviors to tune rather than four.
* (However, some callers need to be able to disable one or both of
* these behaviors, independently of the size of the table.)
* these behaviors, independently of the size of the table; also there
* is a GUC variable that can disable synchronized scanning.)
*
* During a rescan, don't make a new strategy object if we don't have to.
*/
@ -129,7 +134,7 @@ initscan(HeapScanDesc scan, ScanKey key)
scan->rs_strategy = NULL;
}
if (allow_sync)
if (allow_sync && synchronize_seqscans)
{
scan->rs_syncscan = true;
scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks);