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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
View File

@ -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);

12
src/backend/utils/misc/guc.c
View File

@ -10,7 +10,7 @@
* Written by Peter Eisentraut <peter_e@gmx.net>.
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.431 2008/01/27 19:12:28 tgl Exp $
* $PostgreSQL: pgsql/src/backend/utils/misc/guc.c,v 1.432 2008/01/30 18:35:55 tgl Exp $
*
*--------------------------------------------------------------------
*/
@ -110,6 +110,7 @@ extern int CommitDelay;
extern int CommitSiblings;
extern char *default_tablespace;
extern char *temp_tablespaces;
extern bool synchronize_seqscans;
extern bool fullPageWrites;
#ifdef TRACE_SORT
@ -1052,6 +1053,15 @@ static struct config_bool ConfigureNamesBool[] =
false, NULL, NULL
},
{
{"synchronize_seqscans", PGC_USERSET, COMPAT_OPTIONS_PREVIOUS,
gettext_noop("Enable synchronized sequential scans."),
NULL
},
&synchronize_seqscans,
true, NULL, NULL
},
{
{"archive_mode", PGC_POSTMASTER, WAL_SETTINGS,
gettext_noop("Allows archiving of WAL files using archive_command."),

3
src/backend/utils/misc/postgresql.conf.sample
View File

@ -476,9 +476,10 @@
#backslash_quote = safe_encoding # on, off, or safe_encoding
#default_with_oids = off
#escape_string_warning = on
#standard_conforming_strings = off
#regex_flavor = advanced # advanced, extended, or basic
#sql_inheritance = on
#standard_conforming_strings = off
#synchronize_seqscans = on
# - Other Platforms and Clients -

23
src/bin/pg_dump/pg_dump.c
View File

@ -12,7 +12,7 @@
* by PostgreSQL
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.481 2008/01/01 19:45:55 momjian Exp $
* $PostgreSQL: pgsql/src/bin/pg_dump/pg_dump.c,v 1.482 2008/01/30 18:35:55 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -552,6 +552,20 @@ main(int argc, char **argv)
/* Set the datestyle to ISO to ensure the dump's portability */
do_sql_command(g_conn, "SET DATESTYLE = ISO");
/*
* If supported, set extra_float_digits so that we can dump float data
* exactly (given correctly implemented float I/O code, anyway)
*/
if (g_fout->remoteVersion >= 70400)
do_sql_command(g_conn, "SET extra_float_digits TO 2");
/*
* If synchronized scanning is supported, disable it, to prevent
* unpredictable changes in row ordering across a dump and reload.
*/
if (g_fout->remoteVersion >= 80300)
do_sql_command(g_conn, "SET synchronize_seqscans TO off");
/*
* Start serializable transaction to dump consistent data.
*/
@ -567,13 +581,6 @@ main(int argc, char **argv)
else
username_subquery = "SELECT usename FROM pg_user WHERE usesysid =";
/*
* If supported, set extra_float_digits so that we can dump float data
* exactly (given correctly implemented float I/O code, anyway)
*/
if (g_fout->remoteVersion >= 70400)
do_sql_command(g_conn, "SET extra_float_digits TO 2");
/* Find the last built-in OID, if needed */
if (g_fout->remoteVersion < 70300)
{