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Commit45cbdaa

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Avoid having autovacuum read pgstats data too many times in quick succession.
This is problematic for the autovac launcher when there are many databases,so we keep data for a full second before reading it again.
1 parent5853662 commit45cbdaa

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1 file changed

+49
-10
lines changed

1 file changed

+49
-10
lines changed

‎src/backend/postmaster/autovacuum.c

Lines changed: 49 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -55,7 +55,7 @@
5555
*
5656
*
5757
* IDENTIFICATION
58-
* $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.60 2007/09/2403:12:23 tgl Exp $
58+
* $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.61 2007/09/2404:12:01 alvherre Exp $
5959
*
6060
*-------------------------------------------------------------------------
6161
*/
@@ -116,6 +116,9 @@ intautovacuum_vac_cost_limit;
116116

117117
intLog_autovacuum_min_duration=-1;
118118

119+
/* how long to keep pgstat data in the launcher, in milliseconds */
120+
#defineSTATS_READ_DELAY 1000
121+
119122

120123
/* Flags to tell if we are in an autovacuum process */
121124
staticboolam_autovacuum_launcher= false;
@@ -291,6 +294,7 @@ static void avl_sighup_handler(SIGNAL_ARGS);
291294
staticvoidavl_sigusr1_handler(SIGNAL_ARGS);
292295
staticvoidavl_sigterm_handler(SIGNAL_ARGS);
293296
staticvoidavl_quickdie(SIGNAL_ARGS);
297+
staticvoidautovac_refresh_stats(void);
294298

295299

296300

@@ -488,7 +492,10 @@ AutoVacLauncherMain(int argc, char *argv[])
488492
DatabaseListCxt=NULL;
489493
DatabaseList=NULL;
490494

491-
/* Make sure pgstat also considers our stat data as gone */
495+
/*
496+
* Make sure pgstat also considers our stat data as gone. Note: we
497+
* mustn't use autovac_refresh_stats here.
498+
*/
492499
pgstat_clear_snapshot();
493500

494501
/* Now we can allow interrupts again */
@@ -836,7 +843,7 @@ rebuild_database_list(Oid newdb)
836843
HTAB*dbhash;
837844

838845
/* use fresh stats */
839-
pgstat_clear_snapshot();
846+
autovac_refresh_stats();
840847

841848
newcxt=AllocSetContextCreate(AutovacMemCxt,
842849
"AV dblist",
@@ -1063,7 +1070,7 @@ do_start_worker(void)
10631070
oldcxt=MemoryContextSwitchTo(tmpcxt);
10641071

10651072
/* use fresh stats */
1066-
pgstat_clear_snapshot();
1073+
autovac_refresh_stats();
10671074

10681075
/* Get a list of databases */
10691076
dblist=get_database_list();
@@ -1106,9 +1113,6 @@ do_start_worker(void)
11061113
avw_dbase*tmp=lfirst(cell);
11071114
Dlelem*elem;
11081115

1109-
/* Find pgstat entry if any */
1110-
tmp->adw_entry=pgstat_fetch_stat_dbentry(tmp->adw_datid);
1111-
11121116
/* Check to see if this one is at risk of wraparound */
11131117
if (TransactionIdPrecedes(tmp->adw_frozenxid,xidForceLimit))
11141118
{
@@ -1121,9 +1125,12 @@ do_start_worker(void)
11211125
elseif (for_xid_wrap)
11221126
continue;/* ignore not-at-risk DBs */
11231127

1128+
/* Find pgstat entry if any */
1129+
tmp->adw_entry=pgstat_fetch_stat_dbentry(tmp->adw_datid);
1130+
11241131
/*
1125-
*Otherwise, skipa database with no pgstat entry; it means it
1126-
*hasn't seen anyactivity.
1132+
*Skipa database with no pgstat entry; it means it hasn't seen any
1133+
* activity.
11271134
*/
11281135
if (!tmp->adw_entry)
11291136
continue;
@@ -2258,7 +2265,7 @@ table_recheck_autovac(Oid relid)
22582265
PgStat_StatDBEntry*dbentry;
22592266

22602267
/* use fresh stats */
2261-
pgstat_clear_snapshot();
2268+
autovac_refresh_stats();
22622269

22632270
shared=pgstat_fetch_stat_dbentry(InvalidOid);
22642271
dbentry=pgstat_fetch_stat_dbentry(MyDatabaseId);
@@ -2725,3 +2732,35 @@ AutoVacuumShmemInit(void)
27252732
else
27262733
Assert(found);
27272734
}
2735+
2736+
/*
2737+
* autovac_refresh_stats
2738+
* Refresh pgstats data for an autovacuum process
2739+
*
2740+
* Cause the next pgstats read operation to obtain fresh data, but throttle
2741+
* such refreshing in the autovacuum launcher. This is mostly to avoid
2742+
* rereading the pgstats files too many times in quick succession when there
2743+
* are many databases.
2744+
*
2745+
* Note: we avoid throttling in the autovac worker, as it would be
2746+
* counterproductive in the recheck logic.
2747+
*/
2748+
staticvoid
2749+
autovac_refresh_stats(void)
2750+
{
2751+
if (IsAutoVacuumLauncherProcess())
2752+
{
2753+
staticTimestampTzlast_read=0;
2754+
TimestampTzcurrent_time;
2755+
2756+
current_time=GetCurrentTimestamp();
2757+
2758+
if (!TimestampDifferenceExceeds(last_read,current_time,
2759+
STATS_READ_DELAY))
2760+
return;
2761+
2762+
last_read=current_time;
2763+
}
2764+
2765+
pgstat_clear_snapshot();
2766+
}

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