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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.
This commit is contained in:
Alvaro Herrera 2007-09-24 04:12:01 +00:00
parent 5853662630
commit 45cbdaa038
1 changed files with 49 additions and 10 deletions
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59
src/backend/postmaster/autovacuum.c
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@ -55,7 +55,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.60 2007/09/24 03:12:23 tgl Exp $
* $PostgreSQL: pgsql/src/backend/postmaster/autovacuum.c,v 1.61 2007/09/24 04:12:01 alvherre Exp $
*
*-------------------------------------------------------------------------
*/
@ -116,6 +116,9 @@ int autovacuum_vac_cost_limit;
int Log_autovacuum_min_duration = -1;
/* how long to keep pgstat data in the launcher, in milliseconds */
#define STATS_READ_DELAY 1000
/* Flags to tell if we are in an autovacuum process */
static bool am_autovacuum_launcher = false;
@ -291,6 +294,7 @@ static void avl_sighup_handler(SIGNAL_ARGS);
static void avl_sigusr1_handler(SIGNAL_ARGS);
static void avl_sigterm_handler(SIGNAL_ARGS);
static void avl_quickdie(SIGNAL_ARGS);
static void autovac_refresh_stats(void);
@ -488,7 +492,10 @@ AutoVacLauncherMain(int argc, char *argv[])
DatabaseListCxt = NULL;
DatabaseList = NULL;
/* Make sure pgstat also considers our stat data as gone */
/*
* Make sure pgstat also considers our stat data as gone. Note: we
* mustn't use autovac_refresh_stats here.
*/
pgstat_clear_snapshot();
/* Now we can allow interrupts again */
@ -836,7 +843,7 @@ rebuild_database_list(Oid newdb)
HTAB *dbhash;
/* use fresh stats */
pgstat_clear_snapshot();
autovac_refresh_stats();
newcxt = AllocSetContextCreate(AutovacMemCxt,
"AV dblist",
@ -1063,7 +1070,7 @@ do_start_worker(void)
oldcxt = MemoryContextSwitchTo(tmpcxt);
/* use fresh stats */
pgstat_clear_snapshot();
autovac_refresh_stats();
/* Get a list of databases */
dblist = get_database_list();
@ -1106,9 +1113,6 @@ do_start_worker(void)
avw_dbase *tmp = lfirst(cell);
Dlelem *elem;
/* Find pgstat entry if any */
tmp->adw_entry = pgstat_fetch_stat_dbentry(tmp->adw_datid);
/* Check to see if this one is at risk of wraparound */
if (TransactionIdPrecedes(tmp->adw_frozenxid, xidForceLimit))
{
@ -1121,9 +1125,12 @@ do_start_worker(void)
else if (for_xid_wrap)
continue; /* ignore not-at-risk DBs */
/* Find pgstat entry if any */
tmp->adw_entry = pgstat_fetch_stat_dbentry(tmp->adw_datid);
/*
* Otherwise, skip a database with no pgstat entry; it means it
* hasn't seen any activity.
* Skip a database with no pgstat entry; it means it hasn't seen any
* activity.
*/
if (!tmp->adw_entry)
continue;
@ -2258,7 +2265,7 @@ table_recheck_autovac(Oid relid)
PgStat_StatDBEntry *dbentry;
/* use fresh stats */
pgstat_clear_snapshot();
autovac_refresh_stats();
shared = pgstat_fetch_stat_dbentry(InvalidOid);
dbentry = pgstat_fetch_stat_dbentry(MyDatabaseId);
@ -2725,3 +2732,35 @@ AutoVacuumShmemInit(void)
else
Assert(found);
}
/*
* autovac_refresh_stats
* Refresh pgstats data for an autovacuum process
*
* Cause the next pgstats read operation to obtain fresh data, but throttle
* such refreshing in the autovacuum launcher. This is mostly to avoid
* rereading the pgstats files too many times in quick succession when there
* are many databases.
*
* Note: we avoid throttling in the autovac worker, as it would be
* counterproductive in the recheck logic.
*/
static void
autovac_refresh_stats(void)
{
if (IsAutoVacuumLauncherProcess())
{
static TimestampTz last_read = 0;
TimestampTz current_time;
current_time = GetCurrentTimestamp();
if (!TimestampDifferenceExceeds(last_read, current_time,
STATS_READ_DELAY))
return;
last_read = current_time;
}
pgstat_clear_snapshot();
}