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Avoid having autovacuum workers wait for relation locks.

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Waiting for relation locks can lead to starvation - it pins down an
autovacuum worker for as long as the lock is held.  But if we're doing
an anti-wraparound vacuum, then we still wait; maintenance can no longer
be put off.

To assist with troubleshooting, if log_autovacuum_min_duration >= 0,
we log whenever an autovacuum or autoanalyze is skipped for this reason.

Per a gripe by Josh Berkus, and ensuing discussion.
This commit is contained in:
Robert Haas
2011-02-07 22:04:29 -05:00
parent 47082fa875
commit 32896c40ca
5 changed files with 61 additions and 15 deletions
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15
src/backend/commands/analyze.c
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@ -36,6 +36,7 @@
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/acl.h"
@ -148,7 +149,19 @@ analyze_rel(Oid relid, VacuumStmt *vacstmt,
* matter if we ever try to accumulate stats on dead tuples.) If the rel
* has been dropped since we last saw it, we don't need to process it.
*/
onerel = try_relation_open(relid, ShareUpdateExclusiveLock);
if (!(vacstmt->options & VACOPT_NOWAIT))
onerel = try_relation_open(relid, ShareUpdateExclusiveLock);
else if (ConditionalLockRelationOid(relid, ShareUpdateExclusiveLock))
onerel = try_relation_open(relid, NoLock);
else
{
onerel = NULL;
if (IsAutoVacuumWorkerProcess() && Log_autovacuum_min_duration >= 0)
ereport(LOG,
(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
errmsg("skipping analyze of \"%s\" --- lock not available",
vacstmt->relation->relname)));
}
if (!onerel)
return;