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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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39
src/backend/commands/vacuum.c
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@@ -61,7 +61,7 @@ static BufferAccessStrategy vac_strategy;
/* non-export function prototypes */
static List *get_rel_oids(Oid relid, const RangeVar *vacrel);
static void vac_truncate_clog(TransactionId frozenXID);
static void vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast,
static bool vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast,
bool for_wraparound, bool *scanned_all);
@@ -226,8 +226,11 @@ vacuum(VacuumStmt *vacstmt, Oid relid, bool do_toast,
bool scanned_all = false;
if (vacstmt->options & VACOPT_VACUUM)
vacuum_rel(relid, vacstmt, do_toast, for_wraparound,
&scanned_all);
{
if (!vacuum_rel(relid, vacstmt, do_toast, for_wraparound,
&scanned_all))
continue;
}
if (vacstmt->options & VACOPT_ANALYZE)
{
@@ -764,7 +767,7 @@ vac_truncate_clog(TransactionId frozenXID)
*
* At entry and exit, we are not inside a transaction.
*/
static void
static bool
vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
bool *scanned_all)
{
@@ -835,14 +838,29 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
*
* There's a race condition here: the rel may have gone away since the
* last time we saw it. If so, we don't need to vacuum it.
*
* If we've been asked not to wait for the relation lock, acquire it
* first in non-blocking mode, before calling try_relation_open().
*/
onerel = try_relation_open(relid, lmode);
if (!(vacstmt->options & VACOPT_NOWAIT))
onerel = try_relation_open(relid, lmode);
else if (ConditionalLockRelationOid(relid, lmode))
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 vacuum of \"%s\" --- lock not available",
vacstmt->relation->relname)));
}
if (!onerel)
{
PopActiveSnapshot();
CommitTransactionCommand();
return;
return false;
}
/*
@@ -873,7 +891,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
relation_close(onerel, lmode);
PopActiveSnapshot();
CommitTransactionCommand();
return;
return false;
}
/*
@@ -890,7 +908,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
relation_close(onerel, lmode);
PopActiveSnapshot();
CommitTransactionCommand();
return;
return false;
}
/*
@@ -905,7 +923,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
relation_close(onerel, lmode);
PopActiveSnapshot();
CommitTransactionCommand();
return;
return false;
}
/*
@@ -989,6 +1007,9 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
* Now release the session-level lock on the master table.
*/
UnlockRelationIdForSession(&onerelid, lmode);
/* Report that we really did it. */
return true;
}