From: Dan Ports <drkp@csail.mit.edu>
To: pgsql-hackers@postgresql.org
Cc: YAMAMOTO Takashi <yamt@mwd.biglobe.ne.jp>
Cc: Kevin Grittner <Kevin.Grittner@wicourts.gov>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Subject: Re: SSI bug?
Date: Sun, 3 Apr 2011 02:16:44 -0400
Message-ID: <20110403061644.GS81592@csail.mit.edu> (raw)
In-Reply-To: <4D943BEC020000250003BFDA@gw.wicourts.gov>
References: <4D8F54E6020000250003BD16@gw.wicourts.gov>
<4D8F54E6020000250003BD16@gw.wicourts.gov>
<20110328031616.CDAA719CEDF@mail.netbsd.org>
<4D943BEC020000250003BFDA@gw.wicourts.gov>
I think I see what is going on now. We are sometimes failing to set the
commitSeqNo correctly on the lock. In particular, if a lock assigned to
OldCommittedSxact is marked with InvalidSerCommitNo, it will never be
cleared.
The attached patch corrects this:
TransferPredicateLocksToNewTarget should initialize a new lock
entry's commitSeqNo to that of the old one being transferred, or take
the minimum commitSeqNo if it is merging two lock entries.
Also, CreatePredicateLock should initialize commitSeqNo for to
InvalidSerCommitSeqNo instead of to 0. (I don't think using 0 would
actually affect anything, but we should be consistent.)
I also added a couple of assertions I used to track this down: a
lock's commitSeqNo should never be zero, and it should be
InvalidSerCommitSeqNo if and only if the lock is not held by
OldCommittedSxact.
Takashi, does this patch fix your problem with leaked SIReadLocks?
Dan
--
Dan R. K. Ports MIT CSAIL http://drkp.net/Attachments:patch-commitseqno.diff (text/x-diff, 2.3K) downloaddiff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.cindex f6e49fe..d166da3 100644--- a/src/backend/storage/lmgr/predicate.c+++ b/src/backend/storage/lmgr/predicate.c@@ -2067,7 +2067,7 @@ CreatePredicateLock(const PREDICATELOCKTARGETTAG *targettag,
SHMQueueInsertBefore(&(target->predicateLocks), &(lock->targetLink));
SHMQueueInsertBefore(&(sxact->predicateLocks),
&(lock->xactLink));
- lock->commitSeqNo = 0;+ lock->commitSeqNo = InvalidSerCommitSeqNo;
}
LWLockRelease(partitionLock);
@@ -2500,6 +2500,7 @@ TransferPredicateLocksToNewTarget(const PREDICATELOCKTARGETTAG oldtargettag,
SHM_QUEUE *predlocktargetlink;
PREDICATELOCK *nextpredlock;
PREDICATELOCK *newpredlock;
+ SerCommitSeqNo oldCommitSeqNo = oldpredlock->commitSeqNo;
predlocktargetlink = &(oldpredlock->targetLink);
nextpredlock = (PREDICATELOCK *)
@@ -2544,8 +2545,17 @@ TransferPredicateLocksToNewTarget(const PREDICATELOCKTARGETTAG oldtargettag,
&(newpredlock->targetLink));
SHMQueueInsertBefore(&(newpredlocktag.myXact->predicateLocks),
&(newpredlock->xactLink));
- newpredlock->commitSeqNo = InvalidSerCommitSeqNo;+ newpredlock->commitSeqNo = oldCommitSeqNo;
}
+ else+ {+ if (newpredlock->commitSeqNo < oldCommitSeqNo)+ newpredlock->commitSeqNo = oldCommitSeqNo;+ }+ + Assert(newpredlock->commitSeqNo != 0);+ Assert((newpredlock->commitSeqNo == InvalidSerCommitSeqNo)+ || (newpredlock->tag.myXact == OldCommittedSxact));
oldpredlock = nextpredlock;
}
@@ -3130,6 +3140,8 @@ ClearOldPredicateLocks(void)
offsetof(PREDICATELOCK, xactLink));
LWLockAcquire(SerializableXactHashLock, LW_SHARED);
+ Assert(predlock->commitSeqNo != 0);+ Assert(predlock->commitSeqNo != InvalidSerCommitSeqNo);
canDoPartialCleanup = (predlock->commitSeqNo <= PredXact->CanPartialClearThrough);
LWLockRelease(SerializableXactHashLock);
@@ -3254,6 +3266,8 @@ ReleaseOneSerializableXact(SERIALIZABLEXACT *sxact, bool partial,
errhint("You might need to increase max_pred_locks_per_transaction.")));
if (found)
{
+ Assert(predlock->commitSeqNo != 0);+ Assert(predlock->commitSeqNo != InvalidSerCommitSeqNo);
if (predlock->commitSeqNo < sxact->commitSeqNo)
predlock->commitSeqNo = sxact->commitSeqNo;
}
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To: pgsql-hackers@postgresql.org
Cc: drkp@csail.mit.edu, yamt@mwd.biglobe.ne.jp, Kevin.Grittner@wicourts.gov, heikki.linnakangas@enterprisedb.com
Subject: Re: SSI bug?
In-Reply-To: <20110403061644.GS81592@csail.mit.edu>
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