From: yamt@mwd.biglobe.ne.jp
To: Kevin.Grittner@wicourts.gov
Cc: pgsql-hackers@postgresql.org
Subject: Re: SSI bug?
Date: Sat, 12 Feb 2011 07:08:21 +0000 (UTC)
Message-ID: <20110212070822.46BE319D15D@mail.netbsd.org> (raw)
In-Reply-To: <4D5505E2020000250003A83C@gw.wicourts.gov>
References: <4D5505E2020000250003A83C@gw.wicourts.gov>
hi,
> YAMAMOTO Takashi <yamt@mwd.biglobe.ne.jp> wrote:
>
>> it seems that PredicateLockTupleRowVersionLink sometimes create
>> a loop of targets (it founds an existing 'newtarget' whose
>> nextVersionOfRow chain points to the 'oldtarget') and it later
>> causes CheckTargetForConflictsIn loop forever.
>
> Is this a hypothetical risk based on looking at the code, or have
> you seen this actually happen? Either way, could you provide more
> details? (A reproducible test case would be ideal.)
i have seen this actually happen. i've confirmed the creation of the loop
with the attached patch. it's easily reproducable with my application.
i can provide the full source code of my application if you want.
(but it isn't easy to run unless you are familiar with the recent
version of NetBSD)
i haven't found a smaller reproducible test case yet.
YAMAMOTO Takashi
>
> This being the newest part of the code, I'll grant that it is the
> most likely to have an unidentified bug; but given that the pointers
> are from one predicate lock target structure identified by a tuple
> ID to one identified by the tuple ID of the next version of the row,
> it isn't obvious to me how a cycle could develop.
>
> -Kevin
Attachments:a.diff (text/plain, 944B) downloaddiff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.cindex 722d0f8..3e1a3e2 100644--- a/src/backend/storage/lmgr/predicate.c+++ b/src/backend/storage/lmgr/predicate.c@@ -2350,7 +2350,25 @@ PredicateLockTupleRowVersionLink(const Relation relation,
newtarget->nextVersionOfRow = NULL;
}
else
+ {
Assert(newtarget->priorVersionOfRow == NULL);
+#if 0+ Assert(newtarget->nextVersionOfRow == NULL);+#endif+ if (newtarget->nextVersionOfRow != NULL) {+ PREDICATELOCKTARGET *t;++ elog(WARNING, "new %p has next %p\n",+ newtarget, newtarget->nextVersionOfRow);+ for (t = newtarget->nextVersionOfRow; t != NULL;+ t = t->nextVersionOfRow) {+ if (oldtarget != t) {+ elog(WARNING, "creating a loop new=%p old=%p\n",+ newtarget, oldtarget);+ }+ }+ }+ }
newtarget->priorVersionOfRow = oldtarget;
oldtarget->nextVersionOfRow = newtarget;
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To: pgsql-hackers@postgresql.org
Cc: yamt@mwd.biglobe.ne.jp, Kevin.Grittner@wicourts.gov
Subject: Re: SSI bug?
In-Reply-To: <20110212070822.46BE319D15D@mail.netbsd.org>
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