From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: [COMMITTERS] pgsql: Fix race condition in multixact code: it's possible |
Date: | 2005-10-28 17:48:42 |
Message-ID: | 200510281748.j9SHmgu18148@candle.pha.pa.us |
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Lists: | pgsql-committers pgsql-patches |
Does this need to be backpatched?
---------------------------------------------------------------------------
Tom Lane wrote:
> Log Message:
> -----------
> Fix race condition in multixact code: it's possible to try to read a
> multixact's starting offset before the offset has been stored into the
> SLRU file. A simple fix would be to hold the MultiXactGenLock until the
> offset has been stored, but that looks like a big concurrency hit. Instead
> rely on knowledge that unset offsets will be zero, and loop when we see
> a zero. This requires a little extra hacking to ensure that zero is never
> a valid value for the offset. Problem reported by Matteo Beccati, fix
> ideas from Martijn van Oosterhout, Alvaro Herrera, and Tom Lane.
>
> Modified Files:
> --------------
> pgsql/src/backend/access/transam:
> multixact.c (r1.9 -> r1.10)
> (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/transam/multixact.c.diff?r1=1.9&r2=1.10)
>
> ---------------------------(end of broadcast)---------------------------
> TIP 6: explain analyze is your friend
>
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
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