Обсуждение: Re: [COMMITTERS] pgsql: Fix race condition in multixact code: it's possible

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)---------------------------
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  Bruce Momjian                        |  http://candle.pha.pa.us
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Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Does this need to be backpatched?

No.

            regards, tom lane