Thread: Re: [COMMITTERS] pgsql: Fix race condition in multixact code: it's possible
Re: [COMMITTERS] pgsql: Fix race condition in multixact code: it's possible
From
Bruce Momjian
Date:
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@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073
Re: [COMMITTERS] pgsql: Fix race condition in multixact code: it's possible to try to
From
Tom Lane
Date:
Bruce Momjian <pgman@candle.pha.pa.us> writes: > Does this need to be backpatched? No. regards, tom lane