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Re: [HACKERS] CIC and deadlocks

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>, pgsql-patches(at)postgresql(dot)org
Subject: Re: [HACKERS] CIC and deadlocks
Date: 2007-04-27 01:05:51
Message-ID: 200704270105.l3R15pT20828@momjian.us (view raw or flat)
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Pavan Deolasee wrote:
> On 4/11/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> 
> >
> > [ itch... ]  The problem is with time-extended execution of
> > GetSnapshotData; what happens if the other guy lost the CPU for a good
> > long time while in the middle of GetSnapshotData?  He might set his
> > xmin based on info you saw as long gone.
> >
> > You might be correct that it's safe, but the argument would have to
> > hinge on the OldestXmin process being unable to commit because of
> > someone holding shared ProcArrayLock; a point you are definitely not
> > making above.  (Study the comments in GetSnapshotData for awhile,
> > also those in xact.c's commit-related code.)
> >
> >
> My argument was based on what you said above, but I obviously did not
> state it well :)
> 
> Anyways, I think its better to be safe and we agree that its not such a
> bad thing to take exclusive lock on procarray because CIC is not something
> that happens very often. Attached is a revised patch which takes exclusive
> lock on the procarray, rest remaining the same.
> 
> Thanks,
> Pavan
> 
> -- 
> 
> EnterpriseDB     http://www.enterprisedb.com

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-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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