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Re: COMMIT NOWAIT Performance Option

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: COMMIT NOWAIT Performance Option
Date: 2007-02-27 21:37:46
Message-ID: 200702272137.l1RLbkD08272@momjian.us (view raw, whole thread or download thread mbox)
Thread:
Lists: pgsql-hackers
Tom Lane wrote:
> "Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> > COMMIT NOWAIT can co-exist with the normal form of COMMIT and does not
> > threaten the consistency or robustness of other COMMIT modes. Read that
> > again and think about it, before we go further, please.
> 
> I read that, and thought about it, and don't think I believe it.  The
> problem is that there are more interconnections between different
> transactions than you're allowing for.  In particular you need to
> justify that the behavior is safe for non-transactional operations like
> btree page splits and pg_clog buffer page writes.  The idea that's
> particularly bothering me at the moment is that after a system crash,
> we might come back up in a state where a NOWAIT transaction appears
> committed when its updates didn't all get to disk.  "Database corrupt"
> is a situation that threatens all your transactions...
> 
> > New commit mode is available by explicit command, or as a default
> > setting that will be applied to all COMMITs, or both.
> 
> I dislike introducing new nonstandard syntax ("Oracle compatible" is not
> standard).  If we did this I'd vote for control via a GUC setting only;
> I think that is more useful anyway, as an application can be made to run
> with such a setting without invasive source code changes.

Agreed on the GUC-only.  I don't see many people using the per-COMMIT
setting without wanting it to be for many transactions in the session.

(And, YES, I am VERY excited we are getting this feature.)

-- 
  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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