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Re: COMMIT NOWAIT Performance Option (patch)

From: "Simon Riggs" <simon(at)2ndquadrant(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-patches(at)postgresql(dot)org>,<pgsql-hackers(at)postgresql(dot)org>
Subject: Re: COMMIT NOWAIT Performance Option (patch)
Date: 2007-02-26 23:49:33
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackerspgsql-patches
On Mon, 2007-02-26 at 18:14 -0500, Tom Lane wrote:
> "Simon Riggs" <simon(at)2ndquadrant(dot)com> writes:
> > A prototype patch is posted to -patches, which is WORK IN PROGRESS.
> > [This patch matches discussion thread on -hackers.]
> What does this accomplish other than adding syntactic sugar over a
> feature that really doesn't work well anyway?  I don't see any point
> in encouraging people to use commit_delay in its present form.  If we
> had a portable solution for millisecond-or-so waits then maybe it would
> work ...

This patch doesn't intend to implement group commit. I've changed the
meaning of commit_delay, sorry if that confuses.

You and I discussed this in Toronto actually, IIRC. The best way to
describe this proposal is deferred fsync, so perhaps a different
parameter commit_fsync_delay would be more appropriate. 

Bruce has requested this feature many times from me, so I thought it
about time to publish.

The key point is that COMMIT NOWAIT doesn't wait for group commit to
return, it just doesn't wait at all - leaving someone else to flush WAL.
It's much better than fsync=off.

  Simon Riggs             

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