To: Simon Riggs <simon@2ndquadrant.com>
cc: cedric@dreamgnu.com, pgsql-performance@postgresql.org
Subject: Re: archive wal's failure and load increase. 
In-reply-to: <1159527513.2767.296.camel@holly> 
References: <451C2572.20800@dreamgnu.com> <1159527513.2767.296.camel@holly>
Comments: In-reply-to Simon Riggs <simon@2ndquadrant.com>
	message dated "Fri, 29 Sep 2006 11:58:33 +0100"
Date: Fri, 29 Sep 2006 10:29:22 -0400
Message-ID: <15270.1159540162@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Simon Riggs <simon@2ndquadrant.com> writes:
> We discussed putting PreallocXlogFiles() in bgwriter once before, but I
> think last time we discussed that idea it was rejected, IIRC.

We already do that: it's called a checkpoint.  If the rate of WAL
generation was more than checkpoint_segments per checkpoint_timeout,
then indeed there would be a problem with foreground processes having to
manufacture WAL segment files for themselves, but it would be a bursty
thing (ie, problem goes away after a checkpoint, then comes back).

It's a good thought but I don't think the theory holds water for
explaining Cedric's problem, unless there was *also* some effect
preventing checkpoints from completing ... which would be a much more
serious problem than the archiver failing.

			regards, tom lane