Re: Free WAL caches on switching segments

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>, daveg <daveg(at)sonic(dot)net>, ITAGAKI Takahiro <itagaki(dot)takahiro(at)lab(dot)ntt(dot)co(dot)jp>, pgsql-patches(at)postgresql(dot)org
Subject: Re: Free WAL caches on switching segments
Date: 2006-03-02 19:26:42
Message-ID: 200603021926.k22JQgb19347@candle.pha.pa.us
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Tom Lane wrote:
> Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> writes:
> > Thinking about this, presumably any write intensive, multi-user
> > benchmark would seem to be suitable, so would something like OSDL's
> > DBT-2 actually be better to try?
>
> I'm certainly not wedded to pgbench, give it a try.
>
> BTW, I forgot to mention that it would be useful to try different
> wal_sync_methods along with this. The reason why it seems unlikely
> the patch is useful on Linux is that the sync methods that use O_DIRECT
> probably dominate using the patch anyway. There may or may not be
> a similar dependence on sync method on other kernels ...

I am thinking the only way to test this would be to do one heavy update
session to generate a lot of WAL traffic, and another session that is
doing a sequential scan on a table that fills most of the cache. It
isn't an easy test to make, which was why I was thinking we just add the
patch, but the community disagrees.

--
Bruce Momjian http://candle.pha.pa.us
SRA OSS, Inc. http://www.sraoss.com

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

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