To: Dave Page <dpage@pgadmin.org>
cc: Robert Haas <robertmhaas@gmail.com>, Bruce Momjian <bruce@momjian.us>,
	Dimitri Fontaine <dfontaine@hi-media.com>, Josh Berkus <josh@agliodbs.com>,
	postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: PostgreSQL as a local in-memory cache 
In-reply-to: <AANLkTimxDE1PRSaIhLFqRfaXoG7zxbDNH9mQO4aK4Kkt@mail.gmail.com> 
References: <24597.1276803510@sss.pgh.pa.us>
	<201006231937.o5NJbKp05127@momjian.us>
	<AANLkTikTFG8-4sfJsQ16Fdu1TzZOh_zUtb-QuBPuo9jF@mail.gmail.com>
	<AANLkTimxDE1PRSaIhLFqRfaXoG7zxbDNH9mQO4aK4Kkt@mail.gmail.com>
Comments: In-reply-to Dave Page <dpage@pgadmin.org>
	message dated "Wed, 23 Jun 2010 21:27:38 +0100"
Date: Wed, 23 Jun 2010 16:43:06 -0400
Message-ID: <27712.1277325786@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

Dave Page <dpage@pgadmin.org> writes:
> On Wed, Jun 23, 2010 at 9:25 PM, Robert Haas <robertmhaas@gmail.com> wrote:
>> I don't think we need a system-wide setting for that. 狢 believe that
>> the unlogged tables I'm working on will handle that case.

> Aren't they going to be truncated at startup? If the entire system is
> running without WAL, we would only need to do that in case of an
> unclean shutdown wouldn't we?

The problem with a system-wide no-WAL setting is it means you can't
trust the system catalogs after a crash.  Which means you are forced to
use initdb to recover from any crash, in return for not a lot of savings
(for typical usages where there's not really much churn in the
catalogs).  I tend to agree with Robert that a way to not log content
updates for individual user tables is likely to be much more useful in
practice.

			regards, tom lane