From: Dimitri Fontaine <dfontaine@hi-media.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Dave Page <dpage@pgadmin.org>, Robert Haas <robertmhaas@gmail.com>,
	Bruce Momjian <bruce@momjian.us>, Josh Berkus <josh@agliodbs.com>,
	postgres performance list <pgsql-performance@postgresql.org>
Subject: Re: PostgreSQL as a local in-memory cache
Organization: Hi-Media
References: <24597.1276803510@sss.pgh.pa.us>
	<201006231937.o5NJbKp05127@momjian.us>
	<AANLkTikTFG8-4sfJsQ16Fdu1TzZOh_zUtb-QuBPuo9jF@mail.gmail.com>
	<AANLkTimxDE1PRSaIhLFqRfaXoG7zxbDNH9mQO4aK4Kkt@mail.gmail.com>
	<27712.1277325786@sss.pgh.pa.us>
User-Mail-Address: dfontaine@hi-media.com
Date: Thu, 24 Jun 2010 10:25:23 +0200
In-Reply-To: <27712.1277325786@sss.pgh.pa.us> (Tom Lane's message of "Wed, 23
	Jun 2010 16:43:06 -0400")
Message-ID: <87sk4cu9ak.fsf@hi-media-techno.com>
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Tom Lane <tgl@sss.pgh.pa.us> writes:
> 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).=20

What about having a "catalog only" WAL setting, userset=C2=A0?

I'm not yet clear on the point but it well seems that the per
transaction WAL setting is impossible because of catalogs (meaning
mainly DDL support), but I can see us enforcing durability and crash
safety there.

That would probably mean that setting WAL level this low yet doing any
kind of DDL would need to be either an ERROR, or better yet, a WARNING
telling that the WAL level can not be that low so has been raised by the
system.

Regards,
--=20
dim