Received: from localhost (unknown [200.46.204.183]) by developer.postgresql.org (Postfix) with ESMTP id 561232E015B for ; Wed, 11 Jun 2008 21:54:22 -0300 (ADT) Received: from developer.postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 32170-05 for ; Wed, 11 Jun 2008 21:53:49 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from oxford.xeocode.com (87-127-95-198.no-dns-yet.enta.net [87.127.95.198]) by developer.postgresql.org (Postfix) with ESMTP id 5368D2E0082 for ; Wed, 11 Jun 2008 21:26:29 -0300 (ADT) Received: from localhost ([127.0.0.1] helo=oxford.xeocode.com) by oxford.xeocode.com with esmtp (Exim 4.69) (envelope-from ) id 1K6adl-00012u-OF; Thu, 12 Jun 2008 01:26:09 +0100 To: "Tom Lane" Cc: "Alvaro Herrera" , "Josh Berkus" , "Heikki Linnakangas" , , "Robert Treat" , "Peter Eisentraut" , "Greg Smith" , "Andreas Pflug" , "Decibel!" Subject: Re: Overhauling GUCS In-Reply-To: <11913.1213218315@sss.pgh.pa.us> (Tom Lane's message of "Wed\, 11 Jun 2008 17\:05\:15 -0400") User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.1 (gnu/linux) X-Draft-From: ("nnimap+mail01.enterprisedb.com:INBOX.hackers" 23305) References: <48409D1E.3070208@agliodbs.com> <200806061624.29105.xzilla@users.sourceforge.net> <200806100937.38124.josh@agliodbs.com> <200806100949.17918.josh@agliodbs.com> <21875.1213122184@sss.pgh.pa.us> <484F7613.5070202@enterprisedb.com> <484FFF06.9010307@agliodbs.com> <20080611163847.GN5352@alvh.no-ip.org> <11913.1213218315@sss.pgh.pa.us> From: Gregory Stark Organization: EnterpriseDB Date: Thu, 12 Jun 2008 01:26:09 +0100 Message-ID: <87od674hy6.fsf@oxford.xeocode.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200806/533 X-Sequence-Number: 119646 "Tom Lane" writes: > Alvaro Herrera writes: >> Josh Berkus wrote: >>> Ideally, of course, there would be no wal_buffers setting, and WAL >>> buffers would be allocated from shared_buffers pool on demand... > >> Same for pg_subtrans, pg_clog, etc (as previously discussed) > > I agree with that for pg_clog and friends, but I'm much more leery of > folding WAL into the same framework. Its access pattern is *totally* > unlike standard caches, so the argument that this would be good for > performance is resting on nothing but imagination. Also I'm concerned > about possible deadlocks, because WAL is customarily accessed while > holding one or more exclusive buffer locks. Well it may still be worthwhile stealing buffers from shared_buffers even if we set a special flag marking them as owned by WAL and out of bounds for the normal buffer manager. At least that way we could always steal more if we want or return some, as long as we're careful about when we do it. That would open the door to having these parameters be dynamically adjustable. That alone would be worthwhile even if we bypass all bells and whistles of the buffer manager. -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's RemoteDBA services!