Received: from maia.hub.org (maia-5.hub.org [200.46.204.29]) by mail.postgresql.org (Postfix) with ESMTP id 3F06C133655C for ; Mon, 4 Oct 2010 15:35:50 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.29]) (amavisd-maia, port 10024) with ESMTP id 84638-04 for ; Mon, 4 Oct 2010 18:35:43 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from midnight-anchovy.ambulatoryclam.net (unknown [18.141.0.210]) by mail.postgresql.org (Postfix) with ESMTP id EF72E133616B for ; Mon, 4 Oct 2010 15:35:42 -0300 (ADT) Received: by midnight-anchovy.ambulatoryclam.net (Postfix, from userid 1001) id BE5BB4AC2D; Mon, 4 Oct 2010 14:35:42 -0400 (EDT) Date: Mon, 4 Oct 2010 14:35:42 -0400 From: Dan Ports To: Robert Haas Cc: Hakan Kocaman , pgsql-hackers@postgresql.org Subject: Re: MIT benchmarks pgsql multicore (up to 48)performance Message-ID: <20101004183542.GB2690@csail.mit.edu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.107 tagged_above=-5 required=5 tests=BAYES_00=-1.9, RDNS_NONE=0.793 X-Spam-Level: X-Archive-Number: 201010/177 X-Sequence-Number: 171217 On Mon, Oct 04, 2010 at 01:13:36PM -0400, Robert Haas wrote: > I believe the "one of only 16 global mutexes" comment is referring to > NUM_LOCK_PARTITIONS (there's also NUM_BUFFER_PARTITIONS, but that > wouldn't be relevant for row and table-level locks). Yes -- my understanding is that they hit two lock-related problems: 1) LWLock contention caused by acquiring the same lock in compatible modes (e.g. multiple shared locks) 2) false contention caused by acquiring two locks that hashed to the same partition and the first was the worse problem. The lock-free structures helpe with both, so the impact of changing NUM_LOCK_PARTITIONS was less interesting. Dan -- Dan R. K. Ports MIT CSAIL http://drkp.net/