Received: from localhost (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id B0ACC6337D7 for ; Sat, 14 Mar 2009 13:02:35 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 35816-03 for ; Sat, 14 Mar 2009 13:02:29 -0300 (ADT) Received: from mx2.hub.org (mx2.hub.org [200.46.204.254]) by mail.postgresql.org (Postfix) with ESMTP id 13B2B6357D9 for ; Sat, 14 Mar 2009 12:54:08 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by mx2.hub.org (Postfix) with ESMTP id 6694C1E83950 for ; Sat, 14 Mar 2009 12:54:06 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.14.2/8.14.2) with ESMTP id n2EFq58b004862; Sat, 14 Mar 2009 11:52:05 -0400 (EDT) To: Robert Haas cc: Gregory Stark , Alan Stange , "Jignesh K. Shah" , Greg Smith , "pgsql-performance@postgresql.org" Subject: Re: 8.4 Performance improvements: was Re: Proposal of tunable fix for scalability of 8.4 In-reply-to: <603c8f070903131937t1c33fa97k29e7d8d07fa2e83@mail.gmail.com> References: <49B922C0.6050700@sun.com> <49BA5537.8060002@sun.com> <87prgl4jbh.fsf@oxford.xeocode.com> <49BA79A4.9030208@rentec.com> <12431.1236965004@sss.pgh.pa.us> <87d4ck50h1.fsf@oxford.xeocode.com> <26666.1236996376@sss.pgh.pa.us> <603c8f070903131937t1c33fa97k29e7d8d07fa2e83@mail.gmail.com> Comments: In-reply-to Robert Haas message dated "Fri, 13 Mar 2009 22:37:37 -0400" Date: Sat, 14 Mar 2009 11:52:05 -0400 Message-ID: <4861.1237045925@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0.015 tagged_above=0 required=5 tests=AWL=0.015 X-Spam-Level: X-Archive-Number: 200903/188 X-Sequence-Number: 33110 Robert Haas writes: > On Fri, Mar 13, 2009 at 10:06 PM, Tom Lane wrote: >> I assume you meant effective_io_concurrency.  We'd still need a special >> case because the default is currently hard-wired at 1, not 0, if >> configure thinks the function exists. > I think 1 should mean no prefetching, rather than 0. No, 1 means "prefetch a single block ahead". It doesn't involve I/O concurrency in the sense of multiple I/O requests being processed at once; what it does give you is CPU vs I/O concurrency. 0 shuts that down and returns the system to pre-8.4 behavior. regards, tom lane