Received: from maia.hub.org (unknown [200.46.208.211]) by mail.postgresql.org (Postfix) with ESMTP id BAC2665ADAE for ; Tue, 16 Mar 2010 11:52:14 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.208.211]) (amavisd-maia, port 10024) with ESMTP id 07187-02-2 for ; Tue, 16 Mar 2010 14:51:54 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-px0-f197.google.com (mail-px0-f197.google.com [209.85.216.197]) by mail.postgresql.org (Postfix) with ESMTP id 08CC465AE95 for ; Tue, 16 Mar 2010 11:51:33 -0300 (ADT) Received: by pxi35 with SMTP id 35so2062026pxi.19 for ; Tue, 16 Mar 2010 07:51:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:from:date:x-google-sender-auth:message-id:subject:to:cc :content-type; bh=g6fQ2nKY95XZOOKY6i28uaQ74J7WpbcSRqzUUkl7bY0=; b=krEpx3cDzY8hx7MQVaNPLNc4wtYXfxKkYRfq/PGyJtTHl1MWNU/ovlDijJxsFNRLas K+WseLN1pJaTYboJCxAt+K94HJZQMFb906s99rVPsDJLUlzEi/+o1Yqhk9plCQ1a+qdt sAO+hXwh9YtmnDSYxG3bERLAuFqwH9jqKux04= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:from:date :x-google-sender-auth:message-id:subject:to:cc:content-type; b=YpSi/FCy0Lf6K+43IZGsr6kDbB01LqTTF5i9SpJa1ZuK8DntCgfQpZVxF17fUchhaV n0cjWTMQ94s14RSz2WEv/EqeiPBrC2E5J8+PmKAKslfOH9avtX6tL20otO24Kw1iRhE6 rNH76jgTFIf2ZQqAxKC6v4ef+D2oG6StaWJAU= MIME-Version: 1.0 Received: by 10.140.88.33 with SMTP id l33mr43296rvb.261.1268751091558; Tue, 16 Mar 2010 07:51:31 -0700 (PDT) In-Reply-To: References: <4B9F3302.4020900@2ndquadrant.com> From: Greg Stark Date: Tue, 16 Mar 2010 14:51:11 +0000 X-Google-Sender-Auth: 4f67ff516f85f7a9 Message-ID: <407d949e1003160751i43aaa472j4f90c4cf92a1e011@mail.gmail.com> Subject: Re: shared_buffers advice To: Pierre C Cc: Nikolas Everett , Greg Smith , Dave Crooke , Paul McGarry , pgsql-performance@postgresql.org Content-Type: text/plain; charset=ISO-8859-1 X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-2.478 tagged_above=-10 required=5 tests=AWL=0.121, BAYES_00=-2.599 X-Spam-Level: X-Archive-Number: 201003/168 X-Sequence-Number: 37993 On Tue, Mar 16, 2010 at 1:48 PM, Pierre C wrote: > Actually, I meant that in the case of a seq scan, PG will try to use just a > few buffers (a ring) in shared_buffers instead of thrashing the whole > buffers. But if there was actually a lot of free space in shared_buffers, do > the pages stay, or do they not ? They don't. The logic only kicks in if the table is expected to be > 1/4 of shared buffers though. -- greg