Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 699252E0216 for ; Thu, 20 Mar 2008 12:21:30 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 46214-01-3 for ; Thu, 20 Mar 2008 12:21:22 -0300 (ADT) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id C47252E0285 for ; Thu, 20 Mar 2008 12:20:58 -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 m2KFKd1a010280; Thu, 20 Mar 2008 11:20:39 -0400 (EDT) To: Bill Moran cc: "Albe Laurenz" , "Laurent Raufaste *EXTERN*" , pgsql-performance@postgresql.org Subject: Re: PG writes a lot to the disk In-reply-to: <20080320105833.c539476d.wmoran@collaborativefusion.com> References: <669dc9710803190418g45002e87k19cb742579c1eeac@mail.gmail.com> <669dc9710803200348x64122249jd2ac5924d78a6da0@mail.gmail.com> <20080320105833.c539476d.wmoran@collaborativefusion.com> Comments: In-reply-to Bill Moran message dated "Thu, 20 Mar 2008 10:58:33 -0400" Date: Thu, 20 Mar 2008 11:20:39 -0400 Message-ID: <10279.1206026439@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200803/409 X-Sequence-Number: 29363 Bill Moran writes: > However, the part I wanted to comment on (and got busy yesterday so > am only getting to it now) is that there's no guarantee that SELECT > isn't modifying rows. Another way that SELECT can cause disk writes is if it sets hint bits on recently-committed rows. However, if the tables aren't actively being modified any more, you'd expect that sort of activity to settle out pretty quickly. I concur with the temporary-file theory --- it's real hard to see how analyzing the tables would've fixed it otherwise. regards, tom lane