X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (av.hub.org [200.46.204.144]) by postgresql.org (Postfix) with ESMTP id D62EA9DC9A0 for ; Tue, 20 Dec 2005 12:17:05 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 09686-07 for ; Tue, 20 Dec 2005 12:17:04 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey- Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by postgresql.org (Postfix) with ESMTP id EE3329DC862 for ; Tue, 20 Dec 2005 12:17:02 -0400 (AST) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.1/8.13.1) with ESMTP id jBKGGqwI000126; Tue, 20 Dec 2005 11:16:52 -0500 (EST) To: Greg Stark cc: Markus Schaber , PostgreSQL Performance List Subject: Re: Read only transactions - Commit or Rollback In-reply-to: <87irtjah9m.fsf@stark.xeocode.com> References: <16F953410A0F1346848DCB476A989CFE01D6AF@swtexchange2.technology.de> <43A7F303.8040804@logix-tt.com> <87mziwj6na.fsf@gate450.dyndns.org> <43A7F9B9.3010906@logix-tt.com> <29672.1135093688@sss.pgh.pa.us> <87irtjah9m.fsf@stark.xeocode.com> Comments: In-reply-to Greg Stark message dated "20 Dec 2005 11:02:29 -0500" Date: Tue, 20 Dec 2005 11:16:52 -0500 Message-ID: <125.1135095412@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, score=0.022 required=5 tests=[AWL=0.022] X-Spam-Score: 0.022 X-Spam-Level: X-Archive-Number: 200512/500 X-Sequence-Number: 16321 Greg Stark writes: > Tom Lane writes: >> That surprises me too --- can you provide details on the test case so >> other people can reproduce it? AFAIR the only performance difference >> between SERIALIZABLE and READ COMMITTED is the frequency with which >> transaction status snapshots are taken; your report suggests you were >> spending 30% of the time in GetSnapshotData, which is a lot higher than >> I've ever seen in a profile. > Perhaps it reduced the amount of i/o concurrent vacuums were doing? Can't see how it would do that. regards, tom lane