X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (unknown [200.46.204.144]) by svr1.postgresql.org (Postfix) with ESMTP id 502DD529C0 for ; Mon, 18 Jul 2005 16:32:49 -0300 (ADT) Received: from svr1.postgresql.org ([200.46.204.71]) by localhost (av.hub.org [200.46.204.144]) (amavisd-new, port 10024) with ESMTP id 36311-06 for ; Mon, 18 Jul 2005 19:32:39 +0000 (GMT) Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by svr1.postgresql.org (Postfix) with ESMTP id 4636452AC0 for ; Mon, 18 Jul 2005 16:32:38 -0300 (ADT) 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 j6IJWaw2016395; Mon, 18 Jul 2005 15:32:36 -0400 (EDT) To: Christopher Petrilli Cc: Vivek Khera , pgsql-performance@postgresql.org Subject: Re: Impact of checkpoint_segments under continual load conditions In-reply-to: <59d991c405071811457ccdd3f1@mail.gmail.com> References: <59d991c4050717100874c08a86@mail.gmail.com> <59d991c405071811457ccdd3f1@mail.gmail.com> Comments: In-reply-to Christopher Petrilli message dated "Mon, 18 Jul 2005 14:45:35 -0400" Date: Mon, 18 Jul 2005 15:32:36 -0400 Message-ID: <16394.1121715156@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: by amavisd-new at hub.org X-Spam-Status: No, hits=0.006 tagged_above=0 required=5 tests=AWL X-Spam-Level: X-Archive-Number: 200507/270 X-Sequence-Number: 13511 Christopher Petrilli writes: > http://blog.amber.org/diagrams/comparison_mysql_pgsql.png > Notice the VERY steep drop off. Hmm. Whatever that is, it's not checkpoint's fault. I would interpret the regular upticks in the Postgres times (every several hundred iterations) as being the effects of checkpoints. You could probably smooth out those peaks some with appropriate hacking on bgwriter parameters, but that's not the issue at hand (is it?). I have no idea at all what's causing the sudden falloff in performance after about 10000 iterations. COPY per se ought to be about a constant-time operation, since APPEND is (or should be) constant-time. What indexes, foreign keys, etc do you have on this table? What else was going on at the time? regards, tom lane