X-Original-To: pgsql-performance-postgresql.org@localhost.postgresql.org Received: from localhost (mx1.hub.org [200.46.208.251]) by postgresql.org (Postfix) with ESMTP id 81AA211F6478 for ; Fri, 28 Apr 2006 02:06:08 -0300 (ADT) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.208.251]) (amavisd-new, port 10024) with ESMTP id 32849-09 for ; Fri, 28 Apr 2006 02:05:57 -0300 (ADT) 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 410B211F6251 for ; Fri, 28 Apr 2006 02:05:56 -0300 (ADT) Received: from sss2.sss.pgh.pa.us (tgl@localhost [127.0.0.1]) by sss.pgh.pa.us (8.13.6/8.13.6) with ESMTP id k3S55mgi025361; Fri, 28 Apr 2006 01:05:48 -0400 (EDT) To: guoping.zhang@nec.com.au cc: "'Simon Riggs'" , pgsql-performance@postgresql.org, "'Guoping Zhang (E-mail)'" Subject: Re: how unsafe (or worst scenarios) when setting fsync In-reply-to: <004201c66a80$c8f86d00$74304c93@eddy> References: <004201c66a80$c8f86d00$74304c93@eddy> Comments: In-reply-to "Guoping Zhang" message dated "Fri, 28 Apr 2006 15:01:17 +1000" Date: Fri, 28 Apr 2006 01:05:48 -0400 Message-ID: <25360.1146200748@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200604/661 X-Sequence-Number: 18745 "Guoping Zhang" writes: > But altering the commit_delay from 1 to 100000, I observed that there is no > time difference for the operation. Why is that? As our tests consists of > 10000 small transactions which completed in 66 seconds, that is, about 160 > transactions per second. When commit_delay set to 100000 (i.e., 0.1 second), > that in theory, shall group around 16 transactions into one commit, but > result is same from the repeated test. Am I mistaken something here? commit_delay can only help if there are multiple clients issuing transactions concurrently, so that there are multiple commits pending at the same instant. If you are issuing one serial stream of transactions, it's useless. If you do have multiple active clients, then we need to look more closely; but your statement does not indicate that. regards, tom lane