Received: from maia.hub.org (maia-5.hub.org [200.46.204.29]) by mail.postgresql.org (Postfix) with ESMTP id 648A41337BEB for ; Sun, 1 May 2011 13:17:21 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.29]) (amavisd-maia, port 10024) with ESMTP id 67499-06 for ; Sun, 1 May 2011 16:17:13 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from sss.pgh.pa.us (sss.pgh.pa.us [66.207.139.130]) by mail.postgresql.org (Postfix) with ESMTP id 9E6A11337BD2 for ; Sun, 1 May 2011 13:17:12 -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 p41GHAsL018736; Sun, 1 May 2011 12:17:11 -0400 (EDT) To: Javier Reyes cc: pgsql-admin@postgresql.org Subject: Re: Option shared_buffers in PostgreSQL In-reply-to: References: Comments: In-reply-to Javier Reyes message dated "Sun, 01 May 2011 12:20:15 +0100" Date: Sun, 01 May 2011 12:17:10 -0400 Message-ID: <18735.1304266630@sss.pgh.pa.us> From: Tom Lane X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-1.91 tagged_above=-10 required=5 tests=BAYES_00=-1.9, T_RP_MATCHES_RCVD=-0.01 X-Spam-Level: X-Archive-Number: 201105/3 X-Sequence-Number: 37440 Javier Reyes writes: > I have a server with 4GB of RAM and PostgreSQL 9.0.3 on Centos 5. I'm using > pgbench and pgbench-tools to measure performance, using two pgbench-tools > queries: select and tpc-b. > With default settings of postgresql.conf and select query, I get the > following results: > Scale: 1, 10, 100, 1000. > Transactions per second: 10000, 8800, 7500, 100. These numbers look like complete junk from here. I suspect you were using a number-of-transactions parameter that's too small to give stable answers. If you don't have the value set high enough so that each pgbench run lasts at least a couple of minutes, I wouldn't put any credence in the results. See also the other "good practices" mentioned at the bottom of the pgbench documentation page. regards, tom lane