Received: from maia.hub.org (maia-5.hub.org [200.46.204.29]) by mail.postgresql.org (Postfix) with ESMTP id BAF32133655C for ; Wed, 26 Jan 2011 09:25:40 -0400 (AST) 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 40742-10 for ; Wed, 26 Jan 2011 13:25:35 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from lo.gmane.org (lo.gmane.org [80.91.229.12]) by mail.postgresql.org (Postfix) with ESMTP id 5E7D8133616B for ; Wed, 26 Jan 2011 09:25:33 -0400 (AST) Received: from list by lo.gmane.org with local (Exim 4.69) (envelope-from ) id 1Pi5NK-00013M-IP for pgsql-performance@postgresql.org; Wed, 26 Jan 2011 14:25:30 +0100 Received: from lara.cc.fer.hr ([161.53.72.113]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 26 Jan 2011 14:25:30 +0100 Received: from ivoras by lara.cc.fer.hr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 26 Jan 2011 14:25:30 +0100 X-Injected-Via-Gmane: http://gmane.org/ To: pgsql-performance@postgresql.org From: Ivan Voras Subject: Re: Queries becoming slow under heavy load Date: Wed, 26 Jan 2011 14:25:17 +0100 Lines: 13 Message-ID: References: <945629628BB0174D86709AFE6D1CDEF5016342E3@SP-EXCHMBC.sp.corp.collab.net> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@dough.gmane.org X-Gmane-NNTP-Posting-Host: lara.cc.fer.hr User-Agent: Mozilla/5.0 (X11; U; FreeBSD amd64; en-US; rv:1.9.2.12) Gecko/20101102 Thunderbird/3.1.6 In-Reply-To: <945629628BB0174D86709AFE6D1CDEF5016342E3@SP-EXCHMBC.sp.corp.collab.net> X-Enigmail-Version: 1.1.2 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: 201101/240 X-Sequence-Number: 42027 On 25/01/2011 22:37, Anne Rosset wrote: > Hi, > > We are running some performances tests. With a lot of concurrent > access, queries get very slow. When there is no load, those queries run > fast. As others said, you need to stat how many concurrent clients are working on the database and also the number of logical CPUs (CPU cores, hyperthreading) are present in the machine. So far, as a rule of thumb, if you have more concurrent active connections (i.e. doing queries, not idling), you will experience a sharp decline in performance if this number exceeds the number of logical CPUs in the machine.