Received: from localhost (unknown [200.46.204.184]) by postgresql.org (Postfix) with ESMTP id 63B7B2E00A4 for ; Tue, 4 Mar 2008 10:04:37 -0400 (AST) Received: from postgresql.org ([200.46.204.71]) by localhost (mx1.hub.org [200.46.204.184]) (amavisd-maia, port 10024) with ESMTP id 63880-07 for ; Tue, 4 Mar 2008 10:04:23 -0400 (AST) X-Greylist: from auto-whitelisted by SQLgrey-1.7.5 Received: from ciao.gmane.org (main.gmane.org [80.91.229.2]) by postgresql.org (Postfix) with ESMTP id 4DD912E008A for ; Tue, 4 Mar 2008 10:04:31 -0400 (AST) Received: from list by ciao.gmane.org with local (Exim 4.43) id 1JWXkl-0007zV-CZ for pgsql-performance@postgresql.org; Tue, 04 Mar 2008 14:04:23 +0000 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 ; Tue, 04 Mar 2008 14:04:23 +0000 Received: from ivoras by lara.cc.fer.hr with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 04 Mar 2008 14:04:23 +0000 X-Injected-Via-Gmane: http://gmane.org/ To: pgsql-performance@postgresql.org From: Ivan Voras Subject: Re: Performance tuning on FreeBSD Date: Tue, 04 Mar 2008 15:07:57 +0100 Lines: 18 Message-ID: References: <892916310803031539scffd5bchcce5a848b3a57a32@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: lara.cc.fer.hr User-Agent: Thunderbird 2.0.0.6 (X11/20071022) In-Reply-To: X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=0 tagged_above=0 required=5 tests=AWL=0.000 X-Spam-Level: X-Archive-Number: 200803/48 X-Sequence-Number: 29002 Greg Smith wrote: > On Mon, 3 Mar 2008, alan bryan wrote: > >>> pgbench -c 100 -t 1000 testdb >> tps = 558.013714 (excluding connections establishing) >> >> Just for testing, I tried turning off fsync and got: >> tps = 4061.662041 (excluding connections establishing) > > This is odd. ~500 is what I expect from this test when there is no > write cache to accelerate fsync, while ~4000 is normal for your class of > hardware when you have such a cache. I'm curious about the math behind this - is ~4000 burst or sustained rate? For common BBU cache sizes (256M, 512M), filling that amount with data is pretty trivial. When the cache is full, new data can enter the cache only at a rate at which old data is evacuated from the cache (to the drive), which is at "normal", uncached disk drive speeds.