Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.80) (envelope-from ) id 1VoFOg-0002nW-Ah for pgsql-performance@arkaria.postgresql.org; Wed, 04 Dec 2013 16:33:58 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.80) (envelope-from ) id 1VoFOf-0002IG-HA for pgsql-performance@arkaria.postgresql.org; Wed, 04 Dec 2013 16:33:57 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtp (Exim 4.80) (envelope-from ) id 1VoFOe-0002I6-Lu; Wed, 04 Dec 2013 16:33:56 +0000 Received: from moutng.kundenserver.de ([212.227.126.187]) by magus.postgresql.org with esmtp (Exim 4.80) (envelope-from ) id 1VoFOb-0001dZ-JP; Wed, 04 Dec 2013 16:33:56 +0000 Received: from anarazel.de (p5DDC5FC6.dip0.t-ipconnect.de [93.220.95.198]) by mrelayeu.kundenserver.de (node=mreu4) with ESMTP (Nemesis) id 0LywdQ-1Vb8O71vTE-015521; Wed, 04 Dec 2013 17:33:51 +0100 Received: by anarazel.de (Postfix, from userid 1000) id B08D01019EF; Wed, 4 Dec 2013 17:33:50 +0100 (CET) Date: Wed, 4 Dec 2013 17:33:50 +0100 From: Andres Freund To: Claudio Freire Cc: Metin Doslu , Amit Kapila , pgsql-hackers , postgres performance list Subject: Re: [HACKERS] Parallel Select query performance and shared buffers Message-ID: <20131204163350.GA5756@awork2.anarazel.de> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Provags-ID: V02:K0:5FKXe7hRBvpUof4D1AIw2LTWTjtm5klFEseVGGyO23S p6NkrNo9MvryuSebVFTeCUKfLXO1lICd26nPBeIiaCOvQGNfgw aXnybahj/2aqaeyfPocGD5Xl4GmeLwpvtKHJWURyLp2JAZobJP AvTFzHb1VIighbns+r0+h2mPusLNSzssgPLK2HgWN798c2HUv4 d4Ppt7/GWJ/2PVwZmffbpcgfx4PK1SSSK75KCQFNRwZo636BiP 6cnT8/Uq0n6EuVGse1iZHp8cjjbQhCpncb8CWSsfInFVqZ4X/S KMmx97/rCQoorh/34Ojc0UWj0gm8eLyseq7JhWzXC1r8wkdb+r vml2o8XkgqdV3IJPj3SLgtXly4IkEkMCJtXeASgms X-Pg-Spam-Score: -1.9 (-) List-Archive: List-Help: List-ID: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: X-Mailing-List: pgsql-performance Precedence: bulk Sender: pgsql-performance-owner@postgresql.org On 2013-12-04 14:27:10 -0200, Claudio Freire wrote: > On Wed, Dec 4, 2013 at 9:19 AM, Metin Doslu wrote: > > > > Here are the results of "vmstat 1" while running 8 parallel TPC-H Simple > > (#6) queries: Although there is no need for I/O, "wa" fluctuates between 0 > > and 1. > > > > procs -----------memory---------- ---swap-- -----io---- --system-- > > -----cpu----- > > r b swpd free buff cache si so bi bo in cs us sy id wa st > > 0 0 0 30093568 84892 38723896 0 0 0 0 22 14 0 0 100 0 0 > > 8 1 0 30043056 84892 38723896 0 0 0 0 27080 52708 16 14 70 0 0 > > 8 1 0 30006600 84892 38723896 0 0 0 0 44952 118286 43 44 12 1 0 > > 8 0 0 29986264 84900 38723896 0 0 0 20 28043 95934 49 42 8 1 0 > > 7 0 0 29991976 84900 38723896 0 0 0 0 8308 73641 52 42 6 0 0 > > 0 0 0 30091828 84900 38723896 0 0 0 0 3996 30978 23 24 53 0 0 > > 0 0 0 30091968 84900 38723896 0 0 0 0 17 23 0 0 100 0 0 > > > Notice the huge %sy My bet is on transparent hugepage defragmentation. Alternatively it's scheduler overhead, due to superflous context switches around the buffer mapping locks. I'd strongly suggest doing a "perf record -g -a ; perf report" run to check what's eating up the time. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance