Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eZ0eP-000641-Oa for pgsql-general@arkaria.postgresql.org; Tue, 09 Jan 2018 20:37:37 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.84_2) (envelope-from ) id 1eZ0eP-0003Cj-9Y for pgsql-general@arkaria.postgresql.org; Tue, 09 Jan 2018 20:37:37 +0000 Received: from makus.postgresql.org ([2001:4800:1501:1::229]) by malur.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1eZ0eO-0003CY-V9 for pgsql-general@lists.postgresql.org; Tue, 09 Jan 2018 20:37:37 +0000 Received: from lists.commandprompt.com ([2604:da00:2:2:5054:ff:fe07:7618]) by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1eZ0eL-0006UU-BO for pgsql-general@lists.postgresql.org; Tue, 09 Jan 2018 20:37:35 +0000 Received: from [192.168.1.8] (spinlock.commandprompt.com [69.168.55.30]) by lists.commandprompt.com (Postfix) with ESMTPA id 503AE7E4; Tue, 9 Jan 2018 12:37:30 -0800 (PST) Received: from c-67-170-3-120.hsd1.wa.comcast.net ([67.170.3.120] helo=[192.168.1.8]) by assp.commandprompt.com with SMTPSA(TLSv1_2 ECDHE-RSA-AES128-GCM-SHA256) (2.5.1); 9 Jan 2018 12:37:29 -0800 Subject: Re: data-checksums To: Andres Freund , Rakesh Kumar Cc: Alvaro Herrera , Stephen Frost , "pgsql-general@lists.postgresql.org" References: <20180109184149.ih4ore4c4axwizor@alvherre.pgsql> <20180109202259.cpszfiavep42pp6v@alap3.anarazel.de> From: "Joshua D. Drake" Organization: Command Prompt, Inc. Message-ID: <163ee8df-cae2-484e-5791-c74994d33403@commandprompt.com> Date: Tue, 9 Jan 2018 12:37:16 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: <20180109202259.cpszfiavep42pp6v@alap3.anarazel.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Assp-Version: 2.5.1(16177) on assp.commandprompt.com X-Assp-ID: assp.commandprompt.com m1-30250-00951 X-Assp-Session: 7FF97C413A80 (mail 1) X-Assp-Original-Subject: Re: data-checksums X-Assp-Client-SSL: yes List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk On 01/09/2018 12:22 PM, Andres Freund wrote: > On 2018-01-09 20:04:04 +0100, Rakesh Kumar wrote: >>>> I also would like to believe that the hit is small, but when PG >>>> official document writes "noticeable performance penalty", it becomes >>>> difficult to convince management that the hit is small :-) >>> Why believe, when you can measure? >> yup doing that. But I still feel that PG documentation should stay >> away from such scare mongering. Or did the lawyers write that :) > So we should rather lie about it having a potential for performance > impact? Who'd be helped by that? It isn't a lie, it depends on the workload and hardware. Adjusting the documentation to say something like the following probably isn't a bad idea: The use of the data checksum feature may incur a performance penalty. However, this does depend on your particular workload and provisioned hardware. It is wise to test the feature based on your specific requirements. JD -- Command Prompt, Inc. || http://the.postgres.company/ || @cmdpromptinc PostgreSQL centered full stack support, consulting and development. Advocate: @amplifypostgres || Learn: https://postgresconf.org ***** Unless otherwise stated, opinions are my own. *****