Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cCUew-0000JB-9O for pgsql-docs@arkaria.postgresql.org; Thu, 01 Dec 2016 16:56:34 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.84_2) (envelope-from ) id 1cCUev-0007WH-Qe for pgsql-docs@arkaria.postgresql.org; Thu, 01 Dec 2016 16:56:33 +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 1cCUeu-0007Vv-Vt for pgsql-docs@postgresql.org; Thu, 01 Dec 2016 16:56:33 +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 4.84_2) (envelope-from ) id 1cCUer-00078Q-F2 for pgsql-docs@postgresql.org; Thu, 01 Dec 2016 16:56:31 +0000 Received: from [192.168.1.60] (spinlock.commandprompt.com [69.168.55.30]) by lists.commandprompt.com (Postfix) with ESMTPA id F24295CA; Thu, 1 Dec 2016 08:56:21 -0800 (PST) Received: from c-73-225-27-179.hsd1.wa.comcast.net ([73.225.27.179] helo=[192.168.1.60]) by assp.commandprompt.com with SMTPSA(TLSv1_2 ECDHE-RSA-AES128-GCM-SHA256) (2.5.1); 1 Dec 2016 08:56:21 -0800 Subject: Re: Needs discussion of pg_xlog To: robert@interactive.co.uk, pgsql-docs@postgresql.org References: <20161201150006.4377.8523@wrigleys.postgresql.org> From: "Joshua D. Drake" Organization: Command Prompt, Inc. Message-ID: <5414c450-db82-8169-d5cf-f33339d0944c@commandprompt.com> Date: Thu, 1 Dec 2016 08:56:20 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20161201150006.4377.8523@wrigleys.postgresql.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Assp-Version: 2.5.1(16177) on assp.commandprompt.com X-Assp-ID: assp.commandprompt.com m1-11381-02075 X-Assp-Session: 7FC97558CF38 (mail 1) X-Assp-Original-Subject: Re: [DOCS] Needs discussion of pg_xlog X-Assp-Client-SSL: yes X-Pg-Spam-Score: -4.8 (----) List-Archive: List-Help: List-ID: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: X-Mailing-List: pgsql-docs Precedence: bulk Sender: pgsql-docs-owner@postgresql.org On 12/01/2016 07:00 AM, robert@interactive.co.uk wrote: > The following documentation comment has been logged on the website: > > Page: https://www.postgresql.org/docs/9.4/static/runtime-config-file-locations.html > Description: > > In various places (e.g. stackoverflow), I've seen people suggest having > pg_xlog ion a different disk (i.e. not in /var/lib/pgsql/9.X/data). > > The only mention of this that I've seen is in Section 29.5 (WAL Internals), > and that just says "it is advantageous...", with no explanation. > > If this IS a good idea, then "Server Configuration / File Locations" is > where it should be discussed: in particular, why is it a good idea, and how > does it affect backups (and in particular base backups to a standby server). The reason it can be advantageous is that pg_xlog has a different write profile that $PGDATA. The WAL is written sequentially versus randomly. JD > -- Command Prompt, Inc. http://the.postgres.company/ +1-503-667-4564 PostgreSQL Centered full stack support, consulting and development. Everyone appreciates your honesty, until you are honest with them. Unless otherwise stated, opinions are my own. -- Sent via pgsql-docs mailing list (pgsql-docs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-docs