Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.80) (envelope-from ) id 1Ysvx3-0005qL-7K for pgsql-admin@arkaria.postgresql.org; Thu, 14 May 2015 16:25:37 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.80) (envelope-from ) id 1Ysvx2-0001F5-O8 for pgsql-admin@arkaria.postgresql.org; Thu, 14 May 2015 16:25:36 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtps (TLS1.2:RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1Ysvx2-0001Ey-0j for pgsql-admin@postgresql.org; Thu, 14 May 2015 16:25:36 +0000 Received: from sss.pgh.pa.us ([66.207.139.130]) by magus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.84) (envelope-from ) id 1Ysvwz-00029W-BZ for pgsql-admin@postgresql.org; Thu, 14 May 2015 16:25:35 +0000 Received: from sss1.sss.pgh.pa.us (localhost [127.0.0.1]) by sss.pgh.pa.us (8.14.4/8.14.4) with ESMTP id t4EGPSX3004615; Thu, 14 May 2015 12:25:28 -0400 From: Tom Lane To: Ravi Krishna cc: pgsql-admin@postgresql.org Subject: Re: WAL and O_DIRECT In-reply-to: <14d532dde85-2108-310a1@webstg-m03.mail.aol.com> References: <21483.1431618933@sss.pgh.pa.us> <14d532dde85-2108-310a1@webstg-m03.mail.aol.com> Comments: In-reply-to Ravi Krishna message dated "Thu, 14 May 2015 12:07:04 -0400" Date: Thu, 14 May 2015 12:25:28 -0400 Message-ID: <4614.1431620728@sss.pgh.pa.us> X-Pg-Spam-Score: -1.9 (-) List-Archive: List-Help: List-ID: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: X-Mailing-List: pgsql-admin Precedence: bulk Sender: pgsql-admin-owner@postgresql.org Ravi Krishna writes: > Am I right in concluding that PG WAL writes without underlying h/w caching is not crash proof. We expect that the hardware+OS honors fsync() correctly, ie puts the data on durable storage before fsync returns. That does not mean anything one way or the other about caching, it just means that the filesystem stack has to be correctly implemented. regards, tom lane -- Sent via pgsql-admin mailing list (pgsql-admin@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin