Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1gK8iN-0007Do-Ek for pgsql-hackers@arkaria.postgresql.org; Tue, 06 Nov 2018 21:16:47 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.89) (envelope-from ) id 1gK8iL-0000uM-VC for pgsql-hackers@arkaria.postgresql.org; Tue, 06 Nov 2018 21:16:45 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1gK8iK-0000tA-JC for pgsql-hackers@lists.postgresql.org; Tue, 06 Nov 2018 21:16:45 +0000 Received: from wout2-smtp.messagingengine.com ([64.147.123.25]) by magus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1gK8iG-0001Cm-Fh for pgsql-hackers@postgresql.org; Tue, 06 Nov 2018 21:16:44 +0000 Received: from compute7.internal (compute7.nyi.internal [10.202.2.47]) by mailout.west.internal (Postfix) with ESMTP id 83A1DECE; Tue, 6 Nov 2018 16:16:37 -0500 (EST) Received: from mailfrontend2 ([10.202.2.163]) by compute7.internal (MEProxy); Tue, 06 Nov 2018 16:16:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:content-type :date:from:in-reply-to:message-id:mime-version:references :subject:to:x-me-proxy:x-me-proxy:x-me-sender:x-me-sender :x-sasl-enc; s=fm1; bh=EOTkD+kwv74AQYQh3UNeTgRdt2EPiMxkhsIGdrlam dg=; b=cMF3rE0wa61skNVptEtY1YHnWqr+zGKZO9d+iUvPXhiW9Cl9vuTRePEzF NxeFXfT6CoQDBW8K29VqoYaGY2U0QxgbNFQ3hhOlNExQ+drGzAPl27rLt01pKEU7 102mEZUr92ljJJ41bIUv71kfXw4hFY/gI7H7f25Sct8807WY1LVU3QG1cPY1C19X C9zNyARoneHdvhiYXo5T6sJPrmsstWRN7DmRd05VnUB6V8OUpXSb7Strg2JMvenq WQaE5gZWkIhY6cWqJ7nA9DAy9Tfr8kdxH32yINz33HkXYQTo/3B9xeK9ZTeDhIs5 CWyyBcl/k7cENdFiACTKdIqHGt5Ww== X-ME-Sender: X-ME-Proxy: Received: from april.pezone.net (p5df295f3.dip0.t-ipconnect.de [93.242.149.243]) by mail.messagingengine.com (Postfix) with ESMTPA id AAECA102DD; Tue, 6 Nov 2018 16:16:34 -0500 (EST) Subject: Re: [HACKERS] generated columns To: Simon Riggs References: <1bc948f8-3bab-6c54-50af-c0723a75b85f@2ndquadrant.com> <20180116063546.GA3679@paquier.xyz> <48502d9b-60c4-5b10-40a2-e34f562132b4@2ndquadrant.com> <20180119051804.GC12826@paquier.xyz> <2e3d5147-16f8-af0f-00ab-4c72cafc896f@2ndquadrant.com> <20180131131804.GB1586@paquier.xyz> <20180202022532.GA84623@paquier.xyz> <050e663d-d915-f61b-af96-5a09c10ade02@2ndquadrant.com> <79e4de23-52e3-2c45-9ba0-5f6932f590aa@2ndquadrant.com> <28574501540912440@iva5-750e13568e4d.qloud-c.yandex.net> <728602640f3ad29c5a355b9ff50377b7@xs4all.nl> <6c9cc29a-64eb-d033-0909-b93f3a2b8c63@2ndquadrant.com> Cc: Erik Rijkers , Sergei Kornilov , PostgreSQL-development , Michael Paquier , Jaime Casanova From: Peter Eisentraut Openpgp: preference=signencrypt Autocrypt: addr=peter.eisentraut@2ndquadrant.com; 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Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk On 06/11/2018 14:28, Simon Riggs wrote: > The simplest solution would be to exclude generated columns from the > replication stream altogether. > > > IMHO... > > Virtual generated columns need not be WAL-logged, or sent. right > Stored generated columns should be treated just like we'd treat a column > value added by a trigger. > > e.g. if we had a Timestamp column called LastUpdateTimestamp we would > want to send that value Generated columns cannot have volatile expression results in them, so this case cannot happen. Also, we don't know whether the generation expression on the target is the same (or even if it looks the same, consider locale issues etc.), so we need to recompute the generated columns on the target anyway, so it's pointless to send the already computed stored values. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services