Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.84_2) (envelope-from ) id 1d0CPA-0000iR-Gl for pgsql-hackers@arkaria.postgresql.org; Mon, 17 Apr 2017 19:33:44 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.84_2) (envelope-from ) id 1d0CP9-000582-Nz for pgsql-hackers@arkaria.postgresql.org; Mon, 17 Apr 2017 19:33:43 +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 1d0CP8-00056Y-3J for pgsql-hackers@postgresql.org; Mon, 17 Apr 2017 19:33:42 +0000 Received: from sss.pgh.pa.us ([66.207.139.130]) by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1d0CP5-0005Tu-7Q for pgsql-hackers@postgresql.org; Mon, 17 Apr 2017 19:33:40 +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 v3HJXZGt029430; Mon, 17 Apr 2017 15:33:35 -0400 From: Tom Lane To: Dmitry Ivanov cc: pgsql-hackers Subject: Re: Possible problem in Custom Scan API In-reply-to: References: <20021.1491933424@sss.pgh.pa.us> <1ef85b46-1385-4810-bb80-97cd977da1d5@postgrespro.ru> <367.1491940070@sss.pgh.pa.us> <4509.1491944329@sss.pgh.pa.us> <0e0388a6-aa53-42a6-8be9-0d46ccbc788e@postgrespro.ru> <8130.1492013026@sss.pgh.pa.us> Comments: In-reply-to Dmitry Ivanov message dated "Wed, 12 Apr 2017 19:37:57 +0300" MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <29428.1492457615.1@sss.pgh.pa.us> Date: Mon, 17 Apr 2017 15:33:35 -0400 Message-ID: <29429.1492457615@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-hackers Precedence: bulk Sender: pgsql-hackers-owner@postgresql.org Dmitry Ivanov writes: > Tom Lane wrote: >> I'm coming around to the idea that it'd be better to disable physical >> tlists for custom scans. >> However, I'm hesitant to make such a change in the back branches; if >> there's anyone using custom scans who's negatively affected, they'd be >> rightfully unhappy. Are you satisfied if we change this in HEAD? After thinking about this over the weekend, I've come to the conclusion that back-patching is probably the right thing anyway. The upside of the use_physical_tlist optimization is pretty marginal even when it applies, while the downsides of applying it inappropriately can be very large, as we've discussed. > I've been thinking about this all along, and it seems that this is a decent > decision. However, I've made a tiny bugfix patch which allows CustomScans > to notify the core code that they can handle physical targetlists. I'm unimpressed by this part --- we couldn't back-patch such a change, and I think it's unnecessary anyway in 9.6+ because the scan provider could generate a nondefault pathtarget if it wants this to happen. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers