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 1ernna-0006Tq-A1 for pgsql-performance@arkaria.postgresql.org; Fri, 02 Mar 2018 16:44:46 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.89) (envelope-from ) id 1ernnY-0004pC-OY for pgsql-performance@arkaria.postgresql.org; Fri, 02 Mar 2018 16:44:44 +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 4.89) (envelope-from ) id 1ernnY-0004p1-Dr for pgsql-performance@lists.postgresql.org; Fri, 02 Mar 2018 16:44:44 +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 4.89) (envelope-from ) id 1ernnW-0005vI-4h for pgsql-performance@postgresql.org; Fri, 02 Mar 2018 16:44:43 +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 w22Gieq9030034; Fri, 2 Mar 2018 11:44:40 -0500 From: Tom Lane To: Dave Cramer cc: pgsql-performance Subject: Re: why does this query not use a parallel query In-reply-to: References: Comments: In-reply-to Dave Cramer message dated "Fri, 02 Mar 2018 11:29:29 -0500" MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <30032.1520009080.1@sss.pgh.pa.us> Date: Fri, 02 Mar 2018 11:44:40 -0500 Message-ID: <30033.1520009080@sss.pgh.pa.us> List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk Dave Cramer writes: > Have a query: > explain analyze SELECT minion_id FROM mob_player_mob_118 WHERE player_id = > 55351078; > Index Only Scan using mob_player_mob_118_pkey on mob_player_mob_118 > (cost=0.44..117887.06 rows=4623076 width=4) (actual time=0.062..3716.105 > rows=4625123 loops=1) I don't think we have parallel IOS yet (I might be wrong). If so, it probably thinks this is cheaper than the best available parallel plan. > If I just get the count it will use a parallel query Likely a parallelized aggregation. regards, tom lane