Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jgajY-0001Sg-8N for pgsql-performance@arkaria.postgresql.org; Wed, 03 Jun 2020 21:15:36 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.92) (envelope-from ) id 1jgajW-0006Ra-9s for pgsql-performance@arkaria.postgresql.org; Wed, 03 Jun 2020 21:15:34 +0000 Received: from makus.postgresql.org ([2001:4800:3e1:1::229]) by malur.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jgajV-0006RT-Ta for pgsql-performance@lists.postgresql.org; Wed, 03 Jun 2020 21:15:34 +0000 Received: from mail-io1-xd33.google.com ([2607:f8b0:4864:20::d33]) by makus.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jgajS-000832-UQ for pgsql-performance@lists.postgresql.org; Wed, 03 Jun 2020 21:15:32 +0000 Received: by mail-io1-xd33.google.com with SMTP id s18so3993481ioe.2 for ; Wed, 03 Jun 2020 14:15:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=telsasoft-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=RyA2241m/q308HNoAP2hDdwhWDChsHG1/vzuN0MNzdo=; b=DYjBrO41KQ+QpDcqOG8hYVz9YoW7m377R9cHhVt4dTrqxzA9+1ma7zvzUsd+EGZ87V 74CsDsBKvjUM1CZVkhU6MVKehrmmbyuHo62PbfV3RbmS+ex+fNnWn5fkJpi6hsuA3We5 tYYEGBy71RARmHbRu5EiaQ6i+IHXZKZq2zQHu6BagjbiOai3gAsR0v/WOwfWFASGojrx wIMtInMsma+LCLQs51GluOkHAOzPPJ83lgyL6yIBvK8tgQFLOEDI/NmPC+tnx6GQyfcs 2baAIQU7VvZxUgKddD6LoSEkObH1P9NO+VVFZYoo5uPrChMJuDNbtrmfp4D+yoXHye99 5gUA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=RyA2241m/q308HNoAP2hDdwhWDChsHG1/vzuN0MNzdo=; b=sN2WHF8Dt42D/J7Cuw5yCNNa7BrrqxjBcKYL+Ic8tEmWdy24txMqSQB8Il8SvZlcsG YqSam1NScJ1TJQgcbU2lgc6i/Uk85PC9YtdZt1HZzx3GiOmNUDNd4rkg7ek81u48r71k QrC1FT0Vsxf265mhnpiWpAaEXkHeQJIKaJNcmXrOl/u2f5tyvo7Kzce1K+0Gm9S3ivwq RAa3q+MxUGm46NiDTGo86lig3bLJfXiPSzbBXwoWu03XTQW2udsrgW0Y1h+o27rlcbxF Ib8n0AH4E/ZP2tP3jJmW146MiSMavUBB9SEq8xbS3ftKMvsP8jOtpXuGKIDZQn59WCVB WhHw== X-Gm-Message-State: AOAM532Zubq6kCtUZI2jaEkyDn7W2VhVcf7SBMLV+6NkdLWZtxLq7DI3 2w9LrEwJ9M2n4tECQXrZxG68Uw== X-Google-Smtp-Source: ABdhPJwKU8z99AHgmdsunGL9FfVM8TIwdLwpcWDDrQsB9JLDhAakZFL/InYGj3EwpfuBxh2Dk2g7Tw== X-Received: by 2002:a02:5184:: with SMTP id s126mr1656053jaa.30.1591218929435; Wed, 03 Jun 2020 14:15:29 -0700 (PDT) Received: from pryzbyj.telsasoft (charmander.telsasoft.com. [50.244.222.1]) by smtp.gmail.com with ESMTPSA id d11sm1396737iod.11.2020.06.03.14.15.28 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 03 Jun 2020 14:15:28 -0700 (PDT) Received: by pryzbyj.telsasoft (Postfix, from userid 1000) id BAAF680052B; Wed, 3 Jun 2020 16:15:26 -0500 (CDT) Date: Wed, 3 Jun 2020 16:15:26 -0500 From: Justin Pryzby To: Philip Semanchuk Cc: pgsql-performance@lists.postgresql.org Subject: Re: increased max_parallel_workers_per_gather results in fewer workers? Message-ID: <20200603211526.GU30144@telsasoft.com> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk On Wed, Jun 03, 2020 at 04:04:13PM -0400, Philip Semanchuk wrote: > Can anyone help me understand why this happens, or where I might look for clues? What version postgres ? Can you reproduce if you do: ALTER SYSTEM SET max_parallel_workers_per_gather=0; SELECT pg_reload_conf(); .. and then within the session do: SET max_parallel_workers_per_gather=12; I guess you should show an explain analyze, specifically "Workers Planned/Launched", maybe by linking to explain.depesz.com -- Justin