From b460f5d6693103076dc554aa7cbb96e1e53074f9 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Fri, 2 Dec 2016 07:42:58 -0500
Subject: Add max_parallel_workers GUC.

Increase the default value of the existing max_worker_processes GUC
from 8 to 16, and add a new max_parallel_workers GUC with a maximum
of 8.  This way, even if the maximum amount of parallel query is
happening, there is still room for background workers that do other
things, as originally envisioned when max_worker_processes was added.

Julien Rouhaud, reviewed by Amit Kapila and by revised by me.
---
 doc/src/sgml/config.sgml | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index b1c5289fccc..fdf8b3e9c77 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1982,7 +1982,7 @@ include_dir 'conf.d'
         <para>
          Sets the maximum number of background processes that the system
          can support.  This parameter can only be set at server start.  The
-         default is 8.
+         default is 16.
         </para>
 
         <para>
@@ -2004,8 +2004,9 @@ include_dir 'conf.d'
          Sets the maximum number of workers that can be started by a single
          <literal>Gather</literal> node.  Parallel workers are taken from the
          pool of processes established by
-         <xref linkend="guc-max-worker-processes">.  Note that the requested
-         number of workers may not actually be available at run time.  If this
+         <xref linkend="guc-max-worker-processes">, limited by
+         <xref linkend="guc-max-parallel-workers">.  Note that the requested
+         number of workers may not actually be available at runtime.  If this
          occurs, the plan will run with fewer workers than expected, which may
          be inefficient.  The default value is 2.  Setting this value to 0
          disables parallel query execution.
@@ -2034,6 +2035,22 @@ include_dir 'conf.d'
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-parallel-workers" xreflabel="max_parallel_workers">
+       <term><varname>max_parallel_workers</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_parallel_workers</> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Sets the maximum number of workers that the system can support for
+         parallel queries.  The default value is 8.  When increasing or
+         decreasing this value, consider also adjusting
+         <xref linkend="guc-max-parallel-workers-per-gather">.
+        </para>
+       </listitem>
+      </varlistentry>
+
       <varlistentry id="guc-backend-flush-after" xreflabel="backend_flush_after">
        <term><varname>backend_flush_after</varname> (<type>integer</type>)
        <indexterm>
-- 
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