From 4e0c743c18bf5435a4850510c5c74b3521c3e1e5 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 8 Mar 2018 11:25:26 -0500
Subject: Fix cross-checking of
 ReservedBackends/max_wal_senders/MaxConnections.

We were independently checking ReservedBackends < MaxConnections and
max_wal_senders < MaxConnections, but because walsenders aren't allowed
to use superuser-reserved connections, that's really the wrong thing.
Correct behavior is to insist on ReservedBackends + max_wal_senders being
less than MaxConnections.  Fix the code and associated documentation.

This has been wrong for a long time, but since the situation probably
hardly ever arises in the field (especially pre-v10, when the default
for max_wal_senders was zero), no back-patch.

Discussion: https://postgr.es/m/28271.1520195491@sss.pgh.pa.us
---
 doc/src/sgml/config.sgml | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

(limited to 'doc/src')

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 259a2d83b4a..3a8fc7d803c 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -696,8 +696,9 @@ include_dir 'conf.d'
 
        <para>
         The default value is three connections. The value must be less
-        than the value of <varname>max_connections</varname>. This
-        parameter can only be set at server start.
+        than <varname>max_connections</varname> minus
+        <xref linkend="guc-max-wal-senders"/>.
+        This parameter can only be set at server start.
        </para>
       </listitem>
      </varlistentry>
@@ -2982,13 +2983,16 @@ include_dir 'conf.d'
         maximum number of simultaneously running WAL sender
         processes). The default is 10. The value 0 means replication is
         disabled. WAL sender processes count towards the total number
-        of connections, so the parameter cannot be set higher than
-        <xref linkend="guc-max-connections"/>.  Abrupt streaming client
-        disconnection might cause an orphaned connection slot until
+        of connections, so this parameter's value must be less than
+        <xref linkend="guc-max-connections"/> minus
+        <xref linkend="guc-superuser-reserved-connections"/>.
+        Abrupt streaming client disconnection might leave an orphaned
+        connection slot behind until
         a timeout is reached, so this parameter should be set slightly
         higher than the maximum number of expected clients so disconnected
         clients can immediately reconnect.  This parameter can only
-        be set at server start. <varname>wal_level</varname> must be set to
+        be set at server start.
+        Also, <varname>wal_level</varname> must be set to
         <literal>replica</literal> or higher to allow connections from standby
         servers.
        </para>
@@ -3007,10 +3011,11 @@ include_dir 'conf.d'
          (see <xref linkend="streaming-replication-slots"/>) that the server
          can support. The default is 10.  This parameter can only be set at
          server start.
-         <varname>wal_level</varname> must be set
-         to <literal>replica</literal> or higher to allow replication slots to
-         be used. Setting it to a lower value than the number of currently
+         Setting it to a lower value than the number of currently
          existing replication slots will prevent the server from starting.
+         Also, <varname>wal_level</varname> must be set
+         to <literal>replica</literal> or higher to allow replication slots to
+         be used.
         </para>
        </listitem>
       </varlistentry>
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