Add SETTINGS option to EXPLAIN, to print modified settings.

Query planning is affected by a number of configuration options, and it
may be crucial to know which of those options were set to non-default
values.  With this patch you can say EXPLAIN (SETTINGS ON) to include
that information in the query plan.  Only options affecting planning,
with values different from the built-in default are printed.

This patch also adds auto_explain.log_settings option, providing the
same capability in auto_explain module.

Author: Tomas Vondra
Reviewed-by: Rafia Sabih, John Naylor
Discussion: https://postgr.es/m/[email protected]

2 files changed, 30 insertions, 0 deletions

diff --git a/doc/src/sgml/auto-explain.sgml b/doc/src/sgml/auto-explain.sgml
index 120b168d455..da16164387a 100644
--- a/doc/src/sgml/auto-explain.sgml
+++ b/doc/src/sgml/auto-explain.sgml
@@ -171,6 +171,24 @@ LOAD 'auto_explain';
 
    <varlistentry>
     <term>
+     <varname>auto_explain.log_settings</varname> (<type>boolean</type>)
+     <indexterm>
+      <primary><varname>auto_explain.log_settings</varname> configuration parameter</primary>
+     </indexterm>
+    </term>
+    <listitem>
+     <para>
+      <varname>auto_explain.log_settings</varname> controls whether information
+      about modified configuration options are printed when execution plan is logged.
+      Only options affecting query planning with value different from the built-in
+      default value are included in the output.  This parameter is off by default.
+      Only superusers can change this setting.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term>
      <varname>auto_explain.log_format</varname> (<type>enum</type>)
      <indexterm>
       <primary><varname>auto_explain.log_format</varname> configuration parameter</primary>
diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml
index 8dc0d7038ac..385d10411fa 100644
--- a/doc/src/sgml/ref/explain.sgml
+++ b/doc/src/sgml/ref/explain.sgml
@@ -39,6 +39,7 @@ EXPLAIN [ ANALYZE ] [ VERBOSE ] <replaceable class="parameter">statement</replac
     ANALYZE [ <replaceable class="parameter">boolean</replaceable> ]
     VERBOSE [ <replaceable class="parameter">boolean</replaceable> ]
     COSTS [ <replaceable class="parameter">boolean</replaceable> ]
+    SETTINGS [ <replaceable class="parameter">boolean</replaceable> ]
     BUFFERS [ <replaceable class="parameter">boolean</replaceable> ]
     TIMING [ <replaceable class="parameter">boolean</replaceable> ]
     SUMMARY [ <replaceable class="parameter">boolean</replaceable> ]
@@ -153,6 +154,17 @@ ROLLBACK;
    </varlistentry>
 
    <varlistentry>
+    <term><literal>SETTINGS</literal></term>
+    <listitem>
+     <para>
+      Include information on configuration parameters.  Specifically, include
+      options affecting query planning with value different from the built-in
+      default value.  This parameter defaults to <literal>FALSE</literal>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
     <term><literal>BUFFERS</literal></term>
     <listitem>
      <para>