docs: Clarify that NULL arg to set_config() means reset to default

Author: David G. Johnston <[email protected]>
Reviewed-by: Zhang Mingli <[email protected]>
Discussion: https://www.postgresql.org/message-id/CAKFQuwY0SK6JdCci1VJX6xsztRXgGeVEY-grkENZx%[email protected]

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 9f531e23283e82acf46de5a2d72887dfb7f9bbbd..0224f93733dc60ebc91ad27499bb98c4f472af88 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -28576,6 +28576,11 @@ acl      | {postgres=arwdDxtm/postgres,foo=r/postgres}
         use <literal>false</literal> instead. This function corresponds to
         the SQL command <xref linkend="sql-set"/>.
        </para>
+       <para>
+        <function>set_config</function> accepts the NULL value for
+        <parameter>new_value</parameter>, but as settings cannot be null, it
+        is interpreted as a request to reset the setting to its default value.
+       </para>
        <para>
         <literal>set_config('log_statement_stats', 'off', false)</literal>
         <returnvalue>off</returnvalue>