Doc: Add relfrozenxid Tip to XID wraparound section.

VACUUM VERBOSE and autovacuum log reports were taught to report the
details of how VACUUM advanced relfrozenxid (and relminmxid) by commit
872770fd.  Highlight this by adding a "Tip" to the documentation, next
to related discussion of age(relfrozenxid) monitoring.

Author: Peter Geoghegan <pg@bowt.ie>
Discussion: https://postgr.es/m/CAH2-Wzk0C1O-MKkOrj4YAfsGRru2=cA2VQpqM-9R1HNuG3nFaQ@mail.gmail.com

diff --git a/doc/src/sgml/maintenance.sgml b/doc/src/sgml/maintenance.sgml
index 5f3b6720e41a616d1906e9efd12821e0e8b21cc1..84fba9dcb10795db446452095632021a57e1436a 100644 (file)
--- a/doc/src/sgml/maintenance.sgml
+++ b/doc/src/sgml/maintenance.sgml
@@ -611,6 +611,19 @@ SELECT datname, age(datfrozenxid) FROM pg_database;
     cutoff XID to the current transaction's XID.
    </para>
 
+   <tip>
+    <para>
+     When the <command>VACUUM</command> command's <literal>VERBOSE</literal>
+     parameter is specified, <command>VACUUM</command> prints various
+     statistics about the table.  This includes information about how
+     <structfield>relfrozenxid</structfield> and
+     <structfield>relminmxid</structfield> advanced.  The same details appear
+     in the server log when autovacuum logging (controlled by <xref
+      linkend="guc-log-autovacuum-min-duration"/>) reports on a
+     <command>VACUUM</command> operation executed by autovacuum.
+    </para>
+   </tip>
+
    <para>
     <command>VACUUM</command> normally only scans pages that have been modified
     since the last vacuum, but <structfield>relfrozenxid</structfield> can only be