pg_wal_lsn_diff

According to the pg_wal_lsn_diff manual:

pg_wal_lsn_diff ( lsn pg_lsn, lsn pg_lsn ) → numeric

    Calculates the difference in bytes between two write-ahead log
    locations. This can be used with pg_stat_replication or some of
    the functions shown in Table 9.87 to get the replication lag.

It's not clear whether its return value is (first arg - second arg) or
(second arg - first arg). The order matters because the return value
could have a sign (it actually does first arg - second arg). Attached
is a patch to fix the description.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index b7150510ab..2870692164 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -25102,11 +25102,11 @@ SELECT collation for ('foo' COLLATE "de_DE");
         <indexterm>
          <primary>pg_wal_lsn_diff</primary>
         </indexterm>
-        <function>pg_wal_lsn_diff</function> ( <parameter>lsn</parameter> <type>pg_lsn</type>,
<parameter>lsn</parameter><type>pg_lsn</type> )
 
+        <function>pg_wal_lsn_diff</function> ( <parameter>lsn1</parameter> <type>pg_lsn</type>,
<parameter>lsn2</parameter><type>pg_lsn</type> )
 
         <returnvalue>numeric</returnvalue>
        </para>
        <para>
-        Calculates the difference in bytes between two write-ahead log
+        Calculates the difference (ls1 - ls2) in bytes between two write-ahead log
         locations.  This can be used
         with <structname>pg_stat_replication</structname> or some of the
         functions shown in <xref linkend="functions-admin-backup-table"/> to