Add syslog_sequence_numbers parameter

Reviewed-by: Andreas Karlsson <andreas@proxel.se>

doc/src/sgml/config.sgml

@@ -4305,6 +4305,34 @@ local0.*    /var/log/postgresql
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-syslog-sequence-numbers" xreflabel="syslog_sequence_numbers">
+       <term><varname>syslog_sequence_numbers</varname> (<type>boolean</type>)
+        <indexterm>
+         <primary><varname>syslog_sequence_numbers</> configuration parameter</primary>
+        </indexterm>
+       </term>
+
+       <listitem>
+        <para>
+         When logging to <application>syslog</application> and this is on (the
+         default), then each message will be prefixed by an increasing
+         sequence number (such as <literal>[2]</literal>).  This circumvents
+         the <quote>--- last message repeated N times ---</quote> suppression
+         that many syslog implementations perform by default.  In more modern
+         syslog implementations, repeat message suppression can be configured
+         (for example, <literal>$RepeatedMsgReduction</literal>
+         in <productname>rsyslog</productname>), so this might not be
+         necessary.  Also, you could turn this off if you actually want to
+         suppress repeated messages.
+        </para>
+
+        <para>
+         This parameter can only be set in the <filename>postgresql.conf</>
+         file or on the server command line.
+        </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-event-source" xreflabel="event_source">
       <term><varname>event_source</varname> (<type>string</type>)
       <indexterm>

src/backend/utils/error/elog.c

@@ -106,6 +106,7 @@ int			Log_error_verbosity = PGERROR_VERBOSE;
 char	   *Log_line_prefix = NULL;		/* format for extra log line info */
 int			Log_destination = LOG_DESTINATION_STDERR;
 char	   *Log_destination_string = NULL;
+bool		syslog_sequence_numbers = true;
 
 #ifdef HAVE_SYSLOG
 
@@ -2018,7 +2019,11 @@ write_syslog(int level, const char *line)
 
 			chunk_nr++;
 
-			syslog(level, "[%lu-%d] %s", seq, chunk_nr, buf);
+			if (syslog_sequence_numbers)
+				syslog(level, "[%lu-%d] %s", seq, chunk_nr, buf);
+			else
+				syslog(level, "[%d] %s", chunk_nr, buf);
+
 			line += buflen;
 			len -= buflen;
 		}
@@ -2026,7 +2031,10 @@ write_syslog(int level, const char *line)
 	else
 	{
 		/* message short enough */
-		syslog(level, "[%lu] %s", seq, line);
+		if (syslog_sequence_numbers)
+			syslog(level, "[%lu] %s", seq, line);
+		else
+			syslog(level, "%s", line);
 	}
 }
 #endif   /* HAVE_SYSLOG */

src/backend/utils/misc/guc.c

@@ -1632,6 +1632,16 @@ static struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"syslog_sequence_numbers", PGC_SIGHUP, LOGGING_WHERE,
+			gettext_noop("Add sequence number to syslog messags to avoid duplicate suppression."),
+			NULL
+		},
+		&syslog_sequence_numbers,
+		true,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL

src/backend/utils/misc/postgresql.conf.sample

@@ -358,6 +358,7 @@
 # These are relevant when logging to syslog:
 #syslog_facility = 'LOCAL0'
 #syslog_ident = 'postgres'
+#syslog_sequence_numbers = on
 
 # This is only relevant when logging to eventlog (win32):
 #event_source = 'PostgreSQL'

src/include/utils/elog.h

@@ -397,6 +397,7 @@ extern int	Log_error_verbosity;
 extern char *Log_line_prefix;
 extern int	Log_destination;
 extern char *Log_destination_string;
+extern bool syslog_sequence_numbers;
 
 /* Log destination bitmap */
 #define LOG_DESTINATION_STDERR	 1