Implement "pg_ctl logrotate" command

Currently there are two ways to trigger log rotation in logging collector
process: call pg_rotate_logfile() SQL-function or send SIGUSR1 signal directly
to logging collector process.  However, it's nice to have more suitable way
for external tools to do that, which wouldn't require SQL connection or
knowledge of logging collector pid.  This commit implements triggering log
rotation by "pg_ctl logrotate" command.

Discussion: https://postgr.es/m/20180416.115435.28153375.horiguchi.kyotaro%40lab.ntt.co.jp
Author: Kyotaro Horiguchi, Alexander Kuzmenkov, Alexander Korotkov

doc/src/sgml/maintenance.sgml

@@ -932,8 +932,8 @@ analyze threshold = analyze base threshold + analyze scale factor * number of tu
    program if you have one that you are already using with other
    server software. For example, the <application>rotatelogs</application>
    tool included in the <productname>Apache</productname> distribution
-   can be used with <productname>PostgreSQL</productname>.  To do this,
-   just pipe the server's
+   can be used with <productname>PostgreSQL</productname>.  One way to
+   do this is to pipe the server's
    <systemitem>stderr</systemitem> output to the desired program.
    If you start the server with
    <command>pg_ctl</command>, then <systemitem>stderr</systemitem>
@@ -945,6 +945,36 @@ pg_ctl start | rotatelogs /var/log/pgsql_log 86400
 </programlisting>
   </para>
 
+  <para>
+   You can combine these approaches by setting up <application>logrotate</application>
+   to collect log files produced by <productname>PostgreSQL</productname> built-in
+   logging collector.  In this case, the logging collector defines the names and
+   location of the log files, while <application>logrotate</application>
+   periodically archives these files.  When initiating log rotation,
+   <application>logrotate</application> must ensure that the application
+   sends further output to the new file.  This is commonly done with a
+   <literal>postrotate</literal> script that sends a <literal>SIGHUP</literal>
+   signal to the application, which then reopens the log file.
+   In <productname>PostgreSQL</productname>, you can run <command>pg_ctl</command>
+   with the <literal>logrotate</literal> option instead.  When the server receives
+   this command, the server either switches to a new log file or reopens the
+   existing file, depending on the logging configuration
+   (see <xref linkend="runtime-config-logging-where"/>).
+  </para>
+
+  <note>
+   <para>
+    When using static log file names, the server might fail to reopen the log
+    file if the max open file limit is reached or a file table overflow occurs.
+    In this case, log messages are sent to the old log file until a
+    successful log rotation. If <application>logrotate</application> is
+    configured to compress the log file and delete it, the server may lose
+    the messages logged in this timeframe. To avoid this issue, you can
+    configure the logging collector to dynamically assign log file names
+    and use a <literal>prerotate</literal> script to ignore open log files.
+    </para>
+  </note>
+
   <para>
    Another production-grade approach to managing log output is to
    send it to <application>syslog</application> and let

doc/src/sgml/ref/pg_ctl-ref.sgml

@@ -97,6 +97,13 @@ PostgreSQL documentation
    <arg choice="opt"><option>-s</option></arg>
   </cmdsynopsis>
 
+  <cmdsynopsis>
+   <command>pg_ctl</command>
+   <arg choice="plain"><option>logrotate</option></arg>
+   <arg choice="opt"><option>-D</option> <replaceable>datadir</replaceable></arg>
+   <arg choice="opt"><option>-s</option></arg>
+  </cmdsynopsis>
+
   <cmdsynopsis>
    <command>pg_ctl</command>
    <arg choice="plain"><option>kill</option></arg>
@@ -226,6 +233,12 @@ PostgreSQL documentation
    and begin read-write operations.
   </para>
 
+  <para>
+   <option>logrotate</option> mode rotates the server log file.
+   For details on how to use this mode with external log rotation tools, see
+   <xref linkend="logfile-maintenance"/>.
+  </para>
+
   <para>
    <option>kill</option> mode sends a signal to a specified process.
    This is primarily valuable on <productname>Microsoft Windows</productname>

src/backend/postmaster/postmaster.c

@@ -1268,6 +1268,9 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	RemovePromoteSignalFiles();
 
+	/* Do the same for logrotate signal file */
+	RemoveLogrotateSignalFiles();
+
 	/* Remove any outdated file holding the current log filenames. */
 	if (unlink(LOG_METAINFO_DATAFILE) < 0 && errno != ENOENT)
 		ereport(LOG,
@@ -5100,11 +5103,18 @@ sigusr1_handler(SIGNAL_ARGS)
 		signal_child(PgArchPID, SIGUSR1);
 	}
 
-	if (CheckPostmasterSignal(PMSIGNAL_ROTATE_LOGFILE) &&
-		SysLoggerPID != 0)
+	/* Tell syslogger to rotate logfile if requested */
+	if (SysLoggerPID != 0)
+	{
+		if (CheckLogrotateSignal())
 		{
-		/* Tell syslogger to rotate logfile */
 			signal_child(SysLoggerPID, SIGUSR1);
+			RemoveLogrotateSignalFiles();
+		}
+		else if (CheckPostmasterSignal(PMSIGNAL_ROTATE_LOGFILE))
+		{
+			signal_child(SysLoggerPID, SIGUSR1);
+		}
 	}
 
 	if (CheckPostmasterSignal(PMSIGNAL_START_AUTOVAC_LAUNCHER) &&

src/backend/postmaster/syslogger.c

@@ -57,6 +57,9 @@
  */
 #define READ_BUF_SIZE (2 * PIPE_CHUNK_SIZE)
 
+/* Log rotation signal file path, relative to $PGDATA */
+#define LOGROTATE_SIGNAL_FILE	"logrotate"
+
 
 /*
  * GUC parameters.  Logging_collector cannot be changed after postmaster
@@ -405,7 +408,7 @@ SysLoggerMain(int argc, char *argv[])
 		{
 			/*
 			 * Force rotation when both values are zero. It means the request
-			 * was sent by pg_rotate_logfile.
+			 * was sent by pg_rotate_logfile() or "pg_ctl logrotate".
 			 */
 			if (!time_based_rotation && size_rotation_for == 0)
 				size_rotation_for = LOG_DESTINATION_STDERR | LOG_DESTINATION_CSVLOG;
@@ -1506,6 +1509,30 @@ update_metainfo_datafile(void)
  * --------------------------------
  */
 
+/*
+ * Check to see if a log rotation request has arrived.  Should be
+ * called by postmaster after receiving SIGUSR1.
+ */
+bool
+CheckLogrotateSignal(void)
+{
+	struct stat stat_buf;
+
+	if (stat(LOGROTATE_SIGNAL_FILE, &stat_buf) == 0)
+		return true;
+
+	return false;
+}
+
+/*
+ * Remove the file signaling a log rotateion request.
+ */
+void
+RemoveLogrotateSignalFiles(void)
+{
+	unlink(LOGROTATE_SIGNAL_FILE);
+}
+
 /* SIGHUP: set flag to reload config file */
 static void
 sigHupHandler(SIGNAL_ARGS)

src/bin/pg_ctl/pg_ctl.c

@@ -61,6 +61,7 @@ typedef enum
 	RELOAD_COMMAND,
 	STATUS_COMMAND,
 	PROMOTE_COMMAND,
+	LOGROTATE_COMMAND,
 	KILL_COMMAND,
 	REGISTER_COMMAND,
 	UNREGISTER_COMMAND,
@@ -100,6 +101,7 @@ static char version_file[MAXPGPATH];
 static char pid_file[MAXPGPATH];
 static char backup_file[MAXPGPATH];
 static char promote_file[MAXPGPATH];
+static char logrotate_file[MAXPGPATH];
 
 #ifdef WIN32
 static DWORD pgctl_start_type = SERVICE_AUTO_START;
@@ -125,6 +127,7 @@ static void do_restart(void);
 static void do_reload(void);
 static void do_status(void);
 static void do_promote(void);
+static void do_logrotate(void);
 static void do_kill(pgpid_t pid);
 static void print_msg(const char *msg);
 static void adjust_data_dir(void);
@@ -1171,6 +1174,62 @@ do_promote(void)
 		print_msg(_("server promoting\n"));
 }
 
+/*
+ * log rotate
+ */
+
+static void
+do_logrotate(void)
+{
+	FILE	   *logrotatefile;
+	pgpid_t		pid;
+
+	pid = get_pgpid(false);
+
+	if (pid == 0)				/* no pid file */
+	{
+		write_stderr(_("%s: PID file \"%s\" does not exist\n"), progname, pid_file);
+		write_stderr(_("Is server running?\n"));
+		exit(1);
+	}
+	else if (pid < 0)			/* standalone backend, not postmaster */
+	{
+		pid = -pid;
+		write_stderr(_("%s: cannot rotate log file; "
+					   "single-user server is running (PID: %ld)\n"),
+					 progname, pid);
+		exit(1);
+	}
+
+	snprintf(logrotate_file, MAXPGPATH, "%s/logrotate", pg_data);
+
+	if ((logrotatefile = fopen(logrotate_file, "w")) == NULL)
+	{
+		write_stderr(_("%s: could not create log rotation signal file \"%s\": %s\n"),
+					 progname, logrotate_file, strerror(errno));
+		exit(1);
+	}
+	if (fclose(logrotatefile))
+	{
+		write_stderr(_("%s: could not write log rotation signal file \"%s\": %s\n"),
+					 progname, logrotate_file, strerror(errno));
+		exit(1);
+	}
+
+	sig = SIGUSR1;
+	if (kill((pid_t) pid, sig) != 0)
+	{
+		write_stderr(_("%s: could not send log rotation signal (PID: %ld): %s\n"),
+					 progname, pid, strerror(errno));
+		if (unlink(logrotate_file) != 0)
+			write_stderr(_("%s: could not remove log rotation signal file \"%s\": %s\n"),
+						 progname, logrotate_file, strerror(errno));
+		exit(1);
+	}
+
+	print_msg(_("server signaled to rotate log file\n"));
+}
+
 
 /*
  *	utility routines
@@ -1921,6 +1980,7 @@ do_help(void)
 	printf(_("  %s reload     [-D DATADIR] [-s]\n"), progname);
 	printf(_("  %s status     [-D DATADIR]\n"), progname);
 	printf(_("  %s promote    [-D DATADIR] [-W] [-t SECS] [-s]\n"), progname);
+	printf(_("  %s logrotate  [-D DATADIR] [-s]\n"), progname);
 	printf(_("  %s kill       SIGNALNAME PID\n"), progname);
 #ifdef WIN32
 	printf(_("  %s register   [-D DATADIR] [-N SERVICENAME] [-U USERNAME] [-P PASSWORD]\n"
@@ -2337,6 +2397,8 @@ main(int argc, char **argv)
 				ctl_command = STATUS_COMMAND;
 			else if (strcmp(argv[optind], "promote") == 0)
 				ctl_command = PROMOTE_COMMAND;
+			else if (strcmp(argv[optind], "logrotate") == 0)
+				ctl_command = LOGROTATE_COMMAND;
 			else if (strcmp(argv[optind], "kill") == 0)
 			{
 				if (argc - optind < 3)
@@ -2443,6 +2505,9 @@ main(int argc, char **argv)
 		case PROMOTE_COMMAND:
 			do_promote();
 			break;
+		case LOGROTATE_COMMAND:
+			do_logrotate();
+			break;
 		case KILL_COMMAND:
 			do_kill(killproc);
 			break;

src/bin/pg_ctl/t/004_logrotate.pl

+use strict;
+use warnings;
+
+use PostgresNode;
+use TestLib;
+use Test::More tests => 1;
+use Time::HiRes qw(usleep);
+
+my $tempdir = TestLib::tempdir;
+
+my $node = get_new_node('primary');
+$node->init(allows_streaming => 1);
+$node->append_conf(
+	'postgresql.conf', qq(
+logging_collector = on
+log_directory = 'log'
+log_filename = 'postgresql.log'
+));
+
+$node->start();
+
+# Rename log file and rotate log.  Then log file should appear again.
+
+my $logfile = $node->data_dir . '/log/postgresql.log';
+my $old_logfile = $node->data_dir . '/log/postgresql.old';
+rename($logfile, $old_logfile);
+
+$node->logrotate();
+
+# pg_ctl logrotate doesn't wait until rotation request being completed.  So
+# we have to wait some time until log file appears.
+my $attempts = 0;
+my $max_attempts = 180 * 10;
+while (not -e $logfile and $attempts < $max_attempts)
+{
+	usleep(100_000);
+	$attempts++;
+}
+
+ok(-e $logfile, "log file exists");
+
+$node->stop();

src/include/postmaster/syslogger.h

@@ -87,6 +87,9 @@ extern void write_syslogger_file(const char *buffer, int count, int dest);
 extern void SysLoggerMain(int argc, char *argv[]) pg_attribute_noreturn();
 #endif
 
+extern bool CheckLogrotateSignal(void);
+extern void RemoveLogrotateSignalFiles(void);
+
 /*
  * Name of files saving meta-data information about the log
  * files currently in use by the syslogger

src/test/perl/PostgresNode.pm

@@ -804,6 +804,27 @@ sub promote
 	return;
 }
 
+=pod
+
+=item $node->logrotate()
+
+Wrapper for pg_ctl logrotate
+
+=cut
+
+sub logrotate
+{
+	my ($self)  = @_;
+	my $port    = $self->port;
+	my $pgdata  = $self->data_dir;
+	my $logfile = $self->logfile;
+	my $name    = $self->name;
+	print "### Rotating log in node \"$name\"\n";
+	TestLib::system_or_bail('pg_ctl', '-D', $pgdata, '-l', $logfile,
+		'logrotate');
+	return;
+}
+
 # Internal routine to enable streaming replication on a standby node.
 sub enable_streaming
 {