pg_receivewal: Add --no-sync option.

Michael Paquier, reviewed by Kuntal Ghosh and by me.  I did a little
wordsmithing on the documentation, too.

Discussion: http://postgr.es/m/CAB7nPqTuXuyEoVKcWcExh_b0uAjgWd_14KfGLrCTccBZ=VA0KA@mail.gmail.com

doc/src/sgml/ref/pg_receivewal.sgml

@@ -135,6 +135,23 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>--no-sync</option></term>
+      <listitem>
+       <para>
+        This option causes <command>pg_receivewal</command> to not force WAL
+        data to be flushed to disk.  This is faster, but means that a
+        subsequent operating system crash can leave the WAL segments corrupt.
+        Generally, this option is useful for testing but should not be used
+        when doing WAL archiving on a production deployment.
+       </para>
+
+       <para>
+        This option is incompatible with <literal>--synchronous</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-s <replaceable class="parameter">interval</replaceable></option></term>
       <term><option>--status-interval=<replaceable class="parameter">interval</replaceable></option></term>

src/bin/pg_basebackup/pg_receivewal.c

@@ -40,6 +40,7 @@ static volatile bool time_to_stop = false;
 static bool do_create_slot = false;
 static bool slot_exists_ok = false;
 static bool do_drop_slot = false;
+static bool do_sync = true;
 static bool synchronous = false;
 static char *replication_slot = NULL;
 static XLogRecPtr endpos = InvalidXLogRecPtr;
@@ -81,6 +82,7 @@ usage(void)
 	printf(_("  -E, --endpos=LSN       exit after receiving the specified LSN\n"));
 	printf(_("      --if-not-exists    do not error if slot already exists when creating a slot\n"));
 	printf(_("  -n, --no-loop          do not loop on connection lost\n"));
+	printf(_("      --no-sync          do not wait for changes to be written safely to disk\n"));
 	printf(_("  -s, --status-interval=SECS\n"
 			 "                         time between status packets sent to server (default: %d)\n"), (standby_message_timeout / 1000));
 	printf(_("  -S, --slot=SLOTNAME    replication slot to use\n"));
@@ -425,7 +427,7 @@ StreamLog(void)
 	stream.stop_socket = PGINVALID_SOCKET;
 	stream.standby_message_timeout = standby_message_timeout;
 	stream.synchronous = synchronous;
-	stream.do_sync = true;
+	stream.do_sync = do_sync;
 	stream.mark_done = false;
 	stream.walmethod = CreateWalDirectoryMethod(basedir, compresslevel,
 												stream.do_sync);
@@ -487,6 +489,7 @@ main(int argc, char **argv)
 		{"drop-slot", no_argument, NULL, 2},
 		{"if-not-exists", no_argument, NULL, 3},
 		{"synchronous", no_argument, NULL, 4},
+		{"no-sync", no_argument, NULL, 5},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -595,6 +598,9 @@ main(int argc, char **argv)
 			case 4:
 				synchronous = true;
 				break;
+			case 5:
+				do_sync = false;
+				break;
 			default:
 
 				/*
@@ -637,6 +643,14 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	if (synchronous && !do_sync)
+	{
+		fprintf(stderr, _("%s: cannot use --synchronous together with --no-sync\n"), progname);
+		fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
+				progname);
+		exit(1);
+	}
+
 	/*
 	 * Required arguments
 	 */

src/bin/pg_basebackup/t/020_pg_receivewal.pl

@@ -2,7 +2,7 @@ use strict;
 use warnings;
 use TestLib;
 use PostgresNode;
-use Test::More tests => 17;
+use Test::More tests => 18;
 
 program_help_ok('pg_receivewal');
 program_version_ok('pg_receivewal');
@@ -24,6 +24,9 @@ $primary->command_fails(
 $primary->command_fails(
 	[ 'pg_receivewal', '-D', $stream_dir, '--create-slot' ],
 	'failure if --create-slot specified without --slot');
+$primary->command_fails(
+	[ 'pg_receivewal', '-D', $stream_dir, '--synchronous', '--no-sync' ],
+	'failure if --synchronous specified with --no-sync');
 
 # Slot creation and drop
 my $slot_name = 'test';