pg_basebackup: Add option to create replication slot

When requesting a particular replication slot, the new pg_basebackup
option -C/--create-slot creates it before starting to replicate from it.

Further refactor the slot creation logic to include the temporary slot
creation logic into the same function.  Add new arguments is_temporary
and preserve_wal to CreateReplicationSlot().  Print in --verbose mode
that a slot has been created.

Author: Michael Banck <michael.banck@credativ.de>

doc/src/sgml/ref/pg_basebackup.sgml

@@ -382,6 +382,18 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>-C</option></term>
+      <term><option>--create-slot</option></term>
+      <listitem>
+       <para>
+        This option causes the replication slot specified by the
+        option <literal>--slot</literal> to be created before starting the
+        backup.  In this case, an error is raised if the slot already exists.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-l <replaceable class="parameter">label</replaceable></option></term>
       <term><option>--label=<replaceable class="parameter">label</replaceable></option></term>
@@ -462,6 +474,10 @@ PostgreSQL documentation
         the server does not remove any necessary WAL data in the time between
         the end of the base backup and the start of streaming replication.
        </para>
+       <para>
+        The specified replication slot has to exist unless the
+        option <option>-C</option> is also used.
+       </para>
        <para>
         If this option is not specified and the server supports temporary
         replication slots (version 10 and later), then a temporary replication

src/bin/pg_basebackup/pg_basebackup.c

@@ -93,6 +93,8 @@ static pg_time_t last_progress_report = 0;
 static int32 maxrate = 0;		/* no limit by default */
 static char *replication_slot = NULL;
 static bool temp_replication_slot = true;
+static bool create_slot = false;
+static bool no_slot = false;
 
 static bool success = false;
 static bool made_new_pgdata = false;
@@ -346,6 +348,7 @@ usage(void)
 	printf(_("\nGeneral options:\n"));
 	printf(_("  -c, --checkpoint=fast|spread\n"
 			 "                         set fast or spread checkpointing\n"));
+	printf(_("  -C, --create-slot      create replication slot\n"));
 	printf(_("  -l, --label=LABEL      set backup label\n"));
 	printf(_("  -n, --no-clean         do not clean up after errors\n"));
 	printf(_("  -N, --no-sync          do not wait for changes to be written safely to disk\n"));
@@ -466,7 +469,6 @@ typedef struct
 	char		xlog[MAXPGPATH];	/* directory or tarfile depending on mode */
 	char	   *sysidentifier;
 	int			timeline;
-	bool		temp_slot;
 } logstreamer_param;
 
 static int
@@ -492,9 +494,6 @@ LogStreamerMain(logstreamer_param *param)
 	stream.mark_done = true;
 	stream.partial_suffix = NULL;
 	stream.replication_slot = replication_slot;
-	stream.temp_slot = param->temp_slot;
-	if (stream.temp_slot && !stream.replication_slot)
-		stream.replication_slot = psprintf("pg_basebackup_%d", (int) PQbackendPID(param->bgconn));
 
 	if (format == 'p')
 		stream.walmethod = CreateWalDirectoryMethod(param->xlog, 0, do_sync);
@@ -583,9 +582,29 @@ StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
 
 	/* Temporary replication slots are only supported in 10 and newer */
 	if (PQserverVersion(conn) < MINIMUM_VERSION_FOR_TEMP_SLOTS)
-		param->temp_slot = false;
+		temp_replication_slot = false;
+
+	/*
+	 * Create replication slot if requested
+	 */
+	if (temp_replication_slot && !replication_slot)
+		replication_slot = psprintf("pg_basebackup_%d", (int) PQbackendPID(param->bgconn));
+	if (temp_replication_slot || create_slot)
+	{
+		if (!CreateReplicationSlot(param->bgconn, replication_slot, NULL,
+								   temp_replication_slot, true, true, false))
+			disconnect_and_exit(1);
+
+		if (verbose)
+		{
+			if (temp_replication_slot)
+				fprintf(stderr, _("%s: created temporary replication slot \"%s\"\n"),
+						progname, replication_slot);
 			else
-		param->temp_slot = temp_replication_slot;
+				fprintf(stderr, _("%s: created replication slot \"%s\"\n"),
+						progname, replication_slot);
+		}
+	}
 
 	if (format == 'p')
 	{
@@ -2079,6 +2098,7 @@ main(int argc, char **argv)
 		{"pgdata", required_argument, NULL, 'D'},
 		{"format", required_argument, NULL, 'F'},
 		{"checkpoint", required_argument, NULL, 'c'},
+		{"create-slot", no_argument, NULL, 'C'},
 		{"max-rate", required_argument, NULL, 'r'},
 		{"write-recovery-conf", no_argument, NULL, 'R'},
 		{"slot", required_argument, NULL, 'S'},
@@ -2105,7 +2125,6 @@ main(int argc, char **argv)
 	int			c;
 
 	int			option_index;
-	bool		no_slot = false;
 
 	progname = get_progname(argv[0]);
 	set_pglocale_pgservice(argv[0], PG_TEXTDOMAIN("pg_basebackup"));
@@ -2127,11 +2146,14 @@ main(int argc, char **argv)
 
 	atexit(cleanup_directories_atexit);
 
-	while ((c = getopt_long(argc, argv, "D:F:r:RT:X:l:nNzZ:d:c:h:p:U:s:S:wWvP",
+	while ((c = getopt_long(argc, argv, "CD:F:r:RS:T:X:l:nNzZ:d:c:h:p:U:s:wWvP",
 							long_options, &option_index)) != -1)
 	{
 		switch (c)
 		{
+			case 'C':
+				create_slot = true;
+				break;
 			case 'D':
 				basedir = pg_strdup(optarg);
 				break;
@@ -2348,6 +2370,29 @@ main(int argc, char **argv)
 		temp_replication_slot = false;
 	}
 
+	if (create_slot)
+	{
+		if (!replication_slot)
+		{
+			fprintf(stderr,
+					_("%s: --create-slot needs a slot to be specified using --slot\n"),
+					progname);
+			fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
+					progname);
+			exit(1);
+		}
+
+		if (no_slot)
+		{
+			fprintf(stderr,
+					_("%s: --create-slot and --no-slot are incompatible options\n"),
+					progname);
+			fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
+					progname);
+			exit(1);
+		}
+	}
+
 	if (xlog_dir)
 	{
 		if (format != 'p')

src/bin/pg_basebackup/pg_receivewal.c

@@ -431,7 +431,6 @@ StreamLog(void)
 												stream.do_sync);
 	stream.partial_suffix = ".partial";
 	stream.replication_slot = replication_slot;
-	stream.temp_slot = false;
 
 	ReceiveXlogStream(conn, &stream);
 
@@ -728,7 +727,7 @@ main(int argc, char **argv)
 					_("%s: creating replication slot \"%s\"\n"),
 					progname, replication_slot);
 
-		if (!CreateReplicationSlot(conn, replication_slot, NULL, true,
+		if (!CreateReplicationSlot(conn, replication_slot, NULL, false, true, false,
 								   slot_exists_ok))
 			disconnect_and_exit(1);
 		disconnect_and_exit(0);

src/bin/pg_basebackup/pg_recvlogical.c

@@ -979,8 +979,8 @@ main(int argc, char **argv)
 					_("%s: creating replication slot \"%s\"\n"),
 					progname, replication_slot);
 
-		if (!CreateReplicationSlot(conn, replication_slot, plugin,
-								   false, slot_exists_ok))
+		if (!CreateReplicationSlot(conn, replication_slot, plugin, false,
+								   false, false, slot_exists_ok))
 			disconnect_and_exit(1);
 		startpos = InvalidXLogRecPtr;
 	}

src/bin/pg_basebackup/receivelog.c

@@ -522,24 +522,6 @@ ReceiveXlogStream(PGconn *conn, StreamCtl *stream)
 		PQclear(res);
 	}
 
-	/*
-	 * Create temporary replication slot if one is needed
-	 */
-	if (stream->temp_slot)
-	{
-		snprintf(query, sizeof(query),
-				 "CREATE_REPLICATION_SLOT \"%s\" TEMPORARY PHYSICAL RESERVE_WAL",
-				 stream->replication_slot);
-		res = PQexec(conn, query);
-		if (PQresultStatus(res) != PGRES_TUPLES_OK)
-		{
-			fprintf(stderr, _("%s: could not create temporary replication slot \"%s\": %s"),
-					progname, stream->replication_slot, PQerrorMessage(conn));
-			PQclear(res);
-			return false;
-		}
-	}
-
 	/*
 	 * initialize flush position to starting point, it's the caller's
 	 * responsibility that that's sane.

src/bin/pg_basebackup/receivelog.h

@@ -47,7 +47,6 @@ typedef struct StreamCtl
 	WalWriteMethod *walmethod;	/* How to write the WAL */
 	char	   *partial_suffix; /* Suffix appended to partially received files */
 	char	   *replication_slot;	/* Replication slot to use, or NULL */
-	bool		temp_slot;		/* Create temporary replication slot */
 } StreamCtl;
 
 

src/bin/pg_basebackup/streamutil.c

@@ -398,7 +398,8 @@ RunIdentifySystem(PGconn *conn, char **sysid, TimeLineID *starttli,
  */
 bool
 CreateReplicationSlot(PGconn *conn, const char *slot_name, const char *plugin,
-					  bool is_physical, bool slot_exists_ok)
+					  bool is_temporary, bool is_physical, bool reserve_wal,
+					  bool slot_exists_ok)
 {
 	PQExpBuffer query;
 	PGresult   *res;
@@ -410,13 +411,18 @@ CreateReplicationSlot(PGconn *conn, const char *slot_name, const char *plugin,
 	Assert(slot_name != NULL);
 
 	/* Build query */
+	appendPQExpBuffer(query, "CREATE_REPLICATION_SLOT \"%s\"", slot_name);
+	if (is_temporary)
+		appendPQExpBuffer(query, " TEMPORARY");
 	if (is_physical)
-		appendPQExpBuffer(query, "CREATE_REPLICATION_SLOT \"%s\" PHYSICAL",
-						  slot_name);
+	{
+		appendPQExpBuffer(query, " PHYSICAL");
+		if (reserve_wal)
+			appendPQExpBuffer(query, " RESERVE_WAL");
+	}
 	else
 	{
-		appendPQExpBuffer(query, "CREATE_REPLICATION_SLOT \"%s\" LOGICAL \"%s\"",
-						  slot_name, plugin);
+		appendPQExpBuffer(query, " LOGICAL \"%s\"", plugin);
 		if (PQserverVersion(conn) >= 100000)
 			/* pg_recvlogical doesn't use an exported snapshot, so suppress */
 			appendPQExpBuffer(query, " NOEXPORT_SNAPSHOT");

src/bin/pg_basebackup/streamutil.h

@@ -33,7 +33,8 @@ extern PGconn *GetConnection(void);
 
 /* Replication commands */
 extern bool CreateReplicationSlot(PGconn *conn, const char *slot_name,
-					  const char *plugin, bool is_physical,
+								  const char *plugin, bool is_temporary,
+								  bool is_physical, bool reserve_wal,
 								  bool slot_exists_ok);
 extern bool DropReplicationSlot(PGconn *conn, const char *slot_name);
 extern bool RunIdentifySystem(PGconn *conn, char **sysid,

src/bin/pg_basebackup/t/010_pg_basebackup.pl

@@ -4,7 +4,7 @@ use Cwd;
 use Config;
 use PostgresNode;
 use TestLib;
-use Test::More tests => 72;
+use Test::More tests => 78;
 
 program_help_ok('pg_basebackup');
 program_version_ok('pg_basebackup');
@@ -259,9 +259,32 @@ $node->command_fails(
 	[   'pg_basebackup',             '-D',
 		"$tempdir/backupxs_sl_fail", '-X',
 		'stream',                    '-S',
-		'slot1' ],
+		'slot0' ],
 	'pg_basebackup fails with nonexistent replication slot');
 
+$node->command_fails(
+	[   'pg_basebackup', '-D', "$tempdir/backupxs_slot", '-C' ],
+	'pg_basebackup -C fails without slot name');
+
+$node->command_fails(
+	[   'pg_basebackup', '-D', "$tempdir/backupxs_slot", '-C', '-S', 'slot0', '--no-slot' ],
+	'pg_basebackup fails with -C -S --no-slot');
+
+$node->command_ok(
+	[   'pg_basebackup', '-D', "$tempdir/backupxs_slot", '-C', '-S', 'slot0' ],
+	'pg_basebackup -C runs');
+
+is($node->safe_psql('postgres', q{SELECT slot_name FROM pg_replication_slots WHERE slot_name = 'slot0'}),
+   'slot0',
+   'replication slot was created');
+isnt($node->safe_psql('postgres', q{SELECT restart_lsn FROM pg_replication_slots WHERE slot_name = 'slot0'}),
+   '',
+   'restart LSN of new slot is not null');
+
+$node->command_fails(
+	[   'pg_basebackup', '-D', "$tempdir/backupxs_slot1", '-C', '-S', 'slot0' ],
+	'pg_basebackup fails with -C -S and a previously existing slot');
+
 $node->safe_psql('postgres',
 	q{SELECT * FROM pg_create_physical_replication_slot('slot1')});
 my $lsn = $node->safe_psql('postgres',