Allow enabling two-phase option via replication protocol.

Extend the replication command CREATE_REPLICATION_SLOT to support the
TWO_PHASE option. This will allow decoding commands like PREPARE
TRANSACTION, COMMIT PREPARED and ROLLBACK PREPARED for slots created with
this option. The decoding of the transaction happens at prepare command.

This patch also adds support of two-phase in pg_recvlogical via a new
option --two-phase.

This option will also be used by future patches that allow streaming of
transactions at prepare time for built-in logical replication. With this,
the out-of-core logical replication solutions can enable replication of
two-phase transactions via replication protocol.

Author: Ajin Cherian
Reviewed-By: Jeff Davis, Vignesh C, Amit Kapila
Discussion:
https://postgr.es/m/02DA5F5E-CECE-4D9C-8B4B-418077E2C010@postgrespro.ru
https://postgr.es/m/64b9f783c6e125f18f88fbc0c0234e34e71d8639.camel@j-davis.com

Author: Amit Kapila

doc/src/sgml/logicaldecoding.sgml

@@ -144,16 +144,19 @@ postgres=# SELECT pg_drop_replication_slot('regression_slot');
 </programlisting>
 
    <para>
-    The following example shows how logical decoding is controlled over the
+    The following examples shows how logical decoding is controlled over the
     streaming replication protocol, using the
     program <xref linkend="app-pgrecvlogical"/> included in the PostgreSQL
     distribution.  This requires that client authentication is set up to allow
     replication connections
     (see <xref linkend="streaming-replication-authentication"/>) and
     that <varname>max_wal_senders</varname> is set sufficiently high to allow
-    an additional connection.
+    an additional connection.  The second example shows how to stream two-phase
+    transactions.  Before you use two-phase commands, you must set
+    <xref linkend="guc-max-prepared-transactions"/> to atleast 1.
    </para>
 <programlisting>
+Example 1:
 $ pg_recvlogical -d postgres --slot=test --create-slot
 $ pg_recvlogical -d postgres --slot=test --start -f -
 <keycombo action="simul"><keycap>Control</keycap><keycap>Z</keycap></keycombo>
@@ -164,6 +167,22 @@ table public.data: INSERT: id[integer]:4 data[text]:'4'
 COMMIT 693
 <keycombo action="simul"><keycap>Control</keycap><keycap>C</keycap></keycombo>
 $ pg_recvlogical -d postgres --slot=test --drop-slot
+
+Example 2:
+$ pg_recvlogical -d postgres --slot=test --create-slot --two-phase
+$ pg_recvlogical -d postgres --slot=test --start -f -
+<keycombo action="simul"><keycap>Control</keycap><keycap>Z</keycap></keycombo>
+$ psql -d postgres -c "BEGIN;INSERT INTO data(data) VALUES('5');PREPARE TRANSACTION 'test';"
+$ fg
+BEGIN 694
+table public.data: INSERT: id[integer]:5 data[text]:'5'
+PREPARE TRANSACTION 'test', txid 694
+<keycombo action="simul"><keycap>Control</keycap><keycap>Z</keycap></keycombo>
+$ psql -d postgres -c "COMMIT PREPARED 'test';"
+$ fg
+COMMIT PREPARED 'test', txid 694
+<keycombo action="simul"><keycap>Control</keycap><keycap>C</keycap></keycombo>
+$ pg_recvlogical -d postgres --slot=test --drop-slot
 </programlisting>
 
   <para>

doc/src/sgml/protocol.sgml

@@ -1914,7 +1914,7 @@ The commands accepted in replication mode are:
   </varlistentry>
 
   <varlistentry id="protocol-replication-create-slot" xreflabel="CREATE_REPLICATION_SLOT">
-   <term><literal>CREATE_REPLICATION_SLOT</literal> <replaceable class="parameter">slot_name</replaceable> [ <literal>TEMPORARY</literal> ] { <literal>PHYSICAL</literal> [ <literal>RESERVE_WAL</literal> ] | <literal>LOGICAL</literal> <replaceable class="parameter">output_plugin</replaceable> [ <literal>EXPORT_SNAPSHOT</literal> | <literal>NOEXPORT_SNAPSHOT</literal> | <literal>USE_SNAPSHOT</literal> ] }
+   <term><literal>CREATE_REPLICATION_SLOT</literal> <replaceable class="parameter">slot_name</replaceable> [ <literal>TEMPORARY</literal> ] { <literal>PHYSICAL</literal> [ <literal>RESERVE_WAL</literal> ] | <literal>LOGICAL</literal> <replaceable class="parameter">output_plugin</replaceable> [ <literal>EXPORT_SNAPSHOT</literal> | <literal>NOEXPORT_SNAPSHOT</literal> | <literal>USE_SNAPSHOT</literal> | <literal>TWO_PHASE</literal> ] }
      <indexterm><primary>CREATE_REPLICATION_SLOT</primary></indexterm>
     </term>
     <listitem>
@@ -1955,6 +1955,20 @@ The commands accepted in replication mode are:
        </listitem>
       </varlistentry>
 
+      <varlistentry>
+       <term><literal>TWO_PHASE</literal></term>
+       <listitem>
+        <para>
+         Specify that this logical replication slot supports decoding of two-phase
+         transactions. With this option, two-phase commands like
+         <literal>PREPARE TRANSACTION</literal>, <literal>COMMIT PREPARED</literal>
+         and <literal>ROLLBACK PREPARED</literal> are decoded and transmitted.
+         The transaction will be decoded and transmitted at
+         <literal>PREPARE TRANSACTION</literal> time.
+        </para>
+       </listitem>
+      </varlistentry>
+
       <varlistentry>
        <term><literal>RESERVE_WAL</literal></term>
        <listitem>

doc/src/sgml/ref/pg_recvlogical.sgml

@@ -65,6 +65,11 @@ PostgreSQL documentation
         <option>--plugin</option>, for the database specified
         by <option>--dbname</option>.
        </para>
+
+       <para>
+        The <option>--two-phase</option> can be specified with
+        <option>--create-slot</option> to enable two-phase decoding.
+       </para>
       </listitem>
      </varlistentry>
 
@@ -256,6 +261,17 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+       <term><option>-t</option></term>
+       <term><option>--two-phase</option></term>
+       <listitem>
+       <para>
+        Enables two-phase decoding. This option should only be specified with
+        <option>--create-slot</option>
+       </para>
+       </listitem>
+     </varlistentry>
+
      <varlistentry>
        <term><option>-v</option></term>
        <term><option>--verbose</option></term>

src/backend/replication/repl_gram.y

@@ -84,6 +84,7 @@ static SQLCmd *make_sqlcmd(void);
 %token K_SLOT
 %token K_RESERVE_WAL
 %token K_TEMPORARY
+%token K_TWO_PHASE
 %token K_EXPORT_SNAPSHOT
 %token K_NOEXPORT_SNAPSHOT
 %token K_USE_SNAPSHOT
@@ -283,6 +284,11 @@ create_slot_opt:
 				  $$ = makeDefElem("reserve_wal",
 								   (Node *)makeInteger(true), -1);
 				}
+			| K_TWO_PHASE
+				{
+				  $$ = makeDefElem("two_phase",
+								   (Node *)makeInteger(true), -1);
+				}
 			;
 
 /* DROP_REPLICATION_SLOT slot */

src/backend/replication/repl_scanner.l

@@ -103,6 +103,7 @@ RESERVE_WAL			{ return K_RESERVE_WAL; }
 LOGICAL				{ return K_LOGICAL; }
 SLOT				{ return K_SLOT; }
 TEMPORARY			{ return K_TEMPORARY; }
+TWO_PHASE			{ return K_TWO_PHASE; }
 EXPORT_SNAPSHOT		{ return K_EXPORT_SNAPSHOT; }
 NOEXPORT_SNAPSHOT	{ return K_NOEXPORT_SNAPSHOT; }
 USE_SNAPSHOT		{ return K_USE_SNAPSHOT; }

src/backend/replication/walsender.c

@@ -863,11 +863,13 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 static void
 parseCreateReplSlotOptions(CreateReplicationSlotCmd *cmd,
 						   bool *reserve_wal,
-						   CRSSnapshotAction *snapshot_action)
+						   CRSSnapshotAction *snapshot_action,
+						   bool *two_phase)
 {
 	ListCell   *lc;
 	bool		snapshot_action_given = false;
 	bool		reserve_wal_given = false;
+	bool		two_phase_given = false;
 
 	/* Parse options */
 	foreach(lc, cmd->options)
@@ -905,6 +907,15 @@ parseCreateReplSlotOptions(CreateReplicationSlotCmd *cmd,
 			reserve_wal_given = true;
 			*reserve_wal = true;
 		}
+		else if (strcmp(defel->defname, "two_phase") == 0)
+		{
+			if (two_phase_given || cmd->kind != REPLICATION_KIND_LOGICAL)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			two_phase_given = true;
+			*two_phase = true;
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -920,6 +931,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	char		xloc[MAXFNAMELEN];
 	char	   *slot_name;
 	bool		reserve_wal = false;
+	bool		two_phase = false;
 	CRSSnapshotAction snapshot_action = CRS_EXPORT_SNAPSHOT;
 	DestReceiver *dest;
 	TupOutputState *tstate;
@@ -929,7 +941,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 	Assert(!MyReplicationSlot);
 
-	parseCreateReplSlotOptions(cmd, &reserve_wal, &snapshot_action);
+	parseCreateReplSlotOptions(cmd, &reserve_wal, &snapshot_action, &two_phase);
 
 	/* setup state for WalSndSegmentOpen */
 	sendTimeLineIsHistoric = false;
@@ -954,7 +966,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  false);
+							  two_phase);
 	}
 
 	if (cmd->kind == REPLICATION_KIND_LOGICAL)

src/bin/pg_basebackup/pg_basebackup.c

@@ -646,7 +646,7 @@ StartLogStreamer(char *startpos, uint32 timeline, char *sysidentifier)
 	if (temp_replication_slot || create_slot)
 	{
 		if (!CreateReplicationSlot(param->bgconn, replication_slot, NULL,
-								   temp_replication_slot, true, true, false))
+								   temp_replication_slot, true, true, false, false))
 			exit(1);
 
 		if (verbose)

src/bin/pg_basebackup/pg_receivewal.c

@@ -741,7 +741,7 @@ main(int argc, char **argv)
 			pg_log_info("creating replication slot \"%s\"", replication_slot);
 
 		if (!CreateReplicationSlot(conn, replication_slot, NULL, false, true, false,
-								   slot_exists_ok))
+								   slot_exists_ok, false))
 			exit(1);
 		exit(0);
 	}

src/bin/pg_basebackup/pg_recvlogical.c

@@ -35,6 +35,7 @@
 /* Global Options */
 static char *outfile = NULL;
 static int	verbose = 0;
+static bool two_phase = false;
 static int	noloop = 0;
 static int	standby_message_timeout = 10 * 1000;	/* 10 sec = default */
 static int	fsync_interval = 10 * 1000; /* 10 sec = default */
@@ -93,6 +94,7 @@ usage(void)
 	printf(_("  -s, --status-interval=SECS\n"
 			 "                         time between status packets sent to server (default: %d)\n"), (standby_message_timeout / 1000));
 	printf(_("  -S, --slot=SLOTNAME    name of the logical replication slot\n"));
+	printf(_("  -t, --two-phase        enable two-phase decoding when creating a slot\n"));
 	printf(_("  -v, --verbose          output verbose messages\n"));
 	printf(_("  -V, --version          output version information, then exit\n"));
 	printf(_("  -?, --help             show this help, then exit\n"));
@@ -678,6 +680,7 @@ main(int argc, char **argv)
 		{"fsync-interval", required_argument, NULL, 'F'},
 		{"no-loop", no_argument, NULL, 'n'},
 		{"verbose", no_argument, NULL, 'v'},
+		{"two-phase", no_argument, NULL, 't'},
 		{"version", no_argument, NULL, 'V'},
 		{"help", no_argument, NULL, '?'},
 /* connection options */
@@ -726,7 +729,7 @@ main(int argc, char **argv)
 		}
 	}
 
-	while ((c = getopt_long(argc, argv, "E:f:F:nvd:h:p:U:wWI:o:P:s:S:",
+	while ((c = getopt_long(argc, argv, "E:f:F:nvtd:h:p:U:wWI:o:P:s:S:",
 							long_options, &option_index)) != -1)
 	{
 		switch (c)
@@ -749,6 +752,9 @@ main(int argc, char **argv)
 			case 'v':
 				verbose++;
 				break;
+			case 't':
+				two_phase = true;
+				break;
 /* connection options */
 			case 'd':
 				dbname = pg_strdup(optarg);
@@ -920,6 +926,15 @@ main(int argc, char **argv)
 		exit(1);
 	}
 
+	if (two_phase && !do_create_slot)
+	{
+		pg_log_error("--two-phase may only be specified with --create-slot");
+		fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
+				progname);
+		exit(1);
+	}
+
+
 #ifndef WIN32
 	pqsignal(SIGINT, sigint_handler);
 	pqsignal(SIGHUP, sighup_handler);
@@ -976,7 +991,7 @@ main(int argc, char **argv)
 			pg_log_info("creating replication slot \"%s\"", replication_slot);
 
 		if (!CreateReplicationSlot(conn, replication_slot, plugin, false,
-								   false, false, slot_exists_ok))
+								   false, false, slot_exists_ok, two_phase))
 			exit(1);
 		startpos = InvalidXLogRecPtr;
 	}

src/bin/pg_basebackup/streamutil.c

@@ -486,7 +486,7 @@ RunIdentifySystem(PGconn *conn, char **sysid, TimeLineID *starttli,
 bool
 CreateReplicationSlot(PGconn *conn, const char *slot_name, const char *plugin,
 					  bool is_temporary, bool is_physical, bool reserve_wal,
-					  bool slot_exists_ok)
+					  bool slot_exists_ok, bool two_phase)
 {
 	PQExpBuffer query;
 	PGresult   *res;
@@ -495,6 +495,7 @@ CreateReplicationSlot(PGconn *conn, const char *slot_name, const char *plugin,
 
 	Assert((is_physical && plugin == NULL) ||
 		   (!is_physical && plugin != NULL));
+	Assert(!(two_phase && is_physical));
 	Assert(slot_name != NULL);
 
 	/* Build query */
@@ -510,6 +511,9 @@ CreateReplicationSlot(PGconn *conn, const char *slot_name, const char *plugin,
 	else
 	{
 		appendPQExpBuffer(query, " LOGICAL \"%s\"", plugin);
+		if (two_phase && PQserverVersion(conn) >= 150000)
+			appendPQExpBufferStr(query, " TWO_PHASE");
+
 		if (PQserverVersion(conn) >= 100000)
 			/* pg_recvlogical doesn't use an exported snapshot, so suppress */
 			appendPQExpBufferStr(query, " NOEXPORT_SNAPSHOT");

src/bin/pg_basebackup/streamutil.h

@@ -34,7 +34,7 @@ extern PGconn *GetConnection(void);
 extern bool CreateReplicationSlot(PGconn *conn, const char *slot_name,
 								  const char *plugin, bool is_temporary,
 								  bool is_physical, bool reserve_wal,
-								  bool slot_exists_ok);
+								  bool slot_exists_ok, bool two_phase);
 extern bool DropReplicationSlot(PGconn *conn, const char *slot_name);
 extern bool RunIdentifySystem(PGconn *conn, char **sysid,
 							  TimeLineID *starttli,

src/bin/pg_basebackup/t/030_pg_recvlogical.pl

@@ -5,7 +5,7 @@
 use warnings;
 use TestLib;
 use PostgresNode;
-use Test::More tests => 15;
+use Test::More tests => 20;
 
 program_help_ok('pg_recvlogical');
 program_version_ok('pg_recvlogical');
@@ -22,6 +22,7 @@
 max_wal_senders = 4
 log_min_messages = 'debug1'
 log_error_verbosity = verbose
+max_prepared_transactions = 10
 });
 $node->dump_info;
 $node->start;
@@ -63,3 +64,45 @@
 		'--start', '--endpos', "$nextlsn", '--no-loop', '-f', '-'
 	],
 	'replayed a transaction');
+
+$node->command_ok(
+	[
+		'pg_recvlogical',           '-S',
+		'test',                     '-d',
+		$node->connstr('postgres'), '--drop-slot'
+	],
+	'slot dropped');
+
+#test with two-phase option enabled
+$node->command_ok(
+	[
+		'pg_recvlogical',           '-S',
+		'test',                     '-d',
+		$node->connstr('postgres'), '--create-slot', '--two-phase'
+	],
+	'slot with two-phase created');
+
+$slot = $node->slot('test');
+isnt($slot->{'restart_lsn'}, '', 'restart lsn is defined for new slot');
+
+$node->safe_psql('postgres',
+	"BEGIN; INSERT INTO test_table values (11); PREPARE TRANSACTION 'test'");
+$node->safe_psql('postgres',
+	"COMMIT PREPARED 'test'");
+$nextlsn =
+  $node->safe_psql('postgres', 'SELECT pg_current_wal_insert_lsn()');
+chomp($nextlsn);
+
+$node->command_fails(
+	[
+		'pg_recvlogical', '-S', 'test', '-d', $node->connstr('postgres'),
+		'--start', '--endpos', "$nextlsn", '--two-phase', '--no-loop', '-f', '-'
+	],
+	'incorrect usage');
+
+$node->command_ok(
+	[
+		'pg_recvlogical', '-S', 'test', '-d', $node->connstr('postgres'),
+		'--start', '--endpos', "$nextlsn", '--no-loop', '-f', '-'
+	],
+	'replayed a two-phase transaction');