pg_createsubscriber: Only --recovery-timeout controls the end of recovery process

It used to check if the target server is connected to the primary
server (send required WAL) to rapidly react when the process won't
succeed.  This code is not enough to guarantee that the recovery
process will complete.  There is a window between the walreceiver
shutdown and the pg_is_in_recovery() returns false that can reach
NUM_CONN_ATTEMPTS attempts and fails.

Instead, rely only on the --recovery-timeout option to give up the
process after the specified number of seconds.

This should help with buildfarm failures on slow machines.

Author: Euler Taveira <euler.taveira@enterprisedb.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Discussion: https://www.postgresql.org/message-id/776c5cac-5ef5-4001-b1bc-5b698bc0c62a%40app.fastmail.com

Author: petere

doc/src/sgml/ref/pg_createsubscriber.sgml

@@ -325,13 +325,6 @@ PostgreSQL documentation
     connections to the target server should fail.
    </para>
 
-   <para>
-    During the recovery process, if the target server disconnects from the
-    source server, <application>pg_createsubscriber</application> will check a
-    few times if the connection has been reestablished to stream the required
-    WAL.  After a few attempts, it terminates with an error.
-   </para>
-
    <para>
     Since DDL commands are not replicated by logical replication, avoid
     executing DDL commands that change the database schema while running

src/bin/pg_basebackup/pg_createsubscriber.c

@@ -1360,24 +1360,23 @@ stop_standby_server(const char *datadir)
  *
  * If recovery_timeout option is set, terminate abnormally without finishing
  * the recovery process. By default, it waits forever.
+ *
+ * XXX Is the recovery process still in progress? When recovery process has a
+ * better progress reporting mechanism, it should be added here.
  */
 static void
 wait_for_end_recovery(const char *conninfo, const struct CreateSubscriberOptions *opt)
 {
 	PGconn	   *conn;
 	int			status = POSTMASTER_STILL_STARTING;
 	int			timer = 0;
-	int			count = 0;		/* number of consecutive connection attempts */
-
-#define NUM_CONN_ATTEMPTS	10
 
 	pg_log_info("waiting for the target server to reach the consistent state");
 
 	conn = connect_database(conninfo, true);
 
 	for (;;)
 	{
-		PGresult   *res;
 		bool		in_recovery = server_is_in_recovery(conn);
 
 		/*
@@ -1391,28 +1390,6 @@ wait_for_end_recovery(const char *conninfo, const struct CreateSubscriberOptions
 			break;
 		}
 
-		/*
-		 * If it is still in recovery, make sure the target server is
-		 * connected to the primary so it can receive the required WAL to
-		 * finish the recovery process. If it is disconnected try
-		 * NUM_CONN_ATTEMPTS in a row and bail out if not succeed.
-		 */
-		res = PQexec(conn,
-					 "SELECT 1 FROM pg_catalog.pg_stat_wal_receiver");
-		if (PQntuples(res) == 0)
-		{
-			if (++count > NUM_CONN_ATTEMPTS)
-			{
-				stop_standby_server(subscriber_dir);
-				pg_log_error("standby server disconnected from the primary");
-				break;
-			}
-		}
-		else
-			count = 0;			/* reset counter if it connects again */
-
-		PQclear(res);
-
 		/* Bail out after recovery_timeout seconds if this option is set */
 		if (opt->recovery_timeout > 0 && timer >= opt->recovery_timeout)
 		{

src/bin/pg_basebackup/t/040_pg_createsubscriber.pl

@@ -264,6 +264,7 @@
 command_ok(
 	[
 		'pg_createsubscriber', '--verbose',
+		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
 		'--dry-run', '--pgdata',
 		$node_s->data_dir, '--publisher-server',
 		$node_p->connstr('pg1'), '--socket-directory',
@@ -301,6 +302,7 @@
 command_ok(
 	[
 		'pg_createsubscriber', '--verbose',
+		'--recovery-timeout', "$PostgreSQL::Test::Utils::timeout_default",
 		'--verbose', '--pgdata',
 		$node_s->data_dir, '--publisher-server',
 		$node_p->connstr('pg1'), '--socket-directory',