diff --git a/samples/Z0DAN/zodan.sql b/samples/Z0DAN/zodan.sql
index 38baba40..bd7345e3 100644
--- a/samples/Z0DAN/zodan.sql
+++ b/samples/Z0DAN/zodan.sql
@@ -1531,6 +1531,40 @@ BEGIN
         END IF;
     END;
 
+    -- Check: all nodes, included in the cluster, have only enabled subscriptions.
+	--
+	-- Connect to each node in the cluster and pass through the spock.subscription
+	-- table to check subscriptions statuses. Using it we try to avoid cases
+	-- when somewhere in the middle a crash or disconnection happens that may
+	-- be aggravated by add_node.
+    DECLARE
+		status_rec     record;
+		dsn_rec        record;
+		dsns_sql       text;
+		sub_status_sql text;
+    BEGIN
+        dsns_sql := 'SELECT if_dsn,node_name
+					 FROM spock.node JOIN spock.node_interface
+					 ON (if_nodeid = node_id)
+					 WHERE node_id NOT IN (SELECT node_id FROM spock.local_node)';
+		sub_status_sql := 'SELECT sub_name, sub_enabled FROM spock.subscription';
+
+        FOR dsn_rec IN SELECT * FROM dblink(src_dsn, dsns_sql)
+													AS t(dsn text, node name)
+		LOOP
+			FOR status_rec IN SELECT * FROM dblink(dsn_rec.dsn, sub_status_sql)
+													AS t(name text, status text)
+			LOOP
+			    IF status_rec.status != 't' THEN
+                    RAISE EXCEPTION '    [FAILED] %', rpad('Node ' || dsn_rec.node || ' has disabled subscription ' || status_rec.name, 60, ' ');
+                ELSIF verb THEN
+                    RAISE NOTICE '    OK: %', rpad('Node with DSN ' || dsn_rec.dsn || ' has enabled subscription ' || status_rec.name, 120, ' ');
+                END IF;
+			END LOOP;
+        END LOOP;
+		RAISE NOTICE '    OK: %', rpad('Checking each Spock node has only active subscriptions', 120, ' ');
+    END;
+
     -- Validating new node prerequisites
     SELECT count(*) INTO new_exists FROM spock.node WHERE node_name = new_node_name;
     IF new_exists > 0 THEN
@@ -2317,8 +2351,7 @@ BEGIN
         RAISE NOTICE '    OK: %', rpad('Waiting for sync event from ' || src_node_name || ' on new node ' || new_node_name || '...', 120, ' ');
     EXCEPTION
         WHEN OTHERS THEN
-            RAISE NOTICE '    ✗ %', rpad('Unable to wait for sync event from ' || src_node_name || ' on new node ' || new_node_name || ' (error: ' || SQLERRM || ')', 120, ' ');
-            RAISE;
+            RAISE EXCEPTION '    ✗ %', rpad('Unable to wait for sync event from ' || src_node_name || ' on new node ' || new_node_name || ' (error: ' || SQLERRM || ')', 120, ' ');
     END;
 END;
 $$;
diff --git a/sql/spock--6.0.0-devel.sql b/sql/spock--6.0.0-devel.sql
index 1ad9a9a8..0732398a 100644
--- a/sql/spock--6.0.0-devel.sql
+++ b/sql/spock--6.0.0-devel.sql
@@ -414,6 +414,17 @@ BEGIN
 	target_id := node_id FROM spock.node_info();
 
 	WHILE true LOOP
+		-- If an unresolvable issue occurs with the apply worker, the LR
+		-- progress gets stuck, and we need to check the subscription's state
+		-- carefully.
+		IF NOT EXISTS (SELECT * FROM spock.subscription
+					  WHERE sub_origin = origin_id AND
+							sub_target = target_id AND
+							sub_enabled = true) THEN
+			RAISE EXCEPTION 'Replication % => % does not have any enabled subscription yet',
+							origin_id, target_id;
+		END IF;
+
 		SELECT INTO progress_lsn remote_commit_lsn
 			FROM spock.progress
 			WHERE node_id = target_id AND remote_node_id = origin_id;
@@ -452,6 +463,17 @@ BEGIN
 	target_id := node_id FROM spock.node_info();
 
 	WHILE true LOOP
+		-- If an unresolvable issue occurs with the apply worker, the LR
+		-- progress gets stuck, and we need to check the subscription's state
+		-- carefully.
+		IF NOT EXISTS (SELECT * FROM spock.subscription
+					  WHERE sub_origin = origin_id AND
+							sub_target = target_id AND
+							sub_enabled = true) THEN
+			RAISE EXCEPTION 'Replication % => % does not have any enabled subscription yet',
+							origin_id, target_id;
+		END IF;
+
 		SELECT INTO progress_lsn remote_commit_lsn
 			FROM spock.progress
 			WHERE node_id = target_id AND remote_node_id = origin_id;
diff --git a/src/spock.c b/src/spock.c
index 27c6ee38..6320ce6d 100644
--- a/src/spock.c
+++ b/src/spock.c
@@ -1106,11 +1106,11 @@ _PG_init(void)
 							"This setting is deprecated and has no effect. "
 							"The replay queue now dynamically allocates memory as needed.",
 							&spock_replay_queue_size,
-							4194304,
+							4,
 							0,
-							INT_MAX,
+							MAX_KILOBYTES / 1024,
 							PGC_SIGHUP,
-							0,
+							GUC_UNIT_MB,
 							NULL,
 							NULL,
 							NULL);
diff --git a/tests/tap/schedule b/tests/tap/schedule
index 6bfe6451..a1bf5672 100644
--- a/tests/tap/schedule
+++ b/tests/tap/schedule
@@ -15,6 +15,7 @@ test: 004_non_default_repset
 test: 008_rmgr
 test: 009_zodan_add_remove_nodes
 test: 010_zodan_add_remove_python
+test: 012_zodan_basics
 
 # Tests, consuming too much time to be launched on each check:
 #test: 011_zodan_sync_third
diff --git a/tests/tap/t/012_zodan_basics.pl b/tests/tap/t/012_zodan_basics.pl
new file mode 100755
index 00000000..69430255
--- /dev/null
+++ b/tests/tap/t/012_zodan_basics.pl
@@ -0,0 +1,124 @@
+use strict;
+use warnings;
+use Test::More;
+use lib '.';
+use lib 't';
+use SpockTest qw(create_cluster destroy_cluster get_test_config psql_or_bail scalar_query);
+
+my ($result);
+
+create_cluster(3, 'Create basic Spock test cluster');
+
+# Get cluster configuration
+my $config = get_test_config();
+my $node_count = $config->{node_count};
+my $node_ports = $config->{node_ports};
+my $host = $config->{host};
+my $dbname = $config->{db_name};
+my $db_user = $config->{db_user};
+my $db_password = $config->{db_password};
+my $pg_bin = $config->{pg_bin};
+
+psql_or_bail(2, "SELECT spock.node_drop('n2')");
+psql_or_bail(3, "SELECT spock.node_drop('n3')");
+psql_or_bail(1, "CREATE EXTENSION amcheck");
+psql_or_bail(2, "CREATE EXTENSION dblink");
+psql_or_bail(3, "CREATE EXTENSION dblink");
+psql_or_bail(2, "\\i ../../samples/Z0DAN/zodan.sql");
+psql_or_bail(3, "\\i ../../samples/Z0DAN/zodan.sql");
+psql_or_bail(1, "CREATE TABLE test(x serial PRIMARY KEY)");
+psql_or_bail(1, "INSERT INTO test DEFAULT VALUES");
+
+print STDERR "All supporting stuff has been installed successfully\n";
+
+# ##############################################################################
+#
+# Basic check that Z0DAN correctly add node to the single-node cluster
+#
+# ##############################################################################
+
+print STDERR "Call Z0DAN: n2 => n1\n";
+psql_or_bail(2, "
+    CALL spock.add_node(
+        src_node_name := 'n1',
+        src_dsn := 'host=$host dbname=$dbname port=$node_ports->[0] user=$db_user password=$db_password',
+        new_node_name := 'n2',
+        new_node_dsn := 'host=$host dbname=$dbname port=$node_ports->[1] user=$db_user password=$db_password',
+        verb := false
+    )");
+print STDERR "Z0DAN (n2 => n1) has finished the attach process\n";
+$result = scalar_query(2, "SELECT x FROM test");
+print STDERR "Check result: $result\n";
+ok($result eq '1', "Check state of the test table after the attachment");
+
+psql_or_bail(1, "SELECT spock.sub_disable('sub_n1_n2')");
+
+# ##############################################################################
+#
+# Z0DAN reject node addition if some subscriptions are disabled
+#
+# ##############################################################################
+
+print STDERR "Call Z0DAN: n3 => n2\n";
+scalar_query(3, "
+	CALL spock.add_node(
+		src_node_name := 'n2',
+		src_dsn := 'host=$host dbname=$dbname port=$node_ports->[1] user=$db_user password=$db_password',
+		new_node_name := 'n3', new_node_dsn := 'host=$host dbname=$dbname port=$node_ports->[2] user=$db_user password=$db_password',
+		verb := false)");
+
+$result = scalar_query(3, "SELECT count(*) FROM spock.local_node");
+ok($result eq '0', "N3 is not in the cluster yet");
+print STDERR "Z0DAN should fail because of a disabled subscription\n";
+
+psql_or_bail(1, "SELECT spock.sub_enable('sub_n1_n2')");
+psql_or_bail(3, "
+	CALL spock.add_node(
+		src_node_name := 'n2',
+		src_dsn := 'host=$host dbname=$dbname port=$node_ports->[1] user=$db_user password=$db_password',
+		new_node_name := 'n3', new_node_dsn := 'host=$host dbname=$dbname port=$node_ports->[2] user=$db_user password=$db_password',
+		verb := true)");
+
+$result = scalar_query(3, "SELECT count(*) FROM spock.local_node");
+ok($result eq '1', "N3 is in the cluster");
+$result = scalar_query(3, "SELECT x FROM test");
+print STDERR "Check result: $result\n";
+ok($result eq '1', "Check state of the test table on N3 after the attachment");
+print STDERR "Z0DAN should add N3 to the cluster\n";
+
+# ##############################################################################
+#
+# Test that Z0DAN correctly doesn't add node to the cluster if something happens
+# during the SYNC process.
+#
+# ##############################################################################
+
+# Remove node from the cluster and data leftovers.
+psql_or_bail(3, "\\i ../../samples/Z0DAN/zodremove.sql");
+psql_or_bail(3, "CALL spock.remove_node(target_node_name := 'n3',
+	target_node_dsn := 'host=$host dbname=$dbname port=$node_ports->[2] user=$db_user password=$db_password',
+	verbose_mode := true)");
+psql_or_bail(3, "DROP TABLE test");
+
+psql_or_bail(1, "CREATE FUNCTION fake_fn() RETURNS integer LANGUAGE sql AS \$\$ SELECT 1\$\$");
+psql_or_bail(3, "CREATE FUNCTION fake_fn() RETURNS integer LANGUAGE sql AS \$\$ SELECT 1\$\$");
+scalar_query(3, "
+	CALL spock.add_node(
+		src_node_name := 'n2',
+		src_dsn := 'host=$host dbname=$dbname port=$node_ports->[1] user=$db_user password=$db_password',
+		new_node_name := 'n3', new_node_dsn := 'host=$host dbname=$dbname port=$node_ports->[2] user=$db_user password=$db_password',
+		verb := true)");
+
+# TODO:
+# It seems that add_node keeps remnants after unsuccessful execution. It is
+# happened because we have commited some intermediate results before.
+# It would be better to keep remote transaction opened until the end of the
+# operation or just remove these remnants at the end pretending to be a
+# distributed transaction.
+#
+# $result = scalar_query(3, "SELECT count(*) FROM spock.local_node");
+# ok($result eq '0', "N3 is not in the cluster");
+
+# Clean up
+destroy_cluster('Destroy test cluster');
+done_testing();
diff --git a/tests/tap/t/SpockTest.pm b/tests/tap/t/SpockTest.pm
index 0333b43e..409f37c5 100644
--- a/tests/tap/t/SpockTest.pm
+++ b/tests/tap/t/SpockTest.pm
@@ -150,7 +150,7 @@ sub create_postgresql_conf {
     print $conf "spock.exception_behaviour=sub_disable\n";
     print $conf "spock.conflict_resolution=last_update_wins\n";
     print $conf "track_commit_timestamp=on\n";
-    print $conf "spock.exception_replay_queue_size=1MB\n";
+    print $conf "spock.exception_replay_queue_size='1MB'\n";
     print $conf "spock.enable_spill=on\n";
     print $conf "port=$port\n";
     print $conf "listen_addresses='*'\n";