1 files changed, 38 insertions, 0 deletions
diff --git a/mysql-test/r/mdl_sync.result b/mysql-test/r/mdl_sync.result
index d484ab77701..de57e3859b7 100644
--- a/mysql-test/r/mdl_sync.result
+++ b/mysql-test/r/mdl_sync.result
@@ -2913,3 +2913,41 @@ UNLOCK TABLES;
 # Connection default
 UNLOCK TABLES;
 DROP DATABASE db1;
+#
+# Bug#56292 Deadlock with ALTER TABLE and MERGE tables
+#
+DROP TABLE IF EXISTS t1, t2, m1;
+CREATE TABLE t1(a INT) engine=MyISAM;
+CREATE TABLE t2(a INT) engine=MyISAM;
+CREATE TABLE m1(a INT) engine=MERGE UNION=(t1, t2);
+INSERT INTO t1 VALUES (1), (2);
+INSERT INTO t2 VALUES (3), (4);
+# Connection con1
+SET DEBUG_SYNC= 'mdl_upgrade_shared_lock_to_exclusive SIGNAL upgrade WAIT_FOR continue';
+# Sending:
+ALTER TABLE m1 engine=MERGE UNION=(t2, t1);
+# Connection con2
+# Waiting for ALTER TABLE to try lock upgrade
+SET DEBUG_SYNC= 'now WAIT_FOR upgrade';
+# Sending:
+DELETE FROM t2 WHERE a = 3;
+# Connection default
+# Check that DELETE is waiting on a metadata lock and not a table lock.
+# Now that DELETE blocks on a metadata lock, we should be able to do
+# SELECT * FROM m1 here. SELECT used to be blocked by a DELETE table
+# lock request.
+SELECT * FROM m1;
+a
+1
+2
+3
+4
+# Resuming ALTER TABLE
+SET DEBUG_SYNC= 'now SIGNAL continue';
+# Connection con1
+# Reaping: ALTER TABLE m1 engine=MERGE UNION=(t2, t1)
+# Connection con2
+# Reaping: DELETE FROM t2 WHERE a = 3
+# Connection default
+DROP TABLE m1, t1, t2;
+SET DEBUG_SYNC= 'RESET';