sporadic failures of main.mdl_sync

main.mdl_sync 'innodb'                   w32 [ fail ]
        Test ended at 2024-04-06 14:11:15

CURRENT_TEST: main.mdl_sync
--- main/mdl_sync.result
+++ main/mdl_sync.reject
@@ -2458,6 +2458,7 @@
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_FTWRL2	Backup lock
+MDL_SHARED	Table metadata lock	test	t2
 unlock tables;
 connection default;
 # Reaping UPDATE

mysql-test/main/mdl_sync.result

@@ -2433,6 +2433,9 @@ create table t1 (a int) engine=myisam;
 create table t2 (a int) stats_persistent=0, engine=innodb;
 insert into t1 values (1);
 insert into t2 values (1);
+connect  con1, localhost, root;
+start transaction with consistent snapshot;
+connection default;
 SET DEBUG_SYNC= 'after_open_table_mdl_shared SIGNAL table_opened WAIT_FOR grlwait execute 2';
 update t1,t2 set t1.a=2,t2.a=3;
 connection con2;
@@ -2464,6 +2467,7 @@ connection default;
 SET DEBUG_SYNC= 'RESET';
 drop table t1,t2;
 disconnect con2;
+disconnect con1;
 #
 # Bug#50786 Assertion `thd->mdl_context.trans_sentinel() == __null' 
 #           failed in open_ltable()

mysql-test/main/mdl_sync.test

@@ -3117,6 +3117,12 @@ create table t2 (a int) stats_persistent=0, engine=innodb;
 insert into t1 values (1);
 insert into t2 values (1);
 
+connect (con1, localhost, root);
+# disable innodb purge thread, otherwise it might start purging t2,
+# and will take an mdl, affecting metadata_lock_info output.
+start transaction with consistent snapshot;
+connection default;
+
 SET DEBUG_SYNC= 'after_open_table_mdl_shared SIGNAL table_opened WAIT_FOR grlwait execute 2';
 --send update t1,t2 set t1.a=2,t2.a=3
 
@@ -3162,6 +3168,7 @@ connection default;
 SET DEBUG_SYNC= 'RESET';
 drop table t1,t2;
 disconnect con2;
+disconnect con1;
 
 --echo #
 --echo # Bug#50786 Assertion `thd->mdl_context.trans_sentinel() == __null'