select * from performance_schema.metadata_locks;
select * from performance_schema.metadata_locks
where object_name='foo';
OBJECT_TYPE	OBJECT_SCHEMA	OBJECT_NAME	OBJECT_INSTANCE_BEGIN	LOCK_TYPE	LOCK_DURATION	LOCK_STATUS	SOURCE	OWNER_THREAD_ID	OWNER_EVENT_ID
insert into performance_schema.metadata_locks
set object_name='FOO', owner_thread_id=1;
ERROR 42000: INSERT command denied to user 'root'@'localhost' for table `performance_schema`.`metadata_locks`
update performance_schema.metadata_locks
set owner_thread_id=12 where object_name='foo';
ERROR 42000: UPDATE command denied to user 'root'@'localhost' for table `performance_schema`.`metadata_locks`
delete from performance_schema.metadata_locks;
ERROR 42000: DELETE command denied to user 'root'@'localhost' for table `performance_schema`.`metadata_locks`
delete from performance_schema.metadata_locks
where timer_name='CYCLE';
ERROR 42000: DELETE command denied to user 'root'@'localhost' for table `performance_schema`.`metadata_locks`
LOCK TABLES performance_schema.metadata_locks READ;
ERROR 42000: SELECT, LOCK TABLES command denied to user 'root'@'localhost' for table `performance_schema`.`metadata_locks`
UNLOCK TABLES;
LOCK TABLES performance_schema.metadata_locks WRITE;
ERROR 42000: SELECT, LOCK TABLES command denied to user 'root'@'localhost' for table `performance_schema`.`metadata_locks`
UNLOCK TABLES;
#
# MDEV-25325 column_comment for performance_schema tables
#
select column_name, column_comment 
from information_schema.columns 
where table_schema='performance_schema' and table_name='metadata_locks';
column_name	column_comment
OBJECT_TYPE	Object type. One of BACKUP, COMMIT, EVENT, FUNCTION, GLOBAL, LOCKING SERVICE, PROCEDURE, SCHEMA, TABLE, TABLESPACE, TRIGGER (unused) or USER LEVEL LOCK.
OBJECT_SCHEMA	Object schema.
OBJECT_NAME	Object name.
OBJECT_INSTANCE_BEGIN	Address in memory of the instrumented object.
LOCK_TYPE	Lock type. One of BACKUP_FTWRL1, BACKUP_START, BACKUP_TRANS_DML, EXCLUSIVE, INTENTION_EXCLUSIVE, SHARED, SHARED_HIGH_PRIO, SHARED_NO_READ_WRITE, SHARED_NO_WRITE, SHARED_READ, SHARED_UPGRADABLE or SHARED_WRITE.
LOCK_DURATION	Lock duration. One of EXPLICIT (locks released by explicit action, for example a global lock acquired with FLUSH TABLES WITH READ LOCK) , STATEMENT (locks implicitly released at statement end) or TRANSACTION (locks implicitly released at transaction end).
LOCK_STATUS	Lock status. One of GRANTED, KILLED, PENDING, POST_RELEASE_NOTIFY, PRE_ACQUIRE_NOTIFY, TIMEOUT or VICTIM.
SOURCE	Source file containing the instrumented code that produced the event, as well as the line number where the instrumentation occurred. This allows one to examine the source code involved.
OWNER_THREAD_ID	Thread that requested the lock.
OWNER_EVENT_ID	Event that requested the lock.