select * from performance_schema.rwlock_instances limit 1;
select * from performance_schema.rwlock_instances
where name='FOO';
insert into performance_schema.rwlock_instances
set name='FOO', object_instance_begin=12;
ERROR 42000: INSERT command denied to user 'root'@'localhost' for table `performance_schema`.`rwlock_instances`
update performance_schema.rwlock_instances
set name='FOO';
ERROR 42000: UPDATE command denied to user 'root'@'localhost' for table `performance_schema`.`rwlock_instances`
delete from performance_schema.rwlock_instances
where name like "wait/%";
ERROR 42000: DELETE command denied to user 'root'@'localhost' for table `performance_schema`.`rwlock_instances`
delete from performance_schema.rwlock_instances;
ERROR 42000: DELETE command denied to user 'root'@'localhost' for table `performance_schema`.`rwlock_instances`
LOCK TABLES performance_schema.rwlock_instances READ;
ERROR 42000: SELECT, LOCK TABLES command denied to user 'root'@'localhost' for table `performance_schema`.`rwlock_instances`
UNLOCK TABLES;
LOCK TABLES performance_schema.rwlock_instances WRITE;
ERROR 42000: SELECT, LOCK TABLES command denied to user 'root'@'localhost' for table `performance_schema`.`rwlock_instances`
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='rwlock_instances';
column_name	column_comment
NAME	Instrument name associated with the read write lock
OBJECT_INSTANCE_BEGIN	Address in memory of the instrumented lock
WRITE_LOCKED_BY_THREAD_ID	THREAD_ID of the locking thread if locked in write (exclusive) mode, otherwise NULL.
READ_LOCKED_BY_COUNT	Count of current read locks held