An instrumented metadata lock operation. 

• wait/synch 

An instrumented synchronization object. For synchronization objects, the TIMER_WAIT  time includes the amount of time blocked while attempting to acquire a lock on the object, if any. 

• wait/synch/cond 

A condition is used by one thread to signal to other threads that something they were waiting for has happened. If a single thread was waiting for a condition, it can wake up and proceed with its execution. If several threads were waiting, they can all wake up and compete for the resource for which they were waiting. 

• wait/synch/mutex 

A mutual exclusion object used to permit access to a resource (such as a section of executable code) while preventing other threads from accessing the resource. 

• wait/synch/prlock 

A priority rwlock lock object. 

• wait/synch/rwlock 

A plain read/write lock object used to lock a specific variable for access while preventing its use by other threads. A shared read lock can be acquired simultaneously by multiple threads. An exclusive write lock can be acquired by only one thread at a time. 

• wait/synch/sxlock 

A shared-exclusive (SX) lock is a type of rwlock lock object that provides write access to a common resource while permitting inconsistent reads by other threads. sxlocks  optimize concurrency and improve scalability for read-write workloads. 

## 27.7 Performance Schema Status Monitoring 

There are several status variables associated with the Performance Schema: 

mysql> SHOW STATUS LIKE ’perf%’; +-----------------------------------------------+-------+ | Variable_name | Value | +-----------------------------------------------+-------+ | Performance_schema_accounts_lost | 0 | | Performance_schema_cond_classes_lost | 0 | | Performance_schema_cond_instances_lost | 0 | | Performance_schema_digest_lost | 0 | | Performance_schema_file_classes_lost | 0 | | Performance_schema_file_handles_lost | 0 | | Performance_schema_file_instances_lost | 0 | | Performance_schema_hosts_lost | 0 | | Performance_schema_locker_lost | 0 | | Performance_schema_memory_classes_lost | 0 | | Performance_schema_metadata_lock_lost | 0 | | Performance_schema_mutex_classes_lost | 0 | | Performance_schema_mutex_instances_lost | 0 | | Performance_schema_nested_statement_lost | 0 | | Performance_schema_program_lost | 0 | | Performance_schema_rwlock_classes_lost | 0 | 

