The mutex_instances table lists all mutexes that the Performance Schema seeing while the server is executing.
A mutex is a code mechanism for ensuring that threads can only access resources one at a time. A second thread attempting to access a resource will find it protected by a mutex, and will wait for it to be unlocked.
The performance_schema_max_mutex_instances system variable specifies the maximum number of instrumented mutex instances.
| Column | Description |
|---|---|
NAME |
Instrument name associated with the mutex. |
OBJECT_INSTANCE_BEGIN |
Memory address of the instrumented mutex. |
LOCKED_BY_THREAD_ID |
The THREAD_ID of the locking thread if a thread has a mutex locked, otherwise NULL. |
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https://mariadb.com/kb/en/performance-schema-mutex_instances-table/