Performance Schema rwlock_instances Table

The rwlock_instances table lists all active read-write lock instances, showing the write-lock owner and the number of waiting readers or writers.

The rwlock_instances table lists all read write lock (rwlock) instances that the Performance Schema sees while the server is executing. A read write is a mechanism for ensuring threads can either share access to common resources, or have exclusive access.

The performance_schema_max_rwlock_instances system variable specifies the maximum number of instrumented rwlock objects.

The rwlock_instances table contains the following columns:

Column	Description
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

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