The statement SHOW ENGINE INNODB MUTEX displays information about InnoDB mutexes and rw-locks. It can be a useful tuning aid on multi-core systems. However, with a big buffer pool, the size of the output may be overwhelming. There is a mutex and rw-lock in each 16K buffer pool block. It is highly improbable that an individual block mutex or rw-lock could become a performance bottleneck, and there are 65,536 blocks per gigabyte.

Starting with InnoDB 1.0.4, SHOW ENGINE INNODB MUTEX skips the mutexes and rw-locks of buffer pool blocks. It also does not list any mutexes or rw-locks that have never been waited on (os_waits=0). Thus, SHOW ENGINE INNODB MUTEX only displays information about mutexes and rw-locks that do not belong to the buffer pool blocks, and that have caused at least one OS level wait.