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InnoDB 1.1 for MySQL 5.5 User's Guide
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8.7. More Compact Output of SHOW ENGINE INNODB MUTEX

The statement SHOW ENGINE INNODB MUTEX displays information about InnoDB mutexes and rw-locks. Although this information is useful for tuning on multi-core systems, the amount of output can be overwhelming on systems with a big buffer pool. There is one mutex and one rw-lock in each 16K buffer pool block, and there are 65,536 blocks per gigabyte. It is unlikely that a single block mutex or rw-lock from the buffer pool could become a performance bottleneck.

SHOW ENGINE INNODB MUTEX now 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 outside of the buffer pool that have caused at least one OS-level wait.

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