Syntax:
SHOW MUTEX STATUS

SHOW MUTEX STATUS displays InnoDB mutex statistics. The output fields
are:

o Mutex

  The mutex name. The name indicates the mutex purpose. For example,
  the log_sys mutex is used by the InnoDB logging subsystem and
  indicates how intensive logging activity is. The buf_pool mutex
  protects the InnoDB buffer pool.

o Module

  The source file where the mutex is implemented.

o Count indicates how many times the mutex was requested.

o Spin_waits indicates how many times the spinlock had to run.

o Spin_rounds indicates the number of spinlock rounds. (spin_rounds
  divided by spin_waits provides the average round count.)

o OS_waits indicates the number of operating system waits. This occurs
  when the spinlock did not work (the mutex was not locked during the
  spinlock and it was necessary to yield to the operating system and
  wait).

o OS_yields indicates the number of times that a thread trying to lock
  a mutex gave up its timeslice and yielded to the operating system (on
  the presumption that allowing other threads to run will free the
  mutex so that it can be locked).

o OS_waits_time os_wait_times indicates the amount of time (in ms)
  spent in operating system waits, if the timed_mutexes system variable
  is 1 (ON). If timed_mutexes is 0 (OFF), timing is disabled, so
  OS_waits_time is 0. timed_mutexes is off by default.

Information from this statement can be used to diagnose system
problems. For example, large values of spin_waits and spin_rounds may
indicate scalability problems.

SHOW MUTEX STATUS was added in MySQL 5.0.3. In MySQL 5.1, SHOW MUTEX
STATUS is renamed to SHOW ENGINE INNODB MUTEX. The latter statement
displays similar information but in a somewhat different output format.

URL: http://dev.mysql.com/doc/refman/5.0/en/show-mutex-status.html

