Syntax:
SHOW MUTEX STATUS

SHOW MUTEX STATUS displays InnoDB mutex statistics. From MySQL 5.0.3 to
5.0.32, the statement displays the following output fields:

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 permitting other threads to run will free the
  mutex so that it can be locked).

o OS_waits_time 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.

From MySQL 5.0.33 on, the statement uses the same output format as that
just described, but only if UNIV_DEBUG was defined at MySQL compilation
time (for example, in include/univ.i in the InnoDB part of the MySQL
source tree). If UNIV_DEBUG was not defined, the statement displays the
following fields. In the latter case (without UNIV_DEBUG), the
information on which the statement output is based is insufficient to
distinguish regular mutexes and mutexes that protect rw-locks (which
permit multiple readers or a single writer). Consequently, the output
may appear to contain multiple rows for the same mutex.

o File

  The source file where the mutex is implemented.

o Line

  The line number in the source file where the mutex is created. This
  may change depending on your version of MySQL.

o OS_waits

  Same as OS_waits_time.

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 deprecated and SHOW ENGINE INNODB MUTEX should be used
instead. The latter statement displays similar information but in a
somewhat different output format. SHOW MUTEX STATUS is removed in MySQL
5.5.

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

