Question

I have fired a command SHOW ENGINE INNODB STATUS; in mysql for detecting slowness in response, following is the stacktrace of Semaphore, but as I am new to this, so can’t figure out statistics, please let me know if we can trace something from it.

SEMAPHORES
----------
OS WAIT ARRAY INFO: reservation count 22124, signal count 103334
Mutex spin waits 2140674, rounds 1742014, OS waits 8304
RW-shared spins 24931, OS waits 4171; RW-excl spins 1775, OS waits 8282
Spin rounds per wait: 0.81 mutex, 10.20 RW-shared, 210.67 RW-excl

Answer 1

Have a look the MySQL documentation for InnoDB Monitors. It says:

This [SEMAPHORES] section reports threads waiting for a semaphore and statistics on
how many times threads have needed a spin or a wait on a mutex or a
rw-lock semaphore. A large number of threads waiting for semaphores
may be a result of disk I/O, or contention problems inside InnoDB.
Contention can be due to heavy parallelism of queries or problems in
operating system thread scheduling.