A mutex (mutual exclusion object) is a program object (with a unique name or ID) that allows multiple threads to share the same resource. A mutex for a resource is created when a relevant program is started.
When a thread needs to use the resource, the mutex locks the resource to prevent it being used by other threads. A thread that has been locked out is put in a queue, and given control of the resource only when it reaches the front of the queue and the mutex is unlocked.
To open the mutex page
Click Activity | Mutex.
Mutex Activity Grid
A table of mutex activity for the current Spotlight on MySQL connection is displayed in the Mutex page of the Activity drilldown.
| Column | Description |
|---|---|
|
Mutex |
The name of the mutex. |
|
Mutex Count |
The total number of times a thread has obtained the mutex. |
|
Mutex Rate |
The current rate of mutex acquisitions per second. |
|
Spin Waits |
The number of times the mutex was unavailable. When this occurs, the thread spins (repeatedly attempts to acquire the mutex). |
|
Spin Wait Rate |
The current rate of spin waits. |
|
Spin Rounds |
The total number of spins attempted. |
|
OS Waits |
The total number of OS sleeps performed for the mutex. [When the mutex is NOT acquired after a certain number of spins, a thread sleeps (temporarily pauses its attempt to obtain the mutex) and tries again when it re-awakes.] |
|
OS Wait Time |
The time spent sleeping between attempts to gain the mutex. MySQL needs to be running in --timed-mutexes option for this to be populated. |
|
OS Wait Time Rate |
The current rate of OS sleeps. |
|
Module |
The currently executing module that has created the mutex. |
