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Spotlight on Oracle 10.9 - Getting Started Guide

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Mutex Page

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

  1. Select the Spotlight on MySQL connection in the Spotlight Browser.
  2. 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


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.


The currently executing module that has created the mutex.


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