XE_TIMER_MUTEX is recorded when a thread waits for access to the data structure holding the Extended Events engine’s timers, such as those implementing each session’s MAX_DISPATCH_LATENCY. Timer registration and firing serialise briefly on this mutex.
It completes the XE timer trio with XE_TIMER_EVENT (the timers ticking) and the dispatcher waits (buffers being delivered).
Is It a Problem?
No; it has not been a contention point, and its amounts stay trivial even with many event sessions. The timers themselves are lightweight, and their bookkeeping more so.
There is no XE performance question that routes through this mutex; session overhead is about event volume and predicates, and delivery health is about buffers and targets.
Common Causes
- Event sessions starting, stopping, and running their dispatch timers, system_health included.
What To Do
- Filter it out of wait analysis with the rest of the
XE_*background set. - Nothing else; there is no tuning surface.
How To See It
Rank waits with Get-WaitStatistics, where it is filtered as XE machinery noise.
Part of the SQL Server Wait Types Library.
Related deep dive: ASYNC_NETWORK_IO Wait Type.
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