SQL Server 2012 SP2 Enterprise Edition. Users complaining of slowness. Monitoring tool shows highest wait event is `CXPACKET`.
* MAXDOP: 8
* Cost Threshold for Parallelism: 175
Ran `sp_BlitzCache` (from the Brent Ozar toolset, those guys rock) for further diagnosis and results show queries with cost under 175 going parallel.
Anyone ever see Cost Threshold for Parallelism being ignored?
> *Anyone ever see Cost Threshold for Parallelism being ignored?*
It is not being ignored. During the compilation process, the optimizer first considers a serial plan. If the estimated cost of that plan exceeds the Threshold, the optimizer goes on to look for a parallel plan. If the resulting parallel plan is costed below the best serial one, it will be chosen.
So, the parallel plan will have a lower cost that the serial one (which you cannot see). It is perfectly possible for the final parallel plan to have an estimated cost below the Threshold - the point is *the best serial plan candidate exceeded the Threshold*.
An example can be seen in my [blog post] on parallel plan bitmaps.