Keep Away From Runnable Queues

Re-Run

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There are a lot of posts about THREADPOOL on the internet, but what happens before your server threads go into the red?

You might see other signs of CPU contention — lots of waits on stuff like the CX waits, or SOS_SCHEDULER_YIELD.

But there are other signs, too, and they can show up in the lifecycle of a query.

Zombie Skeleton

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The main states a query can be in are:

• Runing: Chugging happily along
• Runnable: Waiting for a CPU
• Suspended: Waiting on something else (locks, pages, whatever)
• Sleeping: Should probably disconnect maybe, I guess

If you’ve got a lot of queries that are runnable, they’re ready to run, but not getting CPU time.

There are a ton of reasons why you might see this rack up, like:

• Too few CPUs
• Totally untuned queries
• VM issues like noisy neighbors, CPU limits, etc.
• RBAR-style code

Good News!

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Checks for this are coming to sp_BlitzFirst, and sp_PressureDetector.

If > 25% of  your queries are runnable, we’ll warn you about it. What you do with that information is up to your skilled hands.

• For sp_PressureDetector, the change will be there by the time this post drops
• For sp_BlitzFirst, watch for the February release

Thanks for reading!

Going Further

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If this is the kind of SQL Server stuff you love learning about, you’ll love my training. I’m offering a 75% discount to my blog readers if you click from here. I’m also available for consulting if you just don’t have time for that and need to solve performance problems quickly.