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Unkillable Threads

Paul Randal gives us a supervillain origin story:

While I was teaching IEPTO2 last week, I was discussing why sometimes a thread cannot be terminated using the KILL command, and thought it would make a great topic for a post.

Some of you have likely seen a phenomenon called a non-yielding scheduler. This is where a thread is using the processor and doesn’t voluntarily yield after using more than the thread quantum (4 milliseconds, unchangeable). There’s a background task called the scheduler monitor that checks that progress is being made on the various schedulers inside SQL Server and issues a warning if it finds a problem.

Read on to learn more about how this can happen and what it means for you.