The nuance to the question is in the phrase “running concurrently”. There is a limit to the number of characters one can use in a Twitter poll. My intention was for people to focus on the number of threads that could have a status of
RUNNINGat any one moment.
There are various definitions for that status in different DMVs, but essentially
RUNNINGmeans actively executing on a processor — not waiting for its turn on a CPU or for some other resource to become available.
My expectation was that most people would think that
MAXDOP 4would limit a parallel query to using 4 CPU cores at any one moment in time. Indeed, that was the second most popular answer to the poll.
But read on to understand why 4 isn’t the correct answer.