Soft-NUMA Doesn’t Limit MAXDOP

Lonny Niederstadt tests whether soft-NUMA forces MAXDOP = 1:

I mentioned that I was planning to set up a soft-NUMA node for each vcpu on a 16 vcpu VM, to evenly distribute incoming connections and thus DOP 1 queries over vcpus.  Thomas Kejser et al used this strategy to good effect in “The Data Loading Performance Guide”, which used SQL Server 2008 as a base.

My conversation partner cautioned me that leaving this soft-NUMA configuration in place after the specialized workload would result in DOP 1 queries whether I wanted them or not.  The claim was, effectively, a parallel query plan generated by a connection within a soft-NUMA node would have its MAXDOP restricted by the scheduler count (if lower than other MAXDOP contributing factors).  Though I wasn’t able to test at the time, I was skeptical: I’d always thought that soft-NUMA was consequential to connection placement, but not to MAXDOP nor to where parallel query workers would be assigned.

I’m back home now… time to test!!

Read on for the test.

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