Once we did that and I restarted all of the services, I ended up getting an interesting error message from SQL Server:
Msg 7320, Level 16, State 110, Line 2
Cannot execute the query “Remote Query” against OLE DB provider “SQLNCLI11” for linked server “(null)”. EXTERNAL TABLE access failed due to internal error: ‘Java exception raised on call to JobSubmitter_SubmitJob: Error [org.apache.hadoop.yarn.exceptions.InvalidResourceRequestException: Invalid resource request, requested memory < 0, or requested memory > max configured, requestedMemory=1536, maxMemory=512
The error message is pretty clear: the Polybase service wants to create containers that are 1536 MB in size, but the maximum size I’m allowing is 512 MB. Therefore, the Polybase MapReduce operation fails.
Long story short, I needed enough RAM to be able to give 4 1/2 GB to YARN for creating MapReduce containers in order to run my query.