GROUP BY errors: group duplication or MCS-2056: There was an IO error during a disk-based aggregation: No such file or directory

Sometimes ExeMgr returns an error during disk aggregation. The occurrence of this error strongly depends on the environment: the number of threads, the size of the data, and so on.

Another issue caused by the same root cause is occasional groups duplicates returned by GROUP BY. There is no way to reproduce it every time but there is a scenario that triggers the issue with some probability.