What is the optimal way to set ParralelWorkers with Classic Server?

[gsbelarus]

Consider the server has 56 cores and the Firebird serves 300 simultaneous connections in Classic mode. Does setting the MaxParallelWorkers to 16 mean that there possibly could be up to 300 * 16 = 4 800 parallel workers? Is it too many for 56 cores?

[hvlad]

Sure, 4800 active workers looks too much. But this is possible only if all 300 connections runs some parallelized task at the same time, for example restore or sweep or build index. If this is possible, even 300 active workers of this kind (with MaxParallelWorkers = 1) will be way to much for 56 cores.

[gsbelarus]

Do I understand correctly that, aside from restoring, seeping or building indexes, parallel workers don't affect the performance of any other operations?

[hvlad]

Yes. Exact list of operations that could be parallelized currently is: gbak's backup and restore, sweep, index creation.
There could be more in the next Firebird versions, of course.