When queries are optimized, the configuration parameters affect query plans.
max parallel degree limits:
The number of worker processes for a partition-based scan
The total combined number of worker processes for nested-loop join queries, where parallel access methods are used on more than one table
The number of worker processes used for the merge and sort steps in merge joins
The number of worker processes that can be used by parallel sort operations
max scan parallel degree limits the number of worker processes for hash-based table scans and index scans.
