6.8.9.2 Parallelism
By default, all available processor threads are used to process PGQL
                                queries. However, if needed, the number of threads can be limited by
                                setting the parallelism option of the In-Memory
                                Analyst (PGX).
               
See Configuration Parameters for the Graph Server (PGX) Engine for more information on the graph server configuration parameters.
Parent topic: Best Practices for Tuning PGQL Queries