In reply to Glenn Horton.

Thank you, Glenn, for your comment and suggested resources. Obviously, you can optimize performance by fine-tuning and proper configuration to get the best out of it, but still with two processes running in parallel on a multi-processor single machine there will be some resources (memory, I/O, etc.) these two processes will be competing for, while there will be no such competition when they run one by one. Therefore, total duration will be cut slightly less than in half.