In the earlier days (up to OS X Lion 10.7), Server Admin had an option to “Dedicate system resources for high performance services”.
This option is no longer available in the GUI, but it still exists on the command-line.
NOTE: If you are using OS X 10.11 El Capitan or greater, you will need to disable SIP (System Integrity Protection) first.
Check if your server is running in performance mode with
If you find its NOT, its generally a good idea to enable it as performance mode tunes the system to run as a server.
You can do so by issuing:
serverinfo --setperfmode 1
When done, reboot.