During operation, PMDF frequently handles messages by scheduling processes through OpenVMS batch queues. PMDF uses OpenVMS queues because they offer enormous advantages, including flexibility in scheduling, cluster-wide submission of processes, and cluster-wide load balancing through the use of generic and execution queues. Batch jobs, however, do present overhead that can be significant in heavy message load environments. That overhead generally comes from scheduler processing within the VMS print/batch subsystem and from process creation as PMDF batch jobs execute. Batch jobs also write log files, even when such log files are not necessary.

Overhead due to OpenVMS queue handling has been significantly reduced as of OpenVMS V5.5. Overhead due to process creation can be significantly reduced by using the PMDF Process Symbiont instead of standard batch queues for scheduling the execution of PMDF processes.

The PMDF Process Symbiont has been implemented as a multi-threaded server symbiont. A single Process Symbiont is capable of handling up to 32 execution queues. A job submitted to a Process Symbiont queue will be executed by a detached process created by the symbiont as needed. Unlike a standard batch job, however, the server process will not be deleted when the job completes. The server process will wait for the symbiont to present it with another command. If the symbiont does not reuse a server process within a timeout period, the server process will exit in order to free up a process slot. Process creation overhead is reduced the most during periods of heavy PMDF load as multiple messages can be handled by the server process without the timeout period expiring. Since Process Symbiont queues are also careful to generate channel job log files only when (a) an error occurs that needs to be logged, or (b) debugging is enabled for the channel, use of Process Symbiont queues also reduces the number of log files written.