An idle persistent process doesn't use any CPU either (unless it has set up some background work) so there really shouldn't be much difference. I think at the

An idle persistent process doesn't use any CPU either (unless it has set up some background work) so there really shouldn't be much difference. I think at the extremes process-per-request and persistent processes look very similar. A fresh process will read data from the disk cache, but it may need to parse or transform that data before it is usable. A persistent process will have (some) pre-parsed data in memory. If you have swap enabled it will also be swapped out to disk if the process is idle. This may be faster if parsing that data into an in-memory structure is slow or slower if this results in more IO than the source data (which may be stored more efficently).