This is at least second time I see people suggesting persistent connection to SWISH++. Persistent connections are needed to make things fast where opening a new connection is slow. This might be the case for a database but not for SWISH++. I believe you can bombard SWISH++ on a local machine faster than anyone on the internate can bombard your site (argument 1: SWISH++ is fast enough) and you probably wouldn't even notice the speedup if you did persistent connection (argument 2: early optimization is the root of all evil).
In short: persistent connection would most likely be a wasted effort.
