Potential Problems With Persistent Connections & Regenerating Sessions

Are there any potential problems or obstacles to be aware of when using MySQL persistent connections or regenerating sessions through the PHP function session_regenerate_id() ?

I read somewhere that using session_regenerate_id() could be a problem because it leaves the old session data "open" and it holds up other scripts that are trying to access that page. I don't want my pages to load one by one, meaning that one user has to wait for another user's page to fully load before his loads. However I'm unsure about that and I need someone to verify this claim.

Also, what are the pros and cons of using persistent connections with MySQL?

As far as I know, it's a persistent connection when you connect to the database but do not use mysql_close to close the connection. I also heard that this could come in conflict with the max connections because if more than 200 users (or whatever the max connection option is set to), then MySQL will reject all other connections. Anyway, I don't know much about that either.

So… problems of persistent connections and regenerating sessions?