Primarily sessions will live in RAM. And I was going to use MongoDB to persist sessions just in case the daemon dies or session is not found in RAM as a fallbac

Primarily sessions will live in RAM. And I was going to use MongoDB to persist sessions just in case the daemon dies or session is not found in RAM as a fallback. The reason for using MongoDB is because it's my primary database. But your concern about growing table of sessions is valid, which I will handle by periodically archiving the old sessions so that index sizes remain small.