When you say that the process "almost stops", do you mean that it slows down? At that point what does ps say about its size, cpu time, page faults, etc.?

My guess is that you are running into some limitation of DBM. Instead of using DBM I would suggest that you use a relational database. I think the schema would be very simple, and then you could more easily slice n' dice your data depending on what kind of reports you needed. With DBM you are choosing a preferred storage format which may not work so well for collecting other kinds of statistics. Also, putting your data into a relational database could allow you to hand-off the analyzing of the data to someone else. The data becomes more useful in the sense that more people can use it.