A few months ago, to make a point about some of the pitfalls of fork and IO, I wrote a few tests to show the potential problems (from a Un*x perspective following the R. Stevens books for instance), and all my tests were negative in the sense that (at least on cygwin -- I think I tested HP-UX which has been my perl platform for years, but I cannot remember for sure) implicit flushing was going on ...It would be interesting to know how much perl departs from Un*x on this (and since when).

In general for this kind of problem, maybe the best way to go is a process manager maintaining a pool of processes each one with one DB connection, and some protocol to reach the process manager. Anyway I find the "forks" module interesting.