after trying for days to overcome a memory-leak problem
Care to expand on that ? You are aware that Perl maintains its own heap, and doesn't release memory once it acquires it from the runtime heap ? Which, from external monitoring apps, may make it appear that you've got a memory leak, when in fact Perl is just doing its thing.
That said, when doing big load jobs into DBMS's, there are any number of potential concurrency pitfalls, some of which will occur in both forked and threaded environments (possibly because they occur in the DBMS itself). YMMV.
Perl Contrarian & SQL fanboy