tilly is correct. For a case where the main issue is simply small RAM, adding another library will just use more memory and exacerbate the problem.

Your situation is different. BerkeleyDB is certainly up to the task. I used the term dbfile as a generic term for databases like Berkeley and GDBM. I'm sorry if this sloppy usage was confusing.

I don't work much with large scale data processing tasks like this, but it looks like you are on the right track with your plans.

Using the berkeleyDB is a way to offload memory intensive and speed critical operations to a C library through XS. Exactly what has been widely advocated in this thread. The best thing is that someone else has already written and carefully optimized this code. What could be better than that?