That's good advice. I would go one step further to advocate DB_File (or more recently BerkleyDB) as it is the ultimate persistent hash'es especially big ones, and I quote
Berkeley DB's high performance and scalability support thousands of simultaneous users working on databases as large as 256 terabytes.

 

______crazyinsomniac_____________________________ Of all the things I've lost, I miss my mind the most. perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"