Some more information about the underlying problem might be good. Why do you need a set of hashes with nearly 4 billion elements? What sort of data is it, and how are you trying to manipulate the data? Perl is not exactly the most memory-efficient language in the world, and working with smaller chunks of data would be smart if at all possible. For instance, if you know that your keys are going to be random 10-char strings, you could save all record data in files named according to the first one or two characters of each key, process the files one by one, then merge the results into a master file.