I've evolved various techniques for constructing less memory hungry data structures that have hash-like properties. See A (memory) poor man's <strike>hash</strike> lookup table. for one example.

There are caveats with each method, in as much as, they are not general-pupose hash replacements--Perls hashes are about as good as you will get if you need the full power of them. But for any individual application, there are often more compact representations that can be utilised.

The trick is to work out what subset of the properties of a hash you require, and look for a solution that meets those requirements with a reduced memory footprint. Obviously that will come at the sacrifice of other properties that you don't need for the given application.

To be able to suggest an appropriate solution requires that you describe the use you are making of your large hash. Any solution that might result would probably not be a "module".