Using an MD5 Hash as an index

Question

I am writing a MongoDB Collection that contains a specific set of data, and I want to run comparisons against that data by taking an MD5 (or maybe SHA256) hash of the data and basing comparisons off of that.

I was wondering if using a fixed-length character string of hex-numbers is the right way of doing this. Is there a better datatype to use, such as a "blob" or even a 64bit long integer to hold the values? (This may require me to use a hashing function that produces longs -- I don't know of one except maybe overriding the Java .hashCode() function with Eclispe?)

If there is a better way entirely, advise on best practice would be appreciated here!

Answer 1

Storing MD5 Hashes in MongoDB

You have to use String or Binary (half the size) in case you decide to store a MD5 hash (see here ).

Best Hash Function

This is tough to answer, since it highly depends on the kind of data in your collection. I personally think that MD5 hashes are a good way, but again it depends on the use-case. In case you want to customize/optimize your hash, this post and this post might get you started. They cover some simple recipes on writing a custom hash function.