title: Correct hash function for primary keys
body: <p>Wondering which hashing algorithm I should be using to create primary keys from strings.  Right now I'm using SHA-1.  </p>
  
  <p>In the past I've used SHA-256, although I have heard that 256 might be 'overkill' for my purposes.  I've also heard some things about maybe using MD5, but I don't know much about the pros and cons of that one.</p>
  
  <p>Thanks!</p>