Manage huge database

Why don't you make one pass through your data and encode you
characters as integers (it would appear that you only have 16
combinations).  You might also want to consider using the 'raw' object
since these only take up one byte of storage -- will reduce your
storage requirements by 4.  Then store each row in a 'filehash' object
so you can quickly retrieve a row at a time and then index directly to
the byte(s) that have the information that you want.