Lightweight Databases

General code is slower than special code

For example:

        sub uppercase_username {
          my ($file, $username) = @_;
          for (@$file) {
            last if s/^$username:/\U$username:/;
          }
        }

This builds and maintains an offset table in case you visit any of the early records again
If you don't, the time spent is wasted
The first version of uppercase_username didn't have to do that