Lightweight Databases

Gappy Files

        sub modify {

        ... continued ...

          } else { # New record is too big
            my $fill = "\0" x length($oldrec);
            print $fh $fill;
            seek $fh, 0, SEEK_END;  # New record goes at the end
            print $fh $rec, "\n";
          }
        }

Here the new record won't fit
- We remove the old record entirely, and put the new one at the end
Say we're changing gnat:A51FSA8JrmV6M\n to torkington:A51FSA8JrmV6M\n
- We replace gnat:A51FSA8JrmV6M\n with \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\n
- We put torkington:A51FSA8JrmV6M\n at the end of the file
find will ignore the \0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\n 'gap'
A sufficiently clever implementation might put something else into the gap later