cyclical redundancy checksum algorithm(s)?
Date: 27 Sep 2006 13:05:40 -0700
Message-ID: <1159387540.543806.256650_at_i3g2000cwc.googlegroups.com>
I just finished reading one of Ralph Kimball's books. In it he mentions something called a cyclical redundancy checksum (crc) function. A crc function is a hash function that generates a checksum.
I am wondering a few things. A crc function would be extremely useful
and time saving in determining if a row needs to be updated or not (are
the values the same, if yes don't update, if not update). In fact
Ralph Kimball states that this is a way to check for changes. You just
have an extra column for the crc checksum. When you go to update data,
generate a crc checksum and compare it to the one in the crc column.
If they are same, your data has not changed.
Yet what happens if there is a collision of the checksum for a row?
Ralph Kimball did not mention which algorithm to use, nor how to create a crc function that would not have collisions. He does have a PhD, and a leader in the OLAP datawarehouse world, so I assume there is a
good solution.Is there a crc function in postgresql? If not what algorithm would I need to use to create one in pl/pgsql?
regards,
karen
Received on Wed Sep 27 2006 - 22:05:40 CEST