"Karen Hill" <karen_hill22@xxxxxxxxx> wrote in message news:1159387540.543806.256650@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx > 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 > I generally like Kimball, but this idea sounds bogus. Of course, if you only want your data warehouse to be right some of the time....
