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 ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
