Re: cyclical redundancy checksum algorithm(s)?

"Karen Hill" <karen_hill22@yahoo.com> writes:
> 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.

You sure that's actually what he said?  A change in CRC proves the data
changed, but lack of a change does not prove it didn't.

People do sometimes use this logic in connection with much wider
"summary" functions, such as an MD5 hash.  I wouldn't trust it at all
with a 32-bit CRC, and not much with a 64-bit CRC.  Too much risk of
collision.

            regards, tom lane