Re: cyclical redundancy checksum algorithm(s)?

>> 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.
>
> "To quickly determine if rows have changed, we rely on a cyclic
> redundancy checksum (CRC) algorithm. If the CRC is identical for the
>
>> "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.

Small example of collisions for crc32:
0x38ee5531
Hundemarke
92294
0x59471e4f
raciner
tranchefiler
0x947bb6c0
Betriebsteile
4245

I had make a lot of work when choosing hash function for tsearch2. Also, I had
find that popular hash algorithms produce more collision for non-ascii
languages... CRC32 is more "smooth".
On dictionary with 332296 unique words CRC32 produces 11 collisions, perl's hash
function - 35, pgsql's hash_any - 12.

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/