Re: Primary Key Hash help

On Tue, Aug 13, 2002 at 12:21:44AM +0900, Sean Middleditch wrote:
> Yes and yes.  MD5 is a standardized specification (thus it will always
> have the same output in all implementations, assuming no bugs are
> present), and it's size in bits is fixed (forget off the top of my head
> what size exactly it is).

128 bits.
Another fail-proof way which guarantees no clashes would be join()'ing
the fields and expanding the resulting string to a fixed size.
Anyway, collisions would be _very_ rare with MD5...
You can also make them even more uncommon this way:
        1) get the MD5sum of "#{row}"
        2) get the MD5sum of "#{row}_an arbitrary string_"
        3) concat the results from 1) and 2) and you've got a 256 bits
        "extended" MD5

You can repeat 2) as many times as you like and rest assured that
an asteroid crashing on your computer is more probable than this
"extended" MD5 giving the same value for 2 different rows :-)
You can also compare it with the probability of a hardware failure (or
that of a bug in your code, if you're really *good* at it :-)

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