On 23-Oct-2001 Steve Meyers wrote:
>> > At a previous job, we tested a 32-bit hash function by running it
>> > against hundreds of thousands of unique URL's stored in our
>> > database. We found one collision. A 64-bit hash is billions of
>> > times better (4 billion, to be exact).
>>
>> Good to know. I wonder how many collisions I'd find if I ran it over
>> every URL listed in the directory www.yahoo.com.
>>
>> Which 64 bit hash function did you use? Invent your own, or something
>> "off the shelf"?
>>
>
> We found a public domain one on the net see
> http://www.burtleburtle.net/bob/hash/evahash.html for some sample code.
> It's only a 32-bit hash though. However, that same page appears to have
> instructions for a 64-bit hash function as well, but I haven't tried it at
> all. I'd be curious to know how many collisions you find hashing all the
> URL's in yahoo's database :) I don't know how long that would take, but if
> you do it I'd like to hear the results.
>
> Since the hash function takes a key and an initial value, you could try
> running it with two different initial values and/or keys. This would give
> you effectively a 128-bit hash, which you could store across two fields in
> MySQL. I'm guessing that the 64-bit hash will probably be good enough
> though.
>
To store hash URL's i use :
CONV(PASSWORD('$url'),16,10)
as a bigint unsigned
2+ million (so far) & no collisions.
Regards,
--
Don Read [EMAIL PROTECTED]
-- It's always darkest before the dawn. So if you are going to
steal the neighbor's newspaper, that's the time to do it.
(53kr33t w0rdz: sql table query)
---------------------------------------------------------------------
Before posting, please check:
http://www.mysql.com/manual.php (the manual)
http://lists.mysql.com/ (the list archive)
To request this thread, e-mail <[EMAIL PROTECTED]>
To unsubscribe, e-mail <[EMAIL PROTECTED]>
Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
