Re: Hash function for numeric (WIP) - Mailing list pgsql-patches

From Tom Lane
Subject Re: Hash function for numeric (WIP)
Date
Msg-id 5053.1178651977@sss.pgh.pa.us
Whole thread Raw
In response to Re: Hash function for numeric (WIP)  (Neil Conway <neilc@samurai.com>)
List pgsql-patches
Neil Conway <neilc@samurai.com> writes:
> On Sun, 2007-06-05 at 21:30 -0400, Tom Lane wrote:
>> It'd be a good idea if you repeat the previous number-of-collisions
>> experiment on this code.

> I repeated the same experiment, and got essentially the same number of
> collisions (829 collisions on ~2 million randomly generated numerics,
> with 273 duplicates). Since the modified hash still uses hash_any() and
> really only differs when there are leading/trailing zeros, this is
> consistent with what I'd expect.

Right, given that there presumably weren't any leading/trailing zeroes
in your sample, the digit hashing ought to be exactly the same.  I was
just worried that the slightly different treatment of the weight might
somehow invalidate the results.

            regards, tom lane

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