From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Neil Conway <neilc(at)samurai(dot)com> |
Cc: | pgsql-patches <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: Hash function for numeric (WIP) |
Date: | 2007-05-08 19:19:37 |
Message-ID: | 5053.1178651977@sss.pgh.pa.us |
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Lists: | pgsql-patches |
Neil Conway <neilc(at)samurai(dot)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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