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Re: [PATCHES] updated hash functions for postgresql v1

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Jeff Davis <pgsql(at)j-davis(dot)com>
Cc: Kenneth Marshall <ktm(at)rice(dot)edu>, pgsql-hackers(at)postgresql(dot)org, pgsql-patches(at)postgresql(dot)org
Subject: Re: [PATCHES] updated hash functions for postgresql v1
Date: 2009-01-10 18:36:25
Message-ID: 23860.1231612585@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> I ran 5 times on both old and new code, eliminating the top and bottom
> and taking the average of the remaining 3, and I got a 6.9% performance
> improvement with the new code.

The question that has been carefully evaded throughout the discussion
of this patch is whether the randomness of the hash result is decreased,
and if so what is that likely to cost us in performance of the various
hash-dependent algorithms.  I would still like to have an answer to that
before we make a change to gain marginal performance improvement in
the hash function itself (which is already shown to be barely measurable
in the total context of a hash-dependent operation...)

			regards, tom lane

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