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Re: [PATCHES] updated hash functions for postgresql v1

From: Jeff Davis <pgsql(at)j-davis(dot)com>
To: Kenneth Marshall <ktm(at)rice(dot)edu>
Cc: 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 18:16:34
Message-ID: 1231611394.25019.86.camel@jdavis (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
On Sat, 2009-01-10 at 11:06 -0600, Kenneth Marshall wrote:
> > Separating mix() and final() should have some performance benefit,
> > right?
> > 
> Yes, it does but the results can be swamped by other latencies in the
> code path. Tests such as Tom's benchmark of the underlying functions is
> needed to isolate the timings effectively or a benchmark like Greenplum's
> that will benefit from a more efficient function.

Ok. I isolated the function itself by just doing:

-- 10 million rows of random()::text
EXPLAIN ANALYZE SELECT hashtext(t) FROM randomtext;

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.

I tried quickly with a few other data types and got similar results.
It's obviously a small microbenchmark, but that's good enough for me. 


	Jeff Davis

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