Re: Horribly slow hash join

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Greg Stark <gsstark(at)mit(dot)edu>
Cc: "Jim C(dot) Nasby" <jim(at)nasby(dot)net>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Horribly slow hash join
Date: 2004-04-18 03:45:58
Message-ID: 15053.1082259958@sss.pgh.pa.us
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Greg Stark <gsstark(at)mit(dot)edu> writes:
> Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:
>> (Also, I have been harboring some notions of supporting cross-type hash
>> joins for integer types, which will not work unless small int8 values hash
>> the same as int4 etc.)

> The obvious way to modify the hash function is to xor the high 32 bits with
> the low 32 bits. That maintains the property you need

No it doesn't ...

regards, tom lane

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