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Re: Major differences between oracle and postgres performance - what can I do ?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Stephen Frost <sfrost(at)snowman(dot)net>
Cc: Gary Cowell <gary_cowell(at)yahoo(dot)co(dot)uk>,pgsql-performance(at)postgresql(dot)org
Subject: Re: Major differences between oracle and postgres performance - what can I do ?
Date: 2004-06-18 17:01:51
Message-ID: 22514.1087578111@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-performance
Stephen Frost <sfrost(at)snowman(dot)net> writes:
> * Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)us) wrote:
>> [... thinks for awhile ...]  It seems possible that they may use sort
>> code that knows it is performing a DISTINCT operation and discards
>> duplicates on sight.  Given that there are only 534 distinct values,
>> the sort would easily stay in memory if that were happening.

> Could this optimization be added to PostgreSQL?  It sounds like a very
> reasonable thing to do.

That's what I was wondering about too.  But first I'd like to get
some kind of reading on how effective it would be.  If someone can
demonstrate that Oracle can do sort-and-drop-dups a lot faster than
it can do a straight sort of the same amount of input data, that
would be a strong indication that it's worth doing.  At this point
we don't know if that's the source of their win or not.

			regards, tom lane

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