From: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
---|---|
To: | Alex Drobychev <adrobj(at)yahoo(dot)com> |
Cc: | David Fetter <david(at)fetter(dot)org>, pgsql-general(at)postgresql(dot)org |
Subject: | Re: GIN: any ordering guarantees for the hits returned? |
Date: | 2007-11-20 11:20:46 |
Message-ID: | 20071120112046.GB5167@alvh.no-ip.org |
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Thread: | |
Lists: | pgsql-general |
Alex Drobychev wrote:
> I agree with this maybe 98% - but not 100%. :-) Unfortunately
> performance can change rather unpredictably when the DB stops
> fitting in memory - say, 3-4 months after a production roll-out, too
> late for profiling experiments. :-(
Surely you're capable of inventing random data to simulate the load
you'll have in 3-4 months or even a year?
David is correct in that the order is not guaranteed. It's not just a
matter of which order the rows were inserted -- the executor can do a
lot of things internally that would make the result appear in a
different order. Even when the data is CLUSTER'ed the ordering can be
lost. If you want to have a guaranteed order, use ORDER BY.
--
Alvaro Herrera Developer, http://www.PostgreSQL.org/
"Thou shalt not follow the NULL pointer, for chaos and madness await
thee at its end." (2nd Commandment for C programmers)
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