From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Dimitri <dimitrik(dot)fr(at)gmail(dot)com> |
Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Merlin Moncure <mmoncure(at)gmail(dot)com>, PostgreSQL Performance <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Any better plan for this query?.. |
Date: | 2009-05-19 07:25:45 |
Message-ID: | 1242717945.14551.81.camel@ebony.2ndQuadrant |
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Thread: | |
Lists: | pgsql-performance |
On Tue, 2009-05-19 at 00:33 +0200, Dimitri wrote:
> >
> > In particular, running the tests repeatedly using
> > H.REF_OBJECT = '0000000001'
> > rather than varying the value seems likely to benefit MySQL. The
>
> let me repeat again - the reference is *random*,
> the '0000000001' value I've used just to show a query execution
> plan.
>
> also, what is important - the random ID is chosen in way that no one
> user use the same to avoid deadlocks previously seen with PostgreSQL
> (see the "Deadlock mystery" note 2 years ago
> http://dimitrik.free.fr/db_STRESS_BMK_Part1.html#note_4355 )
OK, didn't pick up on that.
(Like Tom, I was thinking query cache)
Can you comment on the distribution of values for that column? If you
are picking randomly, this implies distribution is uniform and so I am
surprised we are mis-estimating the selectivity.
> I think yes (but of course I did not try to replay it several times)
If you could that would be appreciated. We don't want to go chasing
after something that is not repeatable.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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