From: | David Blewett <david(at)dawninglight(dot)net> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Bad Plan for Questionnaire-Type Query |
Date: | 2009-06-05 21:53:26 |
Message-ID: | 9d1f8d830906051453x26ccb3dfif7fd103409e1347c@mail.gmail.com |
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Lists: | pgsql-performance |
On Mon, May 25, 2009 at 11:22 AM, David Blewett <david(at)dawninglight(dot)net> wrote:
> On Sun, May 24, 2009 at 2:42 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>
>> It still feels like this schema design is obscuring correlations that
>> the planner needs to know about in order to make decent estimates.
>
> I'm not sure how to make the planner aware of these correlations. Is there
> something inherently flawed with this design? It seems pretty close to the
> one on the Varlena website [1].
>
>> You mentioned earlier that the seemingly unrelated question_ids were
>> linked via a common submission_id. I wonder whether it's possible to
>> query using the submission_id instead?
>
> Well, I do join the different response tables [text/date/etc] together via
> the submission_id. However, in order to be able to apply the where clauses
> appropriately, I have to limit the responses to the appropriate
> question_id's. Would it matter to push that requirement down to the where
> clause instead of part of the join clause?
>
> David
>
> 1. http://www.varlena.com/GeneralBits/110.php
>
Anyone have thoughts on this?
Bueller?
David
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