Re: left join performance problem - Mailing list pgsql-performance

From pginfo
Subject Re: left join performance problem
Date
Msg-id 3EE8061B.1FAED8AD@t1.unisoftbg.com
Whole thread Raw
In response to left join performance problem  (pginfo <pginfo@t1.unisoftbg.com>)
Responses Re: left join performance problem
List pgsql-performance
Many thanks Tom,
the doc do not contain solution for this case, but the idea to
change the join order was excelent and all is working fine at the moment.

regards,
ivan.

Tom Lane wrote:

pginfo <pginfo@t1.unisoftbg.com> writes:
> I have a big problem with pg left join performance.

I think the problem is that the LEFT JOIN clause is forcing the
planner to join A_SKLAD to A_MESKLAD before anything else, whereas
a good plan would do some of the other joins first to eliminate
as many rows as possible.  You will need to revise the query to
let the LEFT JOIN happen later.  For discussion see
http://www.postgresql.org/docs/view.php?version=7.3&idoc=0&file=explicit-joins.html

                        regards, tom lane

 

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