Re: Query planner unaware of possibly best plan - Mailing list pgsql-performance

From Alvaro Herrera
Subject Re: Query planner unaware of possibly best plan
Date
Msg-id 20070921195644.GB13986@alvh.no-ip.org
Whole thread Raw
In response to Re: Query planner unaware of possibly best plan  (Denes Daniel <panther-d@freemail.hu>)
Responses Re: Query planner unaware of possibly best plan
List pgsql-performance
Denes Daniel wrote:

> I've just inserted some newlines, so it's better to read than when my
> email-client wraps the lines automatically. Did not touch the information
> itself. But here is the normal output of EXPLAIN ANALYZE:

The best thing to do is paste them in a text file and send it as an
attachment.

>                                                               QUERY PLAN
> -------------------------------------------------------------------------------------------
> --------------------------------------------
>  Sort  (cost=100000132.10..100000140.10 rows=8 width=16) (actual
> time=0.302..0.319 rows=9 loops=1)
>    Sort Key: tparent.ord, tchild.ord
>    ->  Nested Loop  (cost=0.00..84.10 rows=8 width=16) (actual
> time=0.181..0.267 rows=9 loops=1)
>          ->  Index Scan using par_uniq_ord on tparent  (cost=0.00..20.40
> rows=4 width=8) (actual time=0.100..0.109 rows=4 loops=1)
>                Index Cond: ((ord >= 1) AND (ord <= 4))
>          ->  Index Scan using chi_pkey_parid_ord on tchild
> (cost=0.00..9.93 rows=2 width=8) (actual time=0.020..0.026 rows=2
> loops=4)
>                Index Cond: (tchild.par_id = "outer".id)
>  Total runtime: 0.412 ms
> (8 rows)
>
> The costs may be different because I've tuned the query planner's
> parameters.

Why did you set enable_sort=off?  It's not like sorting 9 rows is going
to take any noticeable amount of time anyway.

--
Alvaro Herrera                        http://www.advogato.org/person/alvherre
"No hay hombre que no aspire a la plenitud, es decir,
la suma de experiencias de que un hombre es capaz"

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