Message-ID: <45A681B7.8090104@pws.com.au>
Date: Fri, 12 Jan 2007 05:28:07 +1100
From: Russell Smith <mr-russ@pws.com.au>
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To: carlos.reimer@opendb.com.br
CC: pgsql-performance@postgresql.org
Subject: Re: Improving SQL performance
References: <PEEPKDFEHHEMKBBFPOOKAEDKDNAA.carlos.reimer@opendb.com.br>
In-Reply-To: <PEEPKDFEHHEMKBBFPOOKAEDKDNAA.carlos.reimer@opendb.com.br>
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Carlos H. Reimer wrote:
> Hi,
>  
> I know that the problem with the following SQL is the "LOG.CODCEP = 
> ENDE.CODCEP||CODLOG" condition, but what can I
> do to improve the performance?
>  
I wouldn't say it's the join condition.  There is a nested loop join on 
500k+ rows.
Is it possible to put an index on LOG.CODCEP?

That might give you a better plan, as you only have 1 row in the left of 
the join.  so index scan would be preferable.

Regards

Russell Smith
> Is there a type of index that could help or is there another way to 
> build this SQL?
>  
> Thank you in advance!
>  
> explain analyze
> SELECT ENDE.* , DEND.DESEND, DEND.USOEND, DEND.DUPEND,
>                to_char('F') as NOVO,
>                LOG.TIPLOG
>           FROM TT_END ENDE LEFT OUTER JOIN TD_END DEND ON DEND.CODTAB 
> = ENDE.TIPEND
>                            LEFT OUTER JOIN TT_LOG LOG ON LOG.CODCEP = 
> ENDE.CODCEP||CODLOG
>          WHERE ENDE.FILCLI = '001'
>            AND ENDE.CODCLI = ' 19475';
>  
>
>                                                             QUERY 
> PLAN                                                      
> ----------------------------------------------------------------------------------------------------------------------------------
>  Nested Loop Left Join  (cost=0.00..25366.84 rows=1259 width=417) 
> (actual time=1901.499..1901.529 rows=1 loops=1)
>    Join Filter: (("inner".codcep)::text = (("outer".codcep)::text || 
> ("outer".codlog)::text))
>    ->  Nested Loop Left Join  (cost=0.00..4.91 rows=1 width=412) 
> (actual time=0.117..0.144 rows=1 loops=1)
>          Join Filter: ("inner".codtab = "outer".tipend)
>          ->  Index Scan using pk_end on tt_end ende  (cost=0.00..3.87 
> rows=1 width=388) (actual time=0.066..0.078 rows=1 loops=1)
>                Index Cond: ((filcli = '001'::bpchar) AND (codcli = ' 
> 19475'::bpchar))
>          ->  Seq Scan on td_end dend  (cost=0.00..1.02 rows=2 
> width=33) (actual time=0.012..0.018 rows=2 loops=1)
>    ->  Seq Scan on tt_log log  (cost=0.00..12254.24 rows=582424 
> width=17) (actual time=0.013..582.521 rows=582424 loops=1)
>  Total runtime: 1901.769 ms
> (9 rows)
>  
> \d tt_log
>             Table "TOTALL.tt_log"
>  Column |          Type          | Modifiers
> --------+------------------------+-----------
>  codbai | numeric(5,0)           | not null
>  nomlog | character varying(55)  | not null
>  codcep | character(8)           | not null
>  
> \d tt_end
>                           Table "TOTALL.tt_end"
>  Column |         Type          |                Modifiers
> --------+-----------------------+-----------------------------------------
> ...
> ...
> ...
>  codlog | character(3)          |
> ...
> ...
> ...
>  codcep | character(5)          |
> ...
> ...
>
> Reimer
>
>