Re: Append Cost in query planners

Nimesh Satam wrote:
> We are trying to implement partition on one tables on date basis. the
> overall cost and timming and cost of the query is increasing on the Append
> of the child table output. As shown below:
>
> *-> Append (cost=0.00..112217.92 rows=2752906 width=52) (actual time=
> 2454.207..20712.021 rows=2752905 loops=1)
> -> Seq Scan on trm (cost=0.00..28570.35 rows=1 width=52) (actual time=
> 2423.374..2423.374 rows=0 loops=1)
> Filter: ((sqldate >= '2007-06-01 00:00:00'::timestamp without time zone)
> AND (sqldate <= '2007-06-03 00:00:00'::timestamp without time zone))
> -> Seq Scan on trm_d20070601 trm (cost=0.00..29203.41 rows=961094
> width=52) (actual time=30.825..3027.217 rows=961094 loops=1)
> Filter: ((sqldate >= '2007-06-01 00:00:00'::timestamp without time zone)
> AND (sqldate <= '2007-06-03 00:00:00'::timestamp without time zone))
> -> Seq Scan on trm_d20070602 trm (cost=0.00..27442.52 rows=903168
> width=52) (actual time=11.142..2687.422 rows=903168 loops=1)
> Filter: ((sqldate >= '2007-06-01 00:00:00'::timestamp without time zone)
> AND (sqldate <= '2007-06-03 00:00:00'::timestamp without time zone))
> -> Seq Scan on trm_d20070603 trm (cost=0.00..27001.64 rows=888643
> width=52) (actual time=13.697..2568.012 rows=888643 loops=1)
> Filter: ((sqldate >= '2007-06-01 00:00:00'::timestamp without time zone)
> AND (sqldate <= '2007-06-03 00:00:00'::timestamp without time zone))*
>
> Can someone let me know, how we can reduce the overall cost and time of the
> append operation, and what parameters in the confirguration needs to be
> changed?

Does the query really return almost 3 million rows? If that's the case,
I'm afraid there isn't much you can do, software-wise. If not, show us
the complete query and EXPLAIN ANALYZE output.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com