Hi:
Attached to the e-mail is the body of the query and
the result of the EXPLAIN (Sorry for not placing the
query and EXPLAIN in the e-mail body . The query is
rather complicated and the EXPLAIN result is rather
long ).
The file demo.out.3 is the result of the EXPLAIN
The file demo.sql is the sql statement.
I would like your opinion on how to tune the query
as posted in the attachment
Note that I have indexes on the all the column
customer_id on both sc_customer_attr and
sc_add_points.
I am wondering why sequential scan was used the on
the clause a.customer_id = b.customer_id since the
previous join condition has an "exist" subquery with
LIMIT with filters out unneccesary customer_id before
performing the join (a_customer_id = b.customer_id).
Also I was wondering why the number of rows in the
last sequential scan is still 7 million plus (most of
the should already have been elimated by the
subquery).
Note that before the executing the query, the
database has been VACUUMed and ANALYZEd. The result of
EXPLAIN ANALYZE is almost similar to one produce by
issuing the EXPLAIN.
Any hints on tuning the query?
thank you
ludwig
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psql:demo.sql5:31: NOTICE: QUERY PLAN:
Limit (cost=602630531.21..602630531.21 rows=10 width=69)
-> Sort (cost=602630531.21..602630531.21 rows=218145 width=69)
-> Aggregate (cost=602583597.46..602609774.87 rows=218145 width=69)
-> Group (cost=602583597.46..602596686.16 rows=2181451 width=69)
-> Sort (cost=602583597.46..602583597.46 rows=2181451 width=69)
-> Merge Join (cost=602162862.44..602184219.45
rows=2181451 width=69)
-> Sort (cost=600998172.01..600998172.01 rows=52125
width=49)
-> Merge Join (cost=600994410.42..600994904.87
rows=52125 width=49)
-> Sort (cost=13.25..13.25 rows=302
width=25)
-> Seq Scan on sc_attr c
(cost=0.00..3.30 rows=302 width=25)
-> Sort (cost=600994397.17..600994397.17
rows=64485 width=24)
-> Seq Scan on sc_customer_attr a
(cost=0.00..600990276.11 rows=64485 width=24)
SubPlan
-> Limit
(cost=736.25..736.25 rows=1 width=20)
-> Subquery Scan z
(cost=736.25..736.25 rows=1 width=20)
-> Limit
(cost=736.25..736.25 rows=1 width=20)
-> Sort
(cost=736.25..736.25 rows=1 width=20)
->
Aggregate (cost=0.00..736.24 rows=1 width=20)
-> Group (cost=0.00..736.24 rows=1 width=20)
-> Index Scan using xie2sc_add_points on sc_add_points d (cost=0.00..736.24
rows=1 width=20)
-> Sort (cost=1164690.44..1164690.44 rows=7354200
width=20)
-> Seq Scan on sc_add_points b
(cost=0.00..138679.20 rows=7354200 width=20)
explain select count(distinct(b.customer_id)) as members,
sum(b.total_loyalty) as sales,
count(b.customer_id) as visits,
c.attr_cd,
c.attr_type_cd,
c.description as description
from sc_customer_attr a,
sc_add_points b,
sc_attr c
where exists (select z.customer_id
from (select d.customer_id,
sum(d.total_loyalty) as points
from sc_add_points d
where d.transdate >= 19980100.000000 and
d.transdate <= 20020931.000000 and
d.company_cd = 1 and d.branch_cd = 13 and
a.customer_id = d.customer_id
group by d.customer_id
order by points desc
limit 100 ) as z
) and
a.attr_cd = c.attr_cd and
a.attr_type_cd = c.attr_type_cd and
a.attr_type_cd = 2 and
a.company_cd = c.company_cd and
b.customer_id = a.customer_id
group by c.attr_type_cd,
c.attr_cd,
c.description
order by c.description asc
LIMIT 10 OFFSET 0;
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