Re: select count is too slow

You don't have accurate stats over that table.

Try this after deleting:
VACUUM ANALYZE test2;

I suggest to activate autovacuum in your postgresql.conf, so you won't
have to analyze table by hand.

-----Original Message-----
From: Kumar Anand <kumar(dot)anand(at)merceworld(dot)com>
To: pgsql-admin(at)postgresql(dot)org
Subject: [ADMIN] select count is too slow
Date: Thu, 20 Aug 2009 15:06:45 +0530

Dear all,

I face this problem from last few days.

here is test2 table with only one column id
erp_test=> \d test2
Table "public.test2"
Column | Type | Modifiers
--------+---------+-----------
id | integer |

I insert 10,000,000 entries in this table.
erp_test=> INSERT INTO test2 VALUES (generate_series(1,10000000));
INSERT 0 10000000

then i delete all the entries
erp_test=> delete from test2;
DELETE 10000000

and i insert only 10 entries
erp_test=> INSERT INTO test2 VALUES (generate_series(1,10));
INSERT 0 10

now i try to count no of rows in this table which take long time for
this 10 rows only
(about 2-3 second)
erp_test=> SELECT count(*) from test2;
count
-------
10
(1 row)

this is the output of explain analyze query of the same

erp_test=> EXPLAIN ANALYZE SELECT count(*) from test2;
QUERY
PLAN
------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=198652.13..198652.14 rows=1 width=0) (actual
time=2123.471..2123.472 rows=1 loops=1)
-> Seq Scan on test2 (cost=0.00..169732.70 rows=11567770 width=0)
(actual time=2123.454..2123.454 rows=10 loops=1)
Total runtime: 2123.609 ms
(3 rows)

can any one solve my problem to speed up my select count query.

--
Thanks & Regards
Kumar Anand