Query Optimization

Hi,
Can anyone suggest why this query so slow.

SELECT version();
version
---------------------------------------------------------------------------------------------------------

PostgreSQL 8.4.2 on i386-portbld-freebsd7.2, compiled by GCC cc (GCC)
4.2.1 20070719 [FreeBSD], 32-bit
(1 row)
explain analyze SELECT DT.value,
DT.meassure_date,
DT.ms_status_id as status_id,
S.descr_bg as status_bg,
S.descr_en as status_en,
VT.id as value_type_id,
VT.descr_en as value_type_en,
VT.descr_bg as value_type_bg,
T.unit as value_type_unit,
T.name as general_value_type,
T.ms_db_type_id
FROM
ms_data AS DT,
ms_statuses AS S,
ms_value_types AS VT,
ms_types AS T,
ms_commands_history AS CH
WHERE DT.ms_value_type_id = 88 AND
DT.meassure_date >= '2010-04-01 1:00:00' AND
DT.meassure_date <= '2010-04-01 1:10:00' AND
DT.ms_command_history_id = CH.id AND
CH.ms_device_id = 7 AND
DT.ms_value_type_id = VT.id AND
VT.ms_type_id = T.id AND
DT.ms_status_id = S.id
GROUP BY value,
meassure_date,
status_id,
status_bg,
status_en,
value_type_id,
value_type_en,
value_type_bg,
value_type_unit,
general_value_type,
ms_db_type_id
ORDER BY meassure_date DESC;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Group (cost=23.93..23.96 rows=1 width=229) (actual
time=63274.021..63274.021 rows=0
loops=1)
-> Sort (cost=23.93..23.94 rows=1 width=229) (actual
time=63274.016..63274.016 rows=0 loops=1)
Sort Key: dt.meassure_date, dt.value, dt.ms_status_id, s.descr_bg,
s.descr_en, vt.id, vt.descr_en, vt.descr_bg, t.unit, t.name,
t.ms_db_type_id
Sort Method: quicksort Memory: 17kB
-> Nested Loop (cost=0.00..23.92 rows=1 width=229) (actual
time=63273.982..63273.982 rows=0
loops=1)
-> Nested Loop (cost=0.00..19.64 rows=1 width=165) (actual
time=63273.977..63273.977 rows=0
loops=1)
-> Nested Loop (cost=0.00..15.36 rows=1 width=101)
(actual time=63273.974..63273.974 rows=0
loops=1)
-> Nested Loop (cost=0.00..11.08 rows=1 width=23)
(actual time=63273.970..63273.970 rows=0
loops=1)
-> Index Scan using
ms_commands_history_ms_device_id_idx on ms_commands_history ch
(cost=0.00..4.33 rows=1 width=8) (actual time=0.163..25254.004 rows=9807
loops=1)
Index Cond: (ms_device_id = 7)
-> Index Scan using
ms_data_ms_command_history_id_idx on ms_data dt (cost=0.00..6.74 rows=1
width=31) (actual time=3.868..3.868 rows=0 loops=9807)
Index Cond:
(dt.ms_command_history_id = ch.id)
Filter: ((dt.meassure_date >=
'2010-04-01 01:00:00'::timestamp without time zone) AND
(dt.meassure_date <= '2010-04-01 01:10:00'::timestamp without time zone)
AND (dt.ms_value_type_id = 88))
-> Index Scan using ms_value_types_pkey on
ms_value_types vt (cost=0.00..4.27 rows=1 width=82) (never
executed) Index Cond:
(vt.id = 88)
-> Index Scan using ms_types_pkey on ms_types t
(cost=0.00..4.27 rows=1 width=72) (never
executed)
Index Cond: (t.id = vt.ms_type_id)
-> Index Scan using ms_statuses_pkey on ms_statuses s
(cost=0.00..4.27 rows=1 width=68) (never
executed) Index
Cond: (s.id = dt.ms_status_id)
Total runtime: 63274.256 ms

Thanks in advance.

Kaloyan Iliev