Re: Delete query takes exorbitant amount of time

On Sat, 2005-03-26 at 15:18 -0800, Stephan Szabo wrote:
> On Sat, 26 Mar 2005, Karim Nassar wrote:
>
> > On Sat, 2005-03-26 at 07:55 -0800, Stephan Szabo wrote:
> > > That seems like it should be okay, hmm, what does something like:
> > >
> > > PREPARE test(int) AS SELECT 1 from measurement where
> > > id_int_sensor_meas_type = $1 FOR UPDATE;
> > > EXPLAIN ANALYZE EXECUTE TEST(1);
> > >
> > > give you as the plan?
> >
> >                                                       QUERY PLAN
> >
-----------------------------------------------------------------------------------------------------------------------
> >  Seq Scan on measurement  (cost=0.00..164559.16 rows=509478 width=6)
> >                           (actual time=11608.402..11608.402 rows=0 loops=1)
> >                           Filter: (id_int_sensor_meas_type = $1)
> >  Total runtime: 11608.441 ms
> > (3 rows)
>
> Hmm, has measurement been analyzed recently?  You might want to see if
> raising the statistics target on measurement.id_int_sensor_meas_type and
> reanalyzing changes the estimated rows down from 500k.

orfs=# ALTER TABLE measurement ALTER COLUMN id_int_sensor_meas_type SET STATISTICS 1000;
ALTER TABLE
orfs=# VACUUM FULL ANALYZE VERBOSE;
<snip>
INFO:  free space map: 52 relations, 13501 pages stored; 9760 total pages needed
DETAIL:  Allocated FSM size: 1000 relations + 300000 pages = 1864 kB shared memory.
VACUUM
orfs=# PREPARE test(int) AS SELECT 1 from measurement where
orfs-# id_int_sensor_meas_type = $1 FOR UPDATE;
PREPARE
orfs=# EXPLAIN ANALYZE EXECUTE TEST(1);
                                                     QUERY PLAN
---------------------------------------------------------------------------------------------------------------------
 Seq Scan on measurement  (cost=0.00..164559.16 rows=509478 width=6) (actual time=8948.452..8948.452 rows=0 loops=1)
   Filter: (id_int_sensor_meas_type = $1)
 Total runtime: 8948.494 ms
(3 rows)

orfs=# EXPLAIN ANALYZE EXECUTE TEST(1);
                                                     QUERY PLAN
---------------------------------------------------------------------------------------------------------------------
 Seq Scan on measurement  (cost=0.00..164559.16 rows=509478 width=6) (actual time=3956.616..3956.616 rows=0 loops=1)
   Filter: (id_int_sensor_meas_type = $1)
 Total runtime: 3956.662 ms
(3 rows)



Some improvement. Even better once it's cached. Row estimate didn't
change. Is this the best I can expect? Is there any other optimizations
I am missing?

TIA,

--
Karim Nassar
Department of Computer Science
Box 15600, College of Engineering and Natural Sciences
Northern Arizona University,  Flagstaff, Arizona 86011
Office: (928) 523-5868 -=- Mobile: (928) 699-9221