Re: Slow indexscan

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On 6/20/07, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
"Mikko Partio" <mpartio@xxxxxxxxx> writes:
> Adding a new index does not speed up the query (although the planner decides
> to use the index):

Hm.  Lots of dead rows maybe?  What's your vacuuming policy?

                        regards, tom lane



The table only gets inserts and selects, never updates or deletes so I guess vacuuming isn't necessary. Anyways:


db=# SET default_statistics_target TO 1000;
SET
db=# vacuum analyze verbose tbl_20070601;
INFO:  --Relation public.tbl_20070601--
INFO:  Index tbl_20070601_pkey: Pages 95012; Tuples 3715565: Deleted 0.
        CPU 8.63s/1.82u sec elapsed 367.57 sec.
INFO:  Index tbl_20070601_latlonvalidpar_index: Pages 27385; Tuples 3715565: Deleted 0.
        CPU 1.55s/1.22u sec elapsed 23.27 sec.
INFO:  Removed 2865 tuples in 2803 pages.
        CPU 0.30s/0.20u sec elapsed 37.91 sec.
INFO:  Pages 83950: Changed 0, Empty 0; Tup 3715565: Vac 2865, Keep 0, UnUsed 0.
        Total CPU 12.32s/3.69u sec elapsed 449.98 sec.
INFO:  Analyzing public.tbl_20070601
VACUUM
db=# set sort_mem to 50000;
SET
db=# explain analyze * from tbl_20070601 where validtime between 20070602000000 and 20070602235500 and latitude=60.2744 and longitude=26.4417 and parname in ('temperature');
                                                                                                               QUERY PLAN          
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 Index Scan using tbl_20070601_latlonvalidpar on tbl_20070601 t1  (cost=0.00..28.46 rows=13 width=137) (actual time=37.81..1415.06 rows=539 loops=1)
   Index Cond: ((latitude = 60.2744::double precision) AND (longitude = 26.4417::double precision) AND (validtime >= 20070602000000::bigint) AND (validtime <= 20070602235500::bigint) AND (parname = 'temperature'::character varying))
 Total runtime: 1416.53 msec
(3 rows)


I guess the sort_mem helped, or then part of the rows are in the cache already. Should increasing sort_mem help here since there are no sorts etc?

Regards

MP



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