[postgis-users] Strange result about spatial indexes?

[Jose Carlos]

Hi,
I made the table smaller for sharing. Now the table has just 1600 rows.
The effect still remains.  I tried with others tables and other PostGIS
versions, I tried even just with tables with POINT features getting similar
results.

Thanx,
Best

You can download the table from here:
http://cid-40b8dee7bf5b661f.skydrive.live.com/self.aspx/.Public/data.tgz

test3=# explain analyze select count(*) from suelos1 s1, suelos1 s2
where (s1.geom && s2.geom);
                                                                QUERY
PLAN                                  
-------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=1095.91..1095.92 rows=1 width=0) (actual
time=2840.187..2840.189 rows=1 loops=1)
   ->  Nested Loop  (cost=0.00..1079.87 rows=6416 width=0) (actual
time=0.111..2820.408 rows=13808 loops=1)
         ->  Seq Scan on suelos1 s1  (cost=0.00..130.04 rows=1604
width=4597) (actual time=0.009..2.580 rows=1604 loops=1)
         ->  Index Scan using suelos1_geom on suelos1 s2 
(cost=0.00..0.58 rows=1 width=4597) (actual time=0.778..1.729 rows=9
loops=1604)
               Index Cond: (s1.geom && s2.geom)
 Total runtime: 2840.270 ms
(6 rows)

test3=# explain analyze select count(*) from suelos1 s1, suelos1 s2
where (st_expand(s1.geom,00) && s2.geom);
                                                                QUERY
PLAN                                  
-------------------------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=1087.92..1087.93 rows=1 width=0) (actual
time=212.789..212.790 rows=1 loops=1)
   ->  Nested Loop  (cost=0.00..1087.89 rows=13 width=0) (actual
time=0.090..189.842 rows=13808 loops=1)
         ->  Seq Scan on suelos1 s1  (cost=0.00..130.04 rows=1604
width=4597) (actual time=0.012..2.632 rows=1604 loops=1)
         ->  Index Scan using suelos1_geom on suelos1 s2 
(cost=0.00..0.58 rows=1 width=4597) (actual time=0.043..0.084 rows=9
loops=1604)
               Index Cond: (st_expand(s1.geom, 0::double precision) &&
s2.geom)
 Total runtime: 212.864 ms


(6 rows)