The following bug has been logged online:

Bug reference: 2196
Logged by:
Email address: agattik (AT) gmail (DOT) com
PostgreSQL version: 8.1.2
Operating system: alphaev68-dec-osf5.1a
Description: Useless RECHECK on RTREE index
Details:

create table tpoints (x int, y int);
CREATE INDEX i_tpoints ON tpoints USING RTREE (box(point(x,y),
point(x,y)));
explain select * from tpoints where box '((0,0),(1,1))' && box(point(x,y),
point(x,y));


QUERY PLAN

----------------------------------------------------------------------------
----------------------------------------------------------------------------
---
Bitmap Heap Scan on tpoints (cost=1.05..10.46 rows=10 width=8)
Recheck Cond: ('(1,1),(0,0)'::box && box(point((x)::double precision,
(y)::double precision), point((x)::double precision, (y)::double
precision)))
-> Bitmap Index Scan on i_tpoints (cost=0.00..1.05 rows=10 width=0)
Index Cond: ('(1,1),(0,0)'::box && box(point((x)::double precision,
(y)::double precision), point((x)::double precision, (y)::double
precision)))
(4 rows)

The RECHECK is necessary in case of polygons, but useless in case of box
overlap.

pg_amop.amopreqcheck is correctly set to false, but the planner seems to
ignore that.

select pg_amop.* from pg_amop join pg_opclass c ON (amopclaid=c.oid) join
pg_operator op ON (amopopr=op.oid) where opcname='box_ops' and
oprname='&&';
amopclaid | amopsubtype | amopstrategy | amopreqcheck | amopopr
-----------+-------------+--------------+--------------+---------
425 | 0 | 3 | f | 500
2593 | 0 | 3 | f | 500
(2 rows)

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match

"" <agattik (AT) gmail (DOT) com> writes:
You don't understand what a bitmap scan's recheck condition is for.
The above plan is correct.

regards, tom lane

---------------------------(end of broadcast)---------------------------
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