Re: Can get GiST RECHECK clause to work

Hi Tom,

As far as I can tell this is the case. What I've done to test this is to
put an elog(NOTICE, ".....") in geometry_overlap() so I can tell when
it's being called and this is the result I get:

shapefile=# select * from tgr1 where the_geom &&
GeometryFromText('BOX3D(1000 10
0, 2000 2000)'::box3d, -2);
NOTICE: postgis_gist_sel called
NOTICE: search_box does not overlaps histogram, returning 0
NOTICE: returning computed value: 0.000000
NOTICE: IN GEOMETRY OVERLAP!!!!
ERROR: Operation on two GEOMETRIES with different SRIDs

shapefile=# create index tgr1_idx on tgr1 using gist (the_geom
gist_geometry_ops
);
CREATE INDEX
shapefile=# select * from tgr1 where the_geom &&
GeometryFromText('BOX3D(1000 10
0, 2000 2000)'::box3d, -2);
NOTICE: postgis_gist_sel called
NOTICE: search_box does not overlaps histogram, returning 0
NOTICE: returning computed value: 0.000000
gid | tlid | fnode | tnode | length | fedirp | fename | fetype | fedirs
| cfcc
| fraddl | toaddl | fraddr | toaddr | zipl | zipr | census1 | census2 |
cfcc1 |
cfcc2 | source | the_geom
-----+------+-------+-------+--------+--------+--------+--------+-------
-+------
+--------+--------+--------+--------+------+------+---------+---------+-
------+-
------+--------+----------
(0 rows)

shapefile=# explain analyze select * from tgr1 where the_geom &&
GeometryFromTex
t('BOX3D(1000 100, 2000 2000)'::box3d, -2);
NOTICE: postgis_gist_sel called
NOTICE: search_box does not overlaps histogram, returning 0
NOTICE: returning computed value: 0.000000

QUERY PLAN

------------------------------------------------------------------------
--------
-----------------------------------
Index Scan using tgr1_idx on tgr1 (cost=0.00..6.01 rows=1 width=327)
(actual t
ime=30.000..30.000 rows=0 loops=1)
Index Cond: (the_geom && 'SRID=-2;BOX3D(1000 100 0,2000 2000
0)'::geometry)
Total runtime: 30.000 ms
(3 rows)

shapefile=# select * from pg_amop where amopclaid=(SELECT oid FROM
pg_opclass W
ERE opcname = 'gist_geometry_ops');
amopclaid | amopsubtype | amopstrategy | amopreqcheck | amopopr
-----------+-------------+--------------+--------------+---------
17456 | 0 | 1 | t | 17410
17456 | 0 | 2 | t | 17412
17456 | 0 | 3 | t | 17413
17456 | 0 | 4 | t | 17411
17456 | 0 | 5 | t | 17409
17456 | 0 | 6 | t | 17414
17456 | 0 | 7 | t | 17415
17456 | 0 | 8 | t | 17416
(8 rows)

So before the index is created, the geometry_overlap() function is
called, but whenever an index scan is used then it's never called?

I've had a look at contrib/rtree_gist but it doesn't make much sense;
from what I can see the RECHECK clause is specified for a couple of
operators in the operator class but there is no operator defined in the
SQL file - so I'm guessing that in this case the RECHECK won't do
anything anyway? I'm wondering if I'm missing some sort of mapping
between && used for CREATE OPERATOR and the && listed in CREATE OPERATOR
CLASS?

This is happening with current CVS as of earlier today, however it looks
as if it doesn't work in 7.4 either (see
http://postgis.refractions.net/pipermail/postgis-users/2004-June/004973.
html where I was trying to get the person in question to alter the
catalogues manually to enforce the RECHECK which didn't solve the
problem for him either).

Many thanks,

Mark.

---

Mark Cave-Ayland
Webbased Ltd.
Tamar Science Park
Derriford
Plymouth
PL6 8BX
England

Tel: +44 (0)1752 764445
Fax: +44 (0)1752 764446

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> -----Original Message-----
> From: Tom Lane [mailto:tgl(at)sss(dot)pgh(dot)pa(dot)us]
> Sent: 13 June 2004 23:09
> To: Mark Cave-Ayland
> Cc: pgsql-hackers(at)postgresql(dot)org
> Subject: Re: [HACKERS] Can get GiST RECHECK clause to work
>
>
> "Mark Cave-Ayland" <m(dot)cave-ayland(at)webbased(dot)co(dot)uk> writes:
> > I'm trying to mark a GiST index as lossy using the RECHECK
> operator as
> > part of some work on PostGIS, but what happens is that the original
> > operator function is never reapplied to the results of the
> index scan.
>
> You sure? I'm pretty sure that a number of the contrib gist
> index opclasses would fail their regression tests if this were broken.
>
> As of 7.5 you cannot see the reapplication in the generated
> plan's filter condition; perhaps that got you confused?
>
> 2004-01-05 23:31 tgl
>
> * src/: backend/executor/nodeIndexscan.c,
> backend/nodes/copyfuncs.c, backend/nodes/outfuncs.c,
> backend/optimizer/path/costsize.c,
> backend/optimizer/plan/createplan.c,
> backend/optimizer/plan/setrefs.c, include/nodes/execnodes.h,
> include/nodes/plannodes.h: Instead of rechecking lossy index
> operators by putting them into the regular qpqual ('filter
> condition'), add special-purpose code to
> nodeIndexscan.c to recheck
> them. This ends being almost no net addition of code,
> because the
> removal of planner code balances out the extra executor
> code, but
> it is significantly more efficient when a lossy operator is
> involved in an OR indexscan. The old implementation
> had to recheck
> the entire indexqual in such cases.
>
>
> regards, tom lane
>