[HACKERS] Can get GiST RECHECK clause to work
Hi everyone, 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. The operator class and operator definitions looks like this: CREATE OPERATOR ( LEFTARG = GEOMETRY, RIGHTARG = GEOMETRY, PROCEDURE = geometry_overlap, COMMUTATOR = '', RESTRICT = postgis_gist_sel, JOIN = positionjoinsel ); and: CREATE OPERATOR CLASS gist_geometry_ops DEFAULT FOR TYPE geometry USING gist AS OPERATOR1 RECHECK, OPERATOR2 RECHECK, OPERATOR3 RECHECK, OPERATOR4 RECHECK, OPERATOR5 RECHECK, OPERATOR6 ~= RECHECK, OPERATOR7 ~ RECHECK, OPERATOR8 @ RECHECK, FUNCTION1 ggeometry_consistent (internal, geometry, int4), FUNCTION2 gbox_union (bytea, internal), FUNCTION3 ggeometry_compress (internal), FUNCTION4 rtree_decompress (internal), FUNCTION5 gbox_penalty (internal, internal, internal), FUNCTION6 gbox_picksplit (internal, internal), FUNCTION7 gbox_same (box, box, internal); What I'm expecting is that since RECHECK is specified, PostgreSQL will identify the index entries using the operator and then call geometry_overlap() function with the full tuples from the heap. However, it seems geometry_overlap() is never called from an index scan made using the operator :( Can anyone point out where I'm going wrong? 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 This email and any attachments are confidential to the intended recipient and may also be privileged. If you are not the intended recipient please delete it from your system and notify the sender. You should not copy it or use it for any purpose nor disclose or distribute its contents to any other person. ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [HACKERS] Can get GiST RECHECK clause to work
Mark Cave-Ayland [EMAIL PROTECTED] 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
---(end of broadcast)---
TIP 9: the planner will ignore your desire to choose an index scan if your
joining column's datatypes do not match
Re: [HACKERS] 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: 0.00
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: 0.00
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: 0.00
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
This email and any attachments are confidential to the intended
recipient and may also be privileged. If you are not the intended
recipient please delete it from your system and notify the sender. You
should not copy it or use it for any purpose nor disclose or distribute
its contents to any other person.
-Original Message-
From: Tom Lane [mailto:[EMAIL PROTECTED]
Sent: 13 June 2004 23:09
To: Mark Cave-Ayland
Cc: [EMAIL PROTECTED]
Subject: Re: [HACKERS] Can get GiST RECHECK clause to work
Mark Cave-Ayland [EMAIL PROTECTED] 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
Re: [HACKERS] Can get GiST RECHECK clause to work
Mark Cave-Ayland [EMAIL PROTECTED] writes: 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() Well, I can easily prove that CVS tip does call the operator function and honor its result. regression=# create table foo (f1 float8 unique); NOTICE: CREATE TABLE / UNIQUE will create implicit index foo_f1_key for table foo CREATE TABLE regression=# insert into foo values(1); INSERT 480998 1 regression=# insert into foo values(2); INSERT 480999 1 regression=# select * from foo where f1 = 1; f1 1 (1 row) With gdb, I set a breakpoint at float8eq, and determine that it is called exactly once (during _bt_checkkeys' scan setup) in this query. Next, after some fooling about to determine which row in pg_amop describes float8eq: regression=# update pg_amop set amopreqcheck = true regression-# where amopclaid = 1972 and amopsubtype = 0 and amopstrategy = 3; UPDATE 1 Now the select calls float8eq twice, once from _bt_checkkeys and once from IndexNext. Moreover I can force a zero result from float8eq in the second call, and if I do then no rows are returned. My guess is that your problem occurs because the index is not returning the row in the first place, and thus there is nothing to recheck. This would point to a bug somewhere in your GIST support functions. regards, tom lane ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
