On Wed, Sep 30, 2015 at 5:07 PM, Ron Lindhoudt <[email protected]> wrote:
> Not sure if this helps:
> - If you really need the OR you can maybe rewrite the query and use a
> UNION
> - As far as I know Oracle cannot use an index if OR is used. Are there any
> databases that do this?
>
Peter's issue should be solved by his fix.
As for the more general case of dateline crossing, yes, in theory we could
use a UNION. But that would
mean, we have to maintain a separate codebase for Oracle, which we tried in
the past, and resulted
in the Oracle store being abandoned while the others were marching on.
Currently we have a shared set of classes for all spatial databases, and a
dialect for each one, to
sort out the differences in syntax and the like, it makes it much easier to
keep most databases
on par, but deviations like this one are hard to manage.
About databases using indexes in case of OR over selective clauses, yes,
it's somewhat
simple for a good designed optimizer, you do two index scans and pick the
union of the
tuple ids, it's well worth it if the index is deemed to be selective.
I've been told Oracle can do it, but only in the enterprise version.
Postgresql will do it in
the one and only free version instead ;-)
Here is an example with two bboxes, and the explain showing the two index
scans being merged
> explain select count(*) from osm_roads where geometry &&
ST_MakeEnvelope(12000000,4000000,12100000,4100000,3857) or geometry &&
ST_MakeEnvelope(13000000,4000000,13100000,4100000,3857);
Aggregate (cost=18629.08..18629.09 rows=1 width=0)
-> Bitmap Heap Scan on osm_roads (cost=278.66..18612.20 rows=6755
width=0)
Recheck Cond: ((geometry &&
'0103000020110F000001000000050000000000000060E366410000000080844E410000000060E3664100000000D0474F41000000003414674100000000D0474F4100000000341467410000000080844E410000000060E366410000000080844E41'::geometry)
OR (geometry &&
'0103000020110F0000010000000500000000000000A8CB68410000000080844E4100000000A8CB684100000000D0474F41000000007CFC684100000000D0474F41000000007CFC68410000000080844E4100000000A8CB68410000000080844E41'::geometry))
-> BitmapOr (cost=278.66..278.66 rows=6762 width=0)
-> Bitmap Index Scan on osm_roads_geom (cost=0.00..211.44
rows=5220 width=0)
Index Cond: (geometry &&
'0103000020110F000001000000050000000000000060E366410000000080844E410000000060E3664100000000D0474F41000000003414674100000000D0474F4100000000341467410000000080844E410000000060E366410000000080844E41'::geometry)
-> Bitmap Index Scan on osm_roads_geom (cost=0.00..63.85
rows=1542 width=0)
Index Cond: (geometry &&
'0103000020110F0000010000000500000000000000A8CB68410000000080844E4100000000A8CB684100000000D0474F41000000007CFC684100000000D0474F41000000007CFC68410000000080844E4100000000A8CB68410000000080844E41'::geometry)
(8 rows)
and here is the case of the same bbox, showing the planner is smart enough
to even avoid doing the merge, it recognizes the bbox is the same and does
a single scan:
> explain select count(*) from osm_roads where geometry &&
ST_MakeEnvelope(12000000,4000000,12100000,4100000,3857) or geometry &&
ST_MakeEnvelope(12000000,4000000,12100000,4100000,3857);
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Aggregate (cost=15214.68..15214.69 rows=1 width=0)
-> Bitmap Heap Scan on osm_roads (cost=212.74..15201.63 rows=5220
width=0)
Recheck Cond: (geometry &&
'0103000020110F000001000000050000000000000060E366410000000080844E410000000060E3664100000000D0474F41000000003414674100000000D0474F4100000000341467410000000080844E410000000060E366410000000080844E41'::geometry)
-> Bitmap Index Scan on osm_roads_geom (cost=0.00..211.44
rows=5220 width=0)
Index Cond: (geometry &&
'0103000020110F000001000000050000000000000060E366410000000080844E410000000060E3664100000000D0474F41000000003414674100000000D0474F4100000000341467410000000080844E410000000060E366410000000080844E41'::geometry)
I believe Oracle cannot do this last type of evaluation because we are
using prepared statements, and it's not able to re-evaluate the plan that
was setup when parsing the version of the stataments with the ?
(placeholders) inside
Cheers
Andrea
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