Please reply: Why are indices not supported in sdo_geom.relate?

Question

Hi,
I read somewhere in the newsgroup that the spatial indicesa re
used in the sdo_relate operator but not in the sdo_geom.relate
function. Could someone please let me know why this difference?
Thanks,
Hemant.R

Answer 1

Hi,
The SDO_GEOM.RELATE function should be used when comparing a
small number of geometries geometries with an area-of-interest.
The SDO_RELATE operator should be used when comparing an
area-of-interest with a layer, and it will use the index on the
layer.
There are reasons why the SDO_GEOM.RELATE function exists. If
you have two geometries that were created as part of an
application, however they aren't stored in a table and neither
one is indexed, sdo_geom.relate is a convenient way of testing or
determining what the relationship is between the geometries.
Regarding the SDO_LEVEL you are using for indexing - 17 seems
pretty high, and it might take a long time to create an index at
level 17 using geometries the size of states - you might want to
try increasing the SDO_LEVEL from 8 to 10 and see if that makes a
difference before going higher.
One thing you can do is look at the geometries using Spatial
Index Advisor - you can also see the fixed size tiles and do some
queries to get a sense of the amount of work being done by the
index as well as the work being done in the relate portion of the
operator.
Hope this helps,
Dan