Last fall I got some help for the list on how to use Postgres as a
source for a tile index that gives locations of raster files on disk and
that has been working beautifully.
My new question is this: Is it possible for a tile index location to
indicate something other than a path to a file, such as a PostGIS table?
The reason that I ask is that I have implemented table partitioning for
large county-by-county (or smaller) data sets such as SSURGO and USDA
CLU. At the outset I convinced myself mistakenly that Postgres could
leverage spatial check constraints for query planning using the
constraint_exclusion = on mechanism, but it can't. It only works with
fields where the check constraint is based on a straight equal/not-equal
comparison to a constant, AFAICT. Neither && ::geometry or ~ ::text
checks work for this reason.
Getting Mapserver to leverage this advanced query planning means adding
logic to my application to inject appropriate values into a WHERE clause
in the layer's DATA query string. To do this I need some kind of
generalized layer that indicates the spatial organization of the
attributes used for the partitioning. This is essentially a tile index,
so if I could just create a layer of bounding boxes for each table and
let Mapserver decide which tables it needs to scan rather than adding
complexity to my application in order to have the query planner do the
same thing, that would be ideal.
Anybody have any thoughts or experiences to share? Thanks.
Neil
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