[mapguide-users] Sublayer in MG

[Jackie Ng]

The question is basically: X db queries for each exploded layer vs 1 db query
for a themed layer with X rules.

Theme rules require FDO filter evaluation of each feature (to resolve the
matching theme rule used to stylize it) from the root query result. The root
query result being a FDO query to the specified Feature Class and Feature
Source as specified in the Layer Definition with the Layer Definition Filter
applied if one is specified.

If we go by the rule of thumb that anything that can be passed onto the
datastore to figure out (filters/joins/etc) is faster than letting the FDO
application layer (ie. MapGuide) figuring it out then a set of exploded
layers would probably perform better than a themed one. Exploded themed
layers (if you go by Maestro's definition) have no theme rules. They only
have one. They also have a root query filter. 

Exploded theme layers have no overhead in filter evaluation (the data store
figures that out), nor do they have any overhead on theme rule resolution
(because exploded layers only have one rule).

So I'll give a cheap cop-out answer: Let a performance profiler answer that
question for you :)

- Jackie



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