[postgis-devel] Prepared Geometry API

[David Fuhry]

Paul Ramsey wrote:
>> E.g. the left side of intersects will most always come from the same set of
>> data
>> and the right side of intersects will come from some other dataset.
>>
>> When we pull it out of the PG_DATAUM array or whatever isn't that pulling it
>> out based on some generated pointer already.  Why can't we just compare
>> these PG pointers and if they are the same its the same geometry.
> 
> That would indeed be ideal. More information is needed, however :)

Theoretical counterexample: If postgres palloc()s for a geometry, then 
pfree()s it, then palloc()s for the next geometry, and if the address 
returned points to the same memory location as the previous palloc(), 
then a pointer-caching technique would give a false positive.

Only if you could guarantee a unique memory location for each geometry 
seen in the (sub)query would that work.