hello --

i am not a postgis user, but i am interested in range datatypes and gist 
indexing.  there are some extensions for postgresql which expose such types 
(temporal, cube, etc.) but as far as i can tell all of them use the default 
geometric operator selectivity functions, which are all stubs in mainline 
postgresql and return hard-coded constants -- not ideal.

i've been investigating postgis and it appears that you have real selectivity 
functions for your operators.

1 - is this true?  do they work well?  which operators work?  (&&, @>, etc)?

2 - is there any documentation describing how they work (besides the source 
code)?  i'm interested in the kind of statistics you use.

3 - would it be possible for someone to backport the selectivity functions to, 
say, temporal postgres or cube?  would you recommend it?

best regards, ben
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