[postgis-devel] automatic BVOL on spatial columns

[Paul Ramsey]

Sounds good and simple to me, good stuff!

P

strk at refractions.net wrote:

> I've made canonical, (E)WKT and (E)WKB and GEOS input methods
> call a function returning wheter it's worth to cache bbox, and
> add it accordingly. None of this methods will face the problem
> of wheter to drop an existing cache, as transport formats do
> not contain that information. GEOS Geometry could potentially
> store an Envelope, but that's not automatically converted by
> the existing converters.
> 
> Note that many geometry editors decide wheter or not to
> add a bbox cache to their return based on other heuristics.
> Some of them add a bbox if its input geom does have a cache
> already ( transform, translate, reverse, simplify, segmentize ),
> some always avoid a bbox computation ( collect, addpoint ).
> 
> To make this behaviour consistent every function returning
> a geometry should call the heuristic functions and explicitly
> cache a bbox when the conditions match. 
> 
> Still I'm convinced that the user should have more control
> over this aspect, more specifically she should decide when
> exactly to compute it in a chain of calls, to improve performace.
> Users willing to have this finer control can set AUTOCACHE_BBOX
> to 0 in Makefile.config. In this case internal functions should
> compute a bbox only if that is a simple operation (ie: does not
> require a scan of the geometry points). The implemented trigger
> would be then useful to ensure that tables used for frequent
> selects always have a bbox cached.
>