modify custom variables

Hi,

When creating postgis extension, a call to DefineCustomStringVariable is made to define postgis.backend.

An assign hook allows to change the library used by spatial functions whith a:

    SET postgis.backend = 'sfcgal'; -- or 'geos'

Everything work fine execept when upgrading postgis.

If I understand the problem correctly, on upgrate (ALTER EXTENSION), the old postgis library is already loaded, the old spatial functions are replaced by new ones pointing to the new postgis library, a call to DefineCustomStringVariable is made and:

    ERROR:  attempt to redefine parameter "postgis.backend"

I need to redefine the assign hook such that is calls the new library backend and not the old one.

Is there a way to remove/modify custom variables ? I looked in guc.h but couldn't find anything.

Thanks,

V.



PS: I'm working on http://trac.osgeo.org/postgis/ticket/2382.