Adding clarification on extension_control_path when extension is present in multiple folders

When playing with the new GUC extension_control_path, I found that the 
paths are evaluated one by one
(like search_path)and if an extension is present in multiple paths, only 
the on in the first path
will be considered.I think this is totally fine, but I'd like to adda 
documentation patch to explain
this (attached file).

What do you think ?

Pierrick,


Here is an example to understand that I can only create extension in 
version 2.0.

postgres=# show extension_control_path ;
extension_control_path
-----------------------------------------------------------------------------
  $system:/extensions/meilleureextension/share:/extensions/monextension/share
(1 row)

postgres=# select * from pg_available_extensions where name like '%mon%';
      name     | default_version | installed_version |    comment
--------------+-----------------+-------------------+---------------
  monextension | 2.0             |                   | Meilleure
  monextension | 1.0             |                   | Mon extension
(2 rows)
postgres=# select * from pg_available_extensions where name like '%mon%';
      name     | default_version | installed_version |    comment
--------------+-----------------+-------------------+---------------
  monextension | 2.0             |                   | Meilleure
  monextension | 1.0             |                   | Mon extension
(2 rows)
postgres=# create extension monextension version "1.0" ;
ERROR:  extension "monextension" has no installation script nor update 
path for version "1.0"
postgres=# create extension monextension ;
CREATE EXTENSION
postgres=# select * from pg_available_extensions where name like '%mon%';
      name     | default_version | installed_version |    comment
--------------+-----------------+-------------------+---------------
  monextension | 2.0             | 2.0               | Meilleure
  monextension | 1.0             | 2.0               | Mon extension
(2 rows)