Re: pgsql: doc: mention dependency on collation libraries

Re: Bruce Momjian 2016-07-02 <E1bJMkm-0001gS-3c@gemulon.postgresql.org>
> doc: mention dependency on collation libraries
>
> Document that index storage is dependent on the operating system's
> collation library ordering, and any change in that ordering can create
> invalid indexes.

Shouldn't this mention that OS upgrades are a possible problem as
well? We've seen the de_DE.UTF-8 ordering break in RHEL 5->6, and
again in 6->7. (5 and 7 are compatible.) The problematic strings were
"999" and "9-9-9".

(German writeup:
http://www.credativ.de/blog/postgresql-und-inkompatible-deutsche-spracheigenschaften-centosrhel)

Christoph