Re: pgsql: doc: mention dependency on collation libraries

Re: Bruce Momjian 2016-07-02 <20160702155517.GD18610@momjian.us>
> > 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".
>
> Yes, we can do that.  Do you have suggested wording?  I was not sure how
> to tell people anything related to collation versions.

How about simply this: ?

   Non<literal>C</> and and non-<literal>POSIX</> locales rely on the
   operating system's collation library for character set ordering.
   This controls the ordering of keys stored in indexes.  For this
eason,
   a cluster cannot switch to an incompatible collation library
ersion,
   either through

+  operating system upgrade,

   snapshot restore, binary streaming replication, or
   <application>pg_upgrade</> run.

Christoph