Re: pgsql: doc: mention dependency on collation libraries

Re: Bruce Momjian 2016-07-02 <20160702155517(dot)GD18610(at)momjian(dot)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