locale setting. For details see <xref linkend="multibyte">.
</para>
+ <para>
+ 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 reason,
+ a cluster cannot switch to an incompatible collation library version,
+ either through snapshot restore, binary streaming replication, or
+ <application>pg_upgrade</> run.
+ </para>
+
<sect2 id="creating-cluster-mount-points">
<title>Use of Secondary File Systems</title>