regularly added to PostgreSQL major releases, the internal data storage

format rarely changes. <application>pg_upgrade</> does its best to

make sure the old and new clusters are binary-compatible, e.g. by

checking for compatible compile-time settings. It is important that

checking for compatible compile-time settings, including 32/64-bit

binaries. It is important that

any external modules are also binary compatible, though this cannot

be checked by <application>pg_upgrade</>.

</para>