"Mark Woodward" <pgsql(at)mohawksoft(dot)com> writes:
>> Whenever someone actually writes a pg_upgrade, we'll institute a policy
>> to restrict changes it can't handle.
> IMHO, *before* any such tool *can* be written, a set of rules must be
> enacted regulating catalog changes.
That one is easy: there are no rules. We already know how to deal with
catalog restructurings --- you do the equivalent of a pg_dump -s and
reload. Any proposed pg_upgrade that can't cope with this will be
rejected out of hand, because that technology was already proven five
years ago.
The issues that are actually interesting have to do with the contents
of user tables and indexes, not catalogs.
regards, tom lane