Re: adding a new column in IDENTIFY_SYSTEM

Jaime Casanova <jaime(at)2ndquadrant(dot)com> writes:
> I want to propose the addition of a new field in IDENTIFY_SYSTEM:
> xlogversion, which will carry XLOG_PAGE_MAGIC from primary.
> The idea of sending that info is to allow us to know if the xlog page
> version of two different major versions are compatible or not.
> Currently pg_upgrade requires the primary to be taken down,

That's *intentional*.

The notion of WAL-shipping-replication compatibility between two
different major versions is insane on its face. They will not have
compatible system catalog contents. You might get perfect replication
of the master's catalogs, but the slave wouldn't be able to interpret
them.

The reason we have XLOG_PAGE_MAGIC is really more the opposite: to
prevent people from trying to recover across a minor version update in
which we had to break XLOG compatibility. I don't recall right now
if that's ever actually happened, but it definitely could.

regards, tom lane