Re: pgsql: Fix WAL replay in presence of an incomplete record

[ I'm working on the release notes ]

Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> Fix WAL replay in presence of an incomplete record
> ...
> Because a new type of WAL record is added, users should be careful to
> upgrade standbys first, primaries later. Otherwise they risk the standby
> being unable to start if the primary happens to write such a record.

Is there really any point in issuing such advice? IIUC, the standbys
would be unable to proceed anyway in case of a primary crash at the
wrong time, because an un-updated primary would send them inconsistent
WAL. If anything, it seems like it might be marginally better to
update the primary first, reducing the window for it to send WAL that
the standbys will *never* be able to handle. Then, if it crashes, at
least the WAL contains something the standbys can process once you
update them.

Or am I missing something?

regards, tom lane