Re: pgsql: Fix a couple of bugs in MultiXactId freezing

Andres Freund <andres@2ndquadrant.com> writes:
> Any idea how to cheat our way out of that one given the current way
> heap_freeze_tuple() works (running on both primary and standby)? My only
> idea was to MultiXactIdWait() if !InRecovery but that's extremly grotty.
> We can't even realistically create a new multixact with fewer members
> with the current format of xl_heap_freeze.

Maybe we should just bite the bullet and change the WAL format for
heap_freeze (inventing an all-new record type, not repurposing the old
one, and allowing WAL replay to continue to accept the old one).  The
implication for users would be that they'd have to update slave servers
before the master when installing the update; which is unpleasant, but
better than living with a known data corruption case.
        regards, tom lane