However, that doesn't hold for pg_upgrade. pg_upgrade will try to read
all the multixids. So we need to make the multixact reading code
tolerant of the situations that could be present after a crash. I think
the right philosophy here is that we try to read all the old multixids,
and do our best to interpret them the same way that the old server
would.
Something like attached?
Now previous scheme of upgrade with the bytes joggling start
looking not so bad. Just a funny thought that came to my mind.
Perhaps we should check that all the files exist and have the correct
sizes in the pre-check stage
Not sure about it. Because SLRU does not support "holes", simply
checking if the first and last multixacts exist will be enough. But
we'll do it anyway in a real conversion.
PFA to start a conversation.