> I don't see a "substantial additional burden" there. What I would
> imagine is needed is that the slave transmits a single number back
> --- its current oldest xmin --- and the walsender process publishes
> that number as its transaction xmin in its PGPROC entry on the master.
If the main purpose of the slave is long-running queries, though, this
could cause a lot of bloat on the master. That's a special case, but a
reason why we would want to preserve the stop replication functionality.
> I don't doubt that this approach will have its own gotchas that we
> find as we get into it. But it looks soluble. I have no faith in
> either the correctness or the usability of the approach currently
> being pursued.
So, why not start working on it now, instead of arguing about it? It'll
be easy to prove the approach once we have some test code.