Greg Smith <gsmith@gregsmith.com> writes:
> I fully accept that it may be the case that it doesn't make technical
> sense to tackle them in any order besides sync->read-only slaves because
> of dependencies in the implementation between the two.
Well, it's certainly not been my intention to suggest that no one should
start work on read-only-slaves before we finish the other part. The
point is that I expect the log shipping issues will be done first
because they're easier, and it would be pointless to not release that
feature if we had it.
But since you mention it: one of the plausible answers for fixing the
vacuum problem for read-only slaves is to have the slaves push an xmin
back upstream to the master to prevent premature vacuuming. The current
design of pg_standby is utterly incapable of handling that requirement.
So there might be an implementation dependency there, depending on how
we want to solve that problem.
regards, tom lane