Hi, On Thu, Jan 13, 2022 at 06:44:12PM -0800, Andres Freund wrote: > > The point is that we need the check for WAL writes / xid assignments / etc > *either* way. There are ways extensions could trigger problems like e.g. xid > assigned, besides bgworker doing stuff. Or postgres components doing so > unintentionally. > > Erroring out in situation where we *know* that there were concurrent changes > unacceptable during pg_upgrade is always the right call. Such errors can be > debugged and then addressed (removing the extension from s_p_l, fixing the > extension, etc). > > In contrast to that, preventing upgrades from succeeding because an extension > has a dependency on bgworkers working, just because the bgworker *could* be > doing something bad is different. The bgworker might never write, have a check > for binary upgrade mode, etc. It may not be realistic to fix and extension to > work without the bgworkers. > > Imagine something like an table access method that has IO workers or such.
IIUC if a table access method has IO workers that starts doing writes quickly (or any similar extension that *is* required to be present during upgrade but that should be partially disabled), the only way to do a pg_upgrade would be to make sure that the extension explicitly checks for the binary-upgrade mode and don't do any writes, or provide a GUC for the same, since it should still preloaded? I'm fine with that, but that should probably be documented. > > > > Andres, do you still have an objection with either preventing bgworker > > registration/launch or WAL-write during the impacted pg_upgrade steps, or a > > better alternative to fix the problem? > > I still object to the approach of preventing bgworker registration. It doesn't > provide much protection and might cause hard to address problems for some > extensions. > > I don't think I ever objected to preventing WAL-writes, I even proposed that > upthread? Unless you suggest doing it specifically in bgworkers, rather than > preventing similar problems outside bgworkers as well. Sorry I missed that when re-reading the thread. And no I'm not suggesting preventing WAL writes in bgworkers only. Since there's a clear consensus on how to fix the problem, I'm switching the patch as Waiting on Author.
