Re: Replication origins and timelines

Craig,

* Craig Ringer (craig(at)2ndquadrant(dot)com) wrote:
> On 1 June 2017 at 09:27, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> > * Craig Ringer (craig(at)2ndquadrant(dot)com) wrote:
> >> TL;DR: replication origins track LSN without timeline. This is
> >> ambiguous when physical failover is present since XXXXXXXX/XXXXXXXX
> >> can now represent more than one state due to timeline forks with
> >> promotions. Replication origins should track timelines so we can tell
> >> the difference, I propose to patch them accordingly for pg11.
> >
> > Uh, TL;DR, wow? Why isn't this something which needs to be addressed
> > before PG10 can be released? I hope I'm missing something that makes
> > the current approach work in PG10, or that there's some reason that this
> > isn't a big deal for PG10, but I'd like a bit of info as to why that's
> > the case, if it is.
>
> In Pg 10, if you promote a physical replica then logical replication
> falls apart entirely and stops working. So there's no corruption
> hazard because it just ... stops.

I see.

> This only starts becoming an issue once logical replication slots can
> exist on replicas and be maintained to follow the master's slot state.
> Which is incomplete in Pg10 (not exposed to users) but I plan to
> finish getting in for pg11, making this a possible issue to be
> addressed.

Fair enough. I'm disappointed that we ended up with that as the
solution for PG10, but so be it, the main thing is that we avoid any
corruption risk.

Thanks!

Stephen