On Tue, 2019-12-31 at 15:51 -0800, Mike Lissner wrote: > Hi, I'm trying to figure out how to shorten a chain of logically > replicating servers. Right now we have three servers replicating like > so: > > A --> B --> C > > And I'd like to remove B from the chain of replication so that I only have: > > A --> C > > Of course, doing this without losing data is the goal. If the > replication to C breaks temporarily, that's fine, so long as all the > changes on A make it to C eventually. > > I'm not sure how to proceed with this. My best theory is: > > 1. In a transaction, DISABLE the replication from A to B and start a > new PUBLICATION on A that C will subscribe to in step ③ below. The > hope is that this will simultaneously stop sending changes to B while > starting a log of new changes that can later be sent to C. > > 2. Let any changes queued on B flush to C. (How to know when they're > all flushed?) > > 3. Subscribe C to the new PUBLICATION created in step ①. Create the > subscription with copy_data=False. This should send all changes to C > that hadn't been sent to B, without sending the complete tables. > > 4. DROP all replication to/from B (this is just cleanup; the incoming > changes to B were disabled in step ①, and outgoing changes from B were > flushed in step ②). > > Does this sound even close to the right approach? Logical replication > can be a bit finicky, so I'd love to have some validation of the > general approach before I go down this road. I don't think that will work. Any changes on A that take place between step 1 and step 3 wouldn't be replicated to C. You'd have to suspend all data modification on A in that interval. Yours, Laurenz Albe -- Cybertec | https://www.cybertec-postgresql.com
