> You'd have to suspend all data modification on A in that interval. I know how to stop the DB completely, but I can't think of any obvious ways to make sure that it doesn't get any data modification for a period of time. Is there a trick here? This is feeling a bit hopeless. Thanks for the response, Laurenz. On Tue, Jan 7, 2020 at 3:11 AM Laurenz Albe <laurenz.albe@xxxxxxxxxxx> wrote: > > 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 >
