On Thu, Nov 13, 2025 at 7:16 PM shveta malik <[email protected]> wrote: > > On Thu, Nov 13, 2025 at 6:39 PM Alexander Kukushkin <[email protected]> > wrote: > > > > > > > >> But the system can die/crash before shutdown. > > > > > > You mean it will not write WAL? > > When a logical replication slot is created we build a snapshot and also > > write to WAL: > > postgres=# select pg_current_wal_insert_lsn(); select > > pg_create_logical_replication_slot('foo', 'pgoutput'); select > > pg_current_wal_insert_lsn(); > > pg_current_wal_insert_lsn > > --------------------------- > > 0/37F96F8 > > (1 row) > > > > pg_create_logical_replication_slot > > ------------------------------------ > > (foo,0/37F9730) > > (1 row) > > > > pg_current_wal_insert_lsn > > --------------------------- > > 0/37F9730 > > (1 row) > > > > Only after that slot is marked as persistent. > > > > There can be a scenario where a replication slot is dropped and > recreated, and its WAL is also replicated to the standby. However, > before the new slot state can be synchronized via slotsync, the > primary crashes and the standby is promoted. Later, the user manually > reconfigures the old primary to follow the newly promoted standby (no > pg-rewind in play). I was wondering whether in such a case, would it > be a good idea to overwrite the newly created slot on old primary with > promoted-standby's synced slot (old one) by default? Thoughts?
I think it's an extremely rare or a mostly wrong operation that after failover (i.e., the old primary didn't shutdown gracefully) users have the old primar rejoin to the replication as the new standby without pg_rewind. I guess that pg_rewind should practically be used unless the primary server gracefully shutdowns (i.e., in switchover case). In failover cases, pg_rewind launches the server in single-user mode to run the crash recovery, advancing its LSN and cleaning all existing replication slots after rewinding the server. So I think that the reported issue doesn't happen in failover cases and we can focus on failover cases. Regards, -- Masahiko Sawada Amazon Web Services: https://aws.amazon.com
