On Wed, 12 Jun 2019 at 00:06, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote: > > On 2019-May-23, Andres Freund wrote: > > > On 2019-05-23 09:37:50 -0400, Robert Haas wrote: > > > On Thu, May 23, 2019 at 9:30 AM Sergei Kornilov <s...@zsrv.org> wrote: > > > > > wal_level is PGC_POSTMASTER. > > > > > > > > But primary can be restarted without restart on standby. We require > > > > wal_level replica or highter (currently only logical) on standby. So > > > > online change from logical to replica wal_level is possible on > > > > standby's controlfile. > > > > > > That's true, but Amit's scenario involved a change in wal_level during > > > the execution of pg_create_logical_replication_slot(), which I think > > > can't happen. > > > > I don't see why not - we're talking about the wal_level in the WAL > > stream, not the setting on the standby. And that can change during the > > execution of pg_create_logical_replication_slot(), if a PARAMTER_CHANGE > > record is replayed. I don't think it's actually a problem, as I > > outlined in my response to Amit, though. > > I don't know if this is directly relevant, but in commit_ts.c we go to > great lengths to ensure that things continue to work across restarts and > changes of the GUC in the primary, by decoupling activation and > deactivation of the module from start-time initialization. Maybe that > idea is applicable for this too?
We do kind of handle change in wal_level differently at run-time versus at initialization. E.g. we drop the existing slots if the wal_level becomes less than logical. But I think we don't have to do a significant work unlike how it seems to have been done in ActivateCommitTs when commit_ts is activated. > > -- > Álvaro Herrera https://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Thanks, -Amit Khandekar EnterpriseDB Corporation The Postgres Database Company
