Hi, On 2020-06-09 08:52:24 +0200, Peter Eisentraut wrote: > On 2020-06-08 23:32, Andres Freund wrote: > > On 2020-06-08 13:27:50 -0400, Tom Lane wrote: > > > If we can allow wal_level to be changed on the fly, I agree that would > > > help reduce the pressure to make the default setting more expensive. > > > I don't recall why it's PGC_POSTMASTER right now, but I suppose there > > > was a reason for that ... > > > > There's reasons, but IIRC they're all solvable with reasonable effort. I > > think most of it boils down to only being able to rely on the new > > wal_level after a while. For minimal->recovery we basically need a > > checkpoint started after the change in configuration, and for > > recovery->logical we need to wait until all sessions have a) read the > > new config setting b) finished the transaction that used the old > > setting. > > The best behavior from a user's perspective would be if the WAL level > automatically switched to logical if logical replication slots are present. > You might not even need 'logical' as an actual value of wal_level anymore, > you just need to keep a flag in shared memory that records whether at least > one logical slot exists.
Yea, it'd be good to have that. But you'd need the same type of coordination mentioned above, no? Greetings, Andres Freund
