I think these days there's no reason for the split between the archive and hot_standby wal levels. The split was made out of volume and stability concerns. I think we can by now be confident about the wal_level = hot_standby changes (note I'm not proposing hot_standby = on).
So let's remove the split. It just gives users choice between two options that don't have a meaningful difference.
+1.
Additionally I think we should change the default for wal_level to hot_standby and max_wal_senders (maybe to 5). That way users can use pg_basebackup and setup streaming standbys without having to restart the primary. I think that'd be a important step in making setup easier.
Yes, please!
Those who want to optimize their WAL size can set it back to minimal, but let's make the default the one that makes life *easy* for people.
The other option, which would be more complicated (I have a semi-finished patch that I never got time to clean up) would be for pg_basebackup to be able to dynamically raise the value of wal_level during it's run. It would not help with the streaming standby part, but it would help with pg_basebackup. That could be useful independent - for those who prefer using wal_level=minimal and also pg_basebackup..
Previously there have been arguments against changing the default of wal_level because it'd mean the regression tests wouldn't exercise minimal anymore. That might be true, but then right now we just don't exercise the more complex levels. If we're really concerned we can just force a different value during the tests, just as we do for prepared xacts.
Seems we should focus our tests on the stuff that people actually use in reality? :) And if we change the default, then even more people will use that level.
But it would definitely be a good idea to have some buildfarm animals set up to test each one.
Comments?
Additionally, more complex and further into the future, I wonder if we couldn't also get rid of wal_level = logical by automatically switching to it whenever logical slots are active.
If it can be safely done online, I definitely think that would be a good goal to have. If we could do the same for hot_standby if you had physical slots, that might also be a good idea?
