Hi, On Mon, Jan 06, 2025 at 10:32:52PM -0800, Masahiko Sawada wrote: > On Mon, Jan 6, 2025 at 3:20 AM Ashutosh Bapat > <ashutosh.bapat....@gmail.com> wrote: > > > > On Sat, Jan 4, 2025 at 6:03 AM Masahiko Sawada <sawada.m...@gmail.com> > > wrote: > > > > > > On Fri, Jan 3, 2025 at 6:31 AM Euler Taveira <eu...@eulerto.com> wrote: > > > > > > > > On Fri, Jan 3, 2025, at 10:14 AM, Bertrand Drouvot wrote: > > > > > > > > If we don't want to force wal_level = logical to enable logical > > > > decoding (your > > > > second idea) then I think that it would be better to "hide" everything > > > > behind > > > > logical replication slot creation / deletion. That would mean that > > > > having at > > > > least one logical replication slot created would be synonym to > > > > "activate logical > > > > decoding" and zero logical replication slot created would be synonym to > > > > "deactivate > > > > logical decoding". > > > > > > > > > > > > I like this idea. The logical replication slot existence already has the > > > > required protections and guarantees (no running transactions from the > > > > past while > > > > creating) for logical decoding. > > > > > > I agree that it's better behavior. > > > > > > > > > > > Having said that, you are basically folding 'logical' machinery into > > > > 'replica'. > > > > The 'logical' option can still exists but it will be less attractive > > > > because it > > > > increases the WAL volume even if you are not using logical replication. > > > > I don't > > > > know if the current 'logical' behavior (WAL records for logical > > > > decoding even > > > > if there is no active logical replication) has any use case (maybe > > > > someone > > > > inspects these extra records for analysis) but one suggestion (separate > > > > patch) > > > > is to make 'logical' synonymous with the new 'replica' behavior (logical > > > > decoding capability). This opens the door to remove 'logical' in future > > > > releases (accepted as synonym but not documented). > > FYI one possible use case of the 'logical' level would be that if we > support retrieving WAL records for logical decoding from somewhere > like restore_command in the future, users would like to keep the > wal_level 'logical' or keep the logical decoding active.
Another use case is to allow logical decoding from standby. One could set wal_level to logical on the primary to be able to create a logical replication slot on the standby (without having the need to create one on the primary). BTW, currently it's mandatory to set wal_level to logical on the primary to be able to create a logical replication slot on the standby. Should we extend this to "logical decoding is enabled on the primary" too? Regards, -- Bertrand Drouvot PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
