On Wed, Feb 4, 2026 at 4:07 PM Yugo Nagata <[email protected]> wrote: > > Hi, > > I would like to propose emitting a warning when creating or enabling a > subscription while max_logical_replication_workers is set to 0. In this > case, the CREATE/ALTER SUBSCRIPTION command completes successfully without > any warning, making it difficult to notice that logical replication cannot > start. > > Of course, users can confirm whether logical replication is working by > checking system views such as pg_stat_replication or pg_stat_subscription. > However, emitting warnings explicitly in these cases would make this > situation more visible. We have seen user reports where this behavior > caused confusion, with users wondering why replication did not start. >
Hi Nagata-San. AFAIK the default for `max_logical_replication_workers` is 4. So how does the maximum get to be 0 unless the user had explicitly configured it that way? Also subscriptions require multiple workers in order to work properly [1] so why check only 0? Why not check 1 or 2 or 3.... those low numbers are also likely to cause similar problems aren't they? And what about when the `max_logical_replication_workers` is 100, but those 100 are already being used. IOW, would it be more useful to warn when you do not have enough *available* workers for the Subscription to function properly, rather than checking what the maximum value is set to? ====== [1] https://www.postgresql.org/docs/current/runtime-config-replication.html#GUC-MAX-LOGICAL-REPLICATION-WORKERS Kind Regards, Peter Smith Fujitsu Australia
