On Fri, May 30, 2025 at 4:32 PM Amit Kapila <amit.kapil...@gmail.com> wrote: > > On Fri, May 30, 2025 at 4:05 PM Amul Sul <sula...@gmail.com> wrote: > > > > Quick question -- due to my limited understanding of this area: why > > can't we perform an action similar to pg_logical_slot_get_changes() > > implicitly from pg_sync_replication_slots()? Would there be any > > implications of doing so? > > > > Yes, there would be implications if we did it that way. It would mean > that the consumer of the slot may not process those changes (for which > sync_slot API has done the get_changes) and send it to the client. > Consider a publisher-subscriber and physical standby setup. In this > setup, the subscriber creates a logical slot corresponding to the > subscription on the publisher. Now, the publisher process changes and > sends it to the subscriber; then the slot is advanced (both its xmin > and WAL locations) once the corresponding changes are sent to the > client. > > If we allow pg_sync_replication_slots() to do > pg_logical_slot_get_changes or equivalent in some way, then we may end > up advancing the slot without sending the changes to the subscriber, > which would be considered a data loss for the subscriber. > > I have explained in terms of built-in logical replication, but the > external plugins using these APIs (pg_logical_*) should be doing > something similar to process the changes and advance the slot. > > Does this answer your question and make sense to you? >
Yes, understood. Thank you! Regards, Amul
