synchronized_standby_slots used in logical replication

Hi,

I'm working with logical replication in a PostgreSQL 17 setup, and I'm exploring the new synchronized_standby_slots parameter to make replication slots failover safe in a highly available environment using physical standby nodes managed by Patroni.

While testing this feature, I encountered a blocking behavior, when a standby is listed in synchronized_standby_slots and that standby goes offline, logical replication on the primary stops progressing. From what I understand, the primary node waits for the standby to acknowledge received wal records, effectively stalling WAL decoding for the logical slot. I noticed that the failover slot on the standby continue to be synced.

This raises several questions about the tradeoffs and implications of using this feature:

• What are the risks or limitations if synchronized_standby_slots is left empty (the default)? Is there a risk of data loss or inconsistency for logical subscribers in such cases?
• Is it expected behavior that any failure of a standby listed in synchronized_standby_slots stalls logical decoding on the primary? If so, are there any ways to avoid blocking WAL decoding while still having slot synchronization?
• Patroni is managing FO slots better than native Postgres impletmentation?