Also called: slot sync setting
In plain English
sync_replication_slots is the PostgreSQL 17 standby setting that, when turned on, launches the slot sync worker to keep failover-enabled slots synchronized from the primary. It needs three things in place: a physical slot back to the primary (primary_slot_name), hot_standby_feedback = on, and the database name in primary_conninfo.
Why it matters
It’s the on-switch for failover-safe logical replication on the standby side. Without those prerequisites the worker can’t keep the synced slots at a safe position, so getting all three right is the foundation of the feature.