Slot synchronization
Also called: slot sync, replication slot sync
Slot synchronization is the PostgreSQL 17 mechanism that copies failover-enabled replication slots from the primary onto a standby. A background slot sync worker (or the pg_sync_replication_slots() function) reads the primary's slots and maintains local synced copies, advanced only to positions the standby has safely received.
What this means
The Postgres 17 mechanism that copies failover-marked replication slots from the primary onto a standby. A background worker reads the primary's slots and keeps local copies, advancing them only to positions the standby has definitely received, so the copy never points past what the standby actually holds.
Why it matters operationally
It is what makes a failover slot actually survive: the bookmark is kept current on the standby in real time, so after promotion the new primary already has it. The synced copies are read-only placeholders until the standby is promoted.