> [!ReplicationSlotIO] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_lwlock_replicationslotio.png"></td><td><b>Wait Category</b></td><td>LWLock</td></tr><tr><td><b>Mechanism</b></td><td><code>ReplicationSlotControlLock</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Distributed/Redistribute">Redistribute</a></td></tr><tr><td><b>Resources</b></td><td><a href="Resources/disk IO">disk IO</a>, <a href="Resources/CPU">CPU</a></td></tr><tr><td colspan="3">That a process is blocked while performing <b>Replication Slot Bookkeeping</b>. Each time a standby server acknowledges a Write-Ahead Log (WAL) record, the primary must update the slot's <code>restart_lsn</code> and <code>confirmed_flush_lsn</code> on disk to ensure the engine doesn't delete WAL segments that the standby still needs.</td></tr></table>