> [!ReplicationSlotSync] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_io_replicationslotsync.png"></td><td><b>Wait Category</b></td><td>IO</td></tr><tr><td><b>Mechanism</b></td><td><code>ReplicationSlot</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"><b>Replication Progress Durability Barrier</b>. As a replica consumes data, the primary must periodically update the slot's "on-disk" position to ensure that if the primary crashes, it knows exactly where the replica left off.</td></tr></table>