> [!WALRead] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_io_walread.png"></td><td><b>Wait Category</b></td><td>IO</td></tr><tr><td><b>Mechanism</b></td><td><code>WALRead</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Distributed/Redistribute">Redistribute</a>, <a href="Operations/Other/SubqueryScan">SubqueryScan</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">This wait event is primarily observed during <b>Crash Recovery</b>, <b>Physical Standby replay</b>, or <b>Logical Decoding</b>. While the database normally only writes WAL during ordinary operation, it must read WAL to reconstruct state after a crash or to synchronize a replica.</td></tr></table>