> [!RelationMapReplace] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_io_relationmapreplace.png"></td><td><b>Wait Category</b></td><td>IO</td></tr><tr><td><b>Mechanism</b></td><td><code>pg_filenode.map</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Table/SeqScan">SeqScan</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>Core Mapping Durability Barrier</b>. The Relation Map is a critical small file that provides the physical file location for system catalogs that cannot be looked up via the standard <code>pg_class</code> (because <code>pg_class</code> itself is one of those files).</td></tr></table>