> [!RelationMapping] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_lw_relationmapping.png"></td><td><b>Wait Category</b></td><td>LWLock</td></tr><tr><td><b>Mechanism</b></td><td><code>RelationMappingLock</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Table/SeqScan">SeqScan</a>, <a href="Operations/Tuple/ModifyTable">ModifyTable</a></td></tr><tr><td><b>Resources</b></td><td><a href="Resources/RAM">Memory</a>, <a href="Resources/CPU">CPU</a></td></tr><tr><td colspan="3">Contention on the <b>Physical Identity Layer</b>. While most relations store their file identifiers in the <code>pg_class</code> catalog, core system catalogs (and objects being currently rewritten) rely on a dedicated mapping file to ensure that the engine can always find its "bootstrap" data even during recovery or after a crash.</td></tr></table>