> [!RelationMapRead] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_io_relationmapread.png"></td><td><b>Wait Category</b></td><td>IO</td></tr><tr><td><b>Mechanism</b></td><td><code>RelationMapRead</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">This wait event is a specialized I/O operation that occurs primarily during <b>Database Startup</b> or when a backend is first accessing core system catalogs. Because certain "bootstrap" catalogs (like <code>pg_class</code> and <code>pg_attribute</code>) cannot have their locations stored within themselves, Postgres uses a small "relation map" file to find them on disk.</td></tr></table>