> [!extend] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_lock_extend.png"></td><td><b>Wait Category</b></td><td>Lock</td></tr><tr><td><b>Mechanism</b></td><td><code>RelationExtension</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Tuple/ModifyTable">ModifyTable</a>, <a href="Operations/Index/IndexScan">IndexScan</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>File Growth Serialization point</b>. To prevent multiple processes from corrupting a file by simultaneously trying to write to the same new offset, Postgres requires that only one session at a time can "grow" a specific table or index.</td></tr></table>