> [!SubtransBuffer] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_lw_subtransbuffer.png"></td><td><b>Wait Category</b></td><td>LWLock</td></tr><tr><td><b>Mechanism</b></td><td><code>SubtransBufferLock</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Tuple/ModifyTable">ModifyTable</a>, <a href="Operations/Table/SeqScan">SeqScan</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 a <b>Specific Subtransaction Mapping Page</b>. The <code>pg_subtrans</code> log is a critical shared-memory structure that tracks which "Child" Transaction IDs belong to which "Parent" Transaction IDs, allowing the engine to correctly determine the visibility of tuples created within nested savepoints.</td></tr></table>