> [!OldSnapshotTimeMapping] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_lwlock_procarray_individual.png"></td><td><b>Wait Category</b></td><td>LWLock</td></tr><tr><td><b>Mechanism</b></td><td><code>OldSnapshotTimeMappingLock</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>Snapshot Durability Layer</b>. The "Old Snapshot Threshold" feature (governed by <code>old_snapshot_threshold</code>) allows the database to reclaim space from dead tuples even if a long-running transaction is still active, by allowing that transaction to eventually fail with a "snapshot too old" error.</td></tr></table>