> [!spectoken] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_lock_spectoken.png"></td><td><b>Wait Category</b></td><td>Lock</td></tr><tr><td><b>Mechanism</b></td><td><code>SpeculativeInsertion</code></td></tr><tr><td><b>Operations</b></td><td><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"><b>Optimistic Concurrency Barrier</b>. To handle the <code>ON CONFLICT</code> clause efficiently, Postgres allows a session to "speculatively" insert a row into a table before it is 100% certain that the unique constraint won't be violated by a concurrent transaction.</td></tr></table>