> [!MessageQueueSend] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_ipc_messagequeuesend.png"></td><td><b>Wait Category</b></td><td>IPC</td></tr><tr><td><b>Mechanism</b></td><td><code>shm_mq_send</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Table/SeqScan">SeqScan</a>, <a href="Operations/ResultSet/HashJoin">HashJoin</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>Producer-Consumer Bottleneck</b> within a parallel query. In a parallel-aware plan, workers "produce" results and send them to the leader backend (the "consumer") via a small, fixed-size buffer in shared memory.</td></tr></table>