> [!LockFileAddToDataDirRead] > <table><tr><td rowspan="4" width="25%"><img src="assets/wl_io_lockfileaddtodatadirread.png"></td><td><b>Wait Category</b></td><td>IO</td></tr><tr><td><b>Mechanism</b></td><td><code>postmaster.pid</code></td></tr><tr><td><b>Operations</b></td><td><a href="Operations/Table/SeqScan">SeqScan</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>Runtime Identity Verification stall</b>. The <code>postmaster.pid</code> file is the ultimate authority on whether a Postgres instance is already running in a given directory, storing the process ID and port information.</td></tr></table>