> [!NOTE] ![[assets/wl_lwlock_shmemindex.md|256]] > > | | | > | :--- | :--- | > | **Wait Category** | LWLock | > | **Mechanism** | `ShmemIndexLock` | > | **Operations** | [[Operations/Other/FunctionScan]] | > | **Resources** | [[Resources/RAM|Memory]], [[Resources/CPU|CPU]] | > > Contention on the **Resource Allocation Layer** of shared memory. To ensure that different parts of the engine (and loaded extensions) don't overwrite each other, Postgres uses the `ShmemIndex` to serialize the "claiming" of shared memory blocks.