![[wl_ipc_xidgen.png|256]] - **Description**: Occurs when a process is waiting to allocate a new transaction ID (XID). This acts as a serialization bottleneck because it requires acquiring the `XidGenLock` (an internal Lightweight Lock) to safely and atomically increment the monotonic transaction counter, sometimes also necessitating WAL buffer writes to record the new XID allocation boundary. - **Resources**: [[Memory]], [[CPU]]