pid not appropriate/unique enough as a query identifier?

[yingli017]

	switch (WaitForBackgroundWorkerStartup(worker_handle, &pid))
	{
		case BGWH_STARTED:
			/* Success. */
			break;
		case BGWH_STOPPED:
			/* Success and already done. */
			break;
		case BGWH_POSTMASTER_DIED:
			pfree(worker_handle);
			ereport(ERROR,
					(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
					 errmsg("cannot start background processes without postmaster"),
					 errhint("Kill all remaining database processes and restart the database.")));
			break;
		default:
			elog(ERROR, "unexpected bgworker handle status");
			break;
	}

	/* Store the relevant details about this worker for future use. */
	save_worker_info(pid, seg, worker_handle, responseq);

WaitForBackgroundWorkerStartup would only populate pid if BGWH_STARTED. Also depending upon how fast pid id recycled on the system, it might not be unique enough.

A proper query_id should be generated and returned to user, and later used for retrieval?