Function ExplainOpenWorker

src/backend/commands/explain.c:5239–5296

* Begin or resume output into the set-aside group for worker N. */

 * Begin or resume output into the set-aside group for worker N.
 */
static void
ExplainOpenWorker(int n, ExplainState *es)
{
	ExplainWorkersState *wstate = es->workers_state;

	Assert(wstate);
	Assert(n >= 0 && n < wstate->num_workers);

	/* Save prior output buffer pointer */
	wstate->prev_str = es->str;

	if (!wstate->worker_inited[n])
	{
		/* First time through, so create the buffer for this worker */
		initStringInfo(&wstate->worker_str[n]);
		es->str = &wstate->worker_str[n];

		/*
		 * Push suitable initial formatting state for this worker's field
		 * group.  We allow one extra logical nesting level, since this group
		 * will eventually be wrapped in an outer "Workers" group.
		 */
		ExplainOpenSetAsideGroup("Worker", NULL, true, 2, es);

		/*
		 * In non-TEXT formats we always emit a "Worker Number" field, even if
		 * there's no other data for this worker.
		 */
		if (es->format != EXPLAIN_FORMAT_TEXT)
			ExplainPropertyInteger("Worker Number", NULL, n, es);

		wstate->worker_inited[n] = true;
	}
	else
	{
		/* Resuming output for a worker we've already emitted some data for */
		es->str = &wstate->worker_str[n];

		/* Restore formatting state saved by last ExplainCloseWorker() */
		ExplainRestoreGroup(es, 2, &wstate->worker_state_save[n]);
	}

	/*
	 * In TEXT format, prefix the first output line for this worker with
	 * "Worker N:".  Then, any additional lines should be indented one more
	 * stop than the "Worker N" line is.
	 */
	if (es->format == EXPLAIN_FORMAT_TEXT)
	{
		if (es->str->len == 0)
		{
			ExplainIndentText(es);
			appendStringInfo(es->str, "Worker %d:  ", n);
		}

		es->indent++;
	}
}