Function ExecAppendAsyncBegin

src/backend/executor/nodeAppend.c:901–948

---------------------------------------------------------------- * ExecAppendAsyncBegin * * Begin executing designed async-capable subplans. * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
static void
ExecAppendAsyncBegin(AppendState *node)
{
	int			i;

	/* Backward scan is not supported by async-aware Appends. */
	Assert(ScanDirectionIsForward(node->ps.state->es_direction));

	/* We should never be called when there are no subplans */
	Assert(node->as_nplans > 0);

	/* We should never be called when there are no async subplans. */
	Assert(node->as_nasyncplans > 0);

	/* If we've yet to determine the valid subplans then do so now. */
	if (node->as_valid_subplans == NULL)
	{
		Append	*plan = (Append *) node->ps.plan;
		node->as_valid_subplans =
			ExecFindMatchingSubPlans(node->as_prune_state,
										 node->ps.state,
										 list_length(plan->appendplans),
										 plan->join_prune_paramids);

		classify_matching_subplans(node);
	}

	/* Initialize state variables. */
	node->as_syncdone = bms_is_empty(node->as_valid_subplans);
	node->as_nasyncremain = bms_num_members(node->as_valid_asyncplans);

	/* Nothing to do if there are no valid async subplans. */
	if (node->as_nasyncremain == 0)
		return;

	/* Make a request for each of the valid async subplans. */
	i = -1;
	while ((i = bms_next_member(node->as_valid_asyncplans, i)) >= 0)
	{
		AsyncRequest *areq = node->as_asyncrequests[i];

		Assert(areq->request_index == i);
		Assert(!areq->callback_pending);

		/* Do the actual work. */
		ExecAsyncRequest(areq);
	}
}

/* ----------------------------------------------------------------
 *		ExecAppendAsyncGetNext