Function choose_next_subplan_for_worker

src/backend/executor/nodeAppend.c:727–846

---------------------------------------------------------------- * choose_next_subplan_for_worker * * Choose next subplan for a parallel-aware Append, returning * false if there are no more. * * We start from the first plan and advance through the list; * when we get back to the end, we loop back to the first * partial plan. This assigns the non-partial plans first in * order of d

 * ----------------------------------------------------------------
 */
static bool
choose_next_subplan_for_worker(AppendState *node)
{
	ParallelAppendState *pstate = node->as_pstate;

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

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

	LWLockAcquire(&pstate->pa_lock, LW_EXCLUSIVE);

	/* Mark just-completed subplan as finished. */
	if (node->as_whichplan != INVALID_SUBPLAN_INDEX)
		node->as_pstate->pa_finished[node->as_whichplan] = true;

	/*
	 * If we've yet to determine the valid subplans then do so now.  If
	 * run-time pruning is disabled then the valid subplans will always be set
	 * to all subplans.
	 */
	else 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);
		mark_invalid_subplans_as_finished(node);
	}

	/* If all the plans are already done, we have nothing to do */
	if (pstate->pa_next_plan == INVALID_SUBPLAN_INDEX)
	{
		LWLockRelease(&pstate->pa_lock);
		return false;
	}

	/* Save the plan from which we are starting the search. */
	node->as_whichplan = pstate->pa_next_plan;

	/* Loop until we find a valid subplan to execute. */
	while (pstate->pa_finished[pstate->pa_next_plan])
	{
		int			nextplan;

		nextplan = bms_next_member(node->as_valid_subplans,
								   pstate->pa_next_plan);
		if (nextplan >= 0)
		{
			/* Advance to the next valid plan. */
			pstate->pa_next_plan = nextplan;
		}
		else if (node->as_whichplan > node->as_first_partial_plan)
		{