Function create_partial_window_path

src/backend/optimizer/plan/planner.c:9148–9212

* Parallel processing of window functions. * * NB: it may produce non-deterministic results if the window function * lacks ORDER BY and PARTITION BY clause. * SQL:2011 has clarified this behavior. */

 * SQL:2011 has clarified this behavior.
 */
static void
create_partial_window_path(PlannerInfo *root,
					   RelOptInfo *window_rel,
					   Path *path,
					   PathTarget *input_target,
					   PathTarget *output_target,
					   WindowFuncLists *wflists,
					   List *activeWindows)
{
	PathTarget *window_target;
	ListCell   *l;

	window_target = input_target;

	foreach(l, activeWindows)
	{
		WindowClause *wc = lfirst_node(WindowClause, l);
		List	   *window_pathkeys;
		int			presorted_keys;
		bool		is_sorted;

		window_pathkeys = make_pathkeys_for_window(root,
												   wc,
												   root->processed_tlist);

		is_sorted = pathkeys_count_contained_in(window_pathkeys,
												path->pathkeys,
												&presorted_keys);

		path = cdb_prepare_path_for_sorted_agg(root,
											   is_sorted,
											   presorted_keys,
											   window_rel,
											   path,
											   path->pathtarget,
											   window_pathkeys,
											   -1.0,
											   wc->partitionClause,
											   NIL);
		if (lnext(activeWindows, l))
		{
			ListCell   *lc2;

			window_target = copy_pathtarget(window_target);
			foreach(lc2, wflists->windowFuncs[wc->winref])
			{
				WindowFunc *wfunc = lfirst_node(WindowFunc, lc2);

				add_column_to_pathtarget(window_target, (Expr *) wfunc, 0);
				window_target->width += get_typavgwidth(wfunc->wintype, -1);
			}
		}
		else
		{
			window_target = output_target;
		}

		path = (Path *)