Function accumulate_append_subpath

src/backend/optimizer/path/allpaths.c:2341–2378

* accumulate_append_subpath * Add a subpath to the list being built for an Append or MergeAppend. * * It's possible that the child is itself an Append or MergeAppend path, in * which case we can "cut out the middleman" and just add its child paths to * our own list. (We don't try to do this earlier because we need to apply * both levels of transformation to the quals.) * * Note that if w

 * paths).
 */
static void
accumulate_append_subpath(Path *path, List **subpaths, List **special_subpaths)
{
	if (IsA(path, AppendPath))
	{
		AppendPath *apath = (AppendPath *) path;

		if (!apath->path.parallel_aware || apath->first_partial_path == 0)
		{
			*subpaths = list_concat(*subpaths, apath->subpaths);
			return;
		}
		else if (special_subpaths != NULL)
		{
			List	   *new_special_subpaths;

			/* Split Parallel Append into partial and non-partial subpaths */
			*subpaths = list_concat(*subpaths,
									list_copy_tail(apath->subpaths,
												   apath->first_partial_path));
			new_special_subpaths =
				list_truncate(list_copy(apath->subpaths),
							  apath->first_partial_path);
			*special_subpaths = list_concat(*special_subpaths,
											new_special_subpaths);
			return;
		}
	}
	else if (IsA(path, MergeAppendPath))
	{
		MergeAppendPath *mpath = (MergeAppendPath *) path;

		*subpaths = list_concat(*subpaths, mpath->subpaths);
		return;
	}

	*subpaths = lappend(*subpaths, path);
}

/*
 * get_singleton_append_subpath