Function try_partial_nestloop_path

src/backend/optimizer/path/joinpath.c:835–921

* try_partial_nestloop_path * Consider a partial nestloop join path; if it appears useful, push it into * the joinrel's partial_pathlist via add_partial_path(). */

 *	  the joinrel's partial_pathlist via add_partial_path().
 */
static void
try_partial_nestloop_path(PlannerInfo *root,
						  RelOptInfo *joinrel,
						  Path *outer_path,
						  Path *inner_path,
						  List *pathkeys,
						  JoinType jointype,
						  JoinType orig_jointype,
						  JoinPathExtraData *extra)
{
	JoinCostWorkspace workspace;
	Path	*nestloop_path;

	/*
	 * If the inner path is parameterized, the parameterization must be fully
	 * satisfied by the proposed outer path.  Parameterized partial paths are
	 * not supported.  The caller should already have verified that no lateral
	 * rels are required here.
	 */
	Assert(bms_is_empty(joinrel->lateral_relids));
	if (inner_path->param_info != NULL)
	{
		Relids		inner_paramrels = inner_path->param_info->ppi_req_outer;
		RelOptInfo *outerrel = outer_path->parent;
		Relids		outerrelids;

		/*
		 * The inner and outer paths are parameterized, if at all, by the top
		 * level parents, not the child relations, so we must use those relids
		 * for our parameterization tests.
		 */
		if (outerrel->top_parent_relids)
			outerrelids = outerrel->top_parent_relids;
		else
			outerrelids = outerrel->relids;

		if (!bms_is_subset(inner_paramrels, outerrelids))
			return;
	}

	/*
	 * Before creating a path, get a quick lower bound on what it is likely to
	 * cost.  Bail out right away if it looks terrible.
	 */
	initial_cost_nestloop(root, &workspace, jointype,
						  outer_path, inner_path, extra);
	if (!add_partial_path_precheck(joinrel, workspace.total_cost, pathkeys))
		return;

	/*
	 * If the inner path is parameterized, it is parameterized by the topmost
	 * parent of the outer rel, not the outer rel itself.  Fix that.
	 */
	if (PATH_PARAM_BY_PARENT(inner_path, outer_path->parent))
	{
		inner_path = reparameterize_path_by_child(root, inner_path,
												  outer_path->parent);