Function try_mergejoin_path

src/backend/optimizer/path/joinpath.c:928–1021

* try_mergejoin_path * Consider a merge join path; if it appears useful, push it into * the joinrel's pathlist via add_path(). */

 *	  the joinrel's pathlist via add_path().
 */
static void
try_mergejoin_path(PlannerInfo *root,
				   RelOptInfo *joinrel,
				   Path *outer_path,
				   Path *inner_path,
				   List *pathkeys,
				   List *mergeclauses,
				   List *outersortkeys,
				   List *innersortkeys,
				   JoinType jointype,
				   JoinType orig_jointype,
				   JoinPathExtraData *extra,
				   bool is_partial)
{
	Relids		required_outer;
	JoinCostWorkspace workspace;

	if (is_partial)
	{
		try_partial_mergejoin_path(root,
								   joinrel,
								   outer_path,
								   inner_path,
								   pathkeys,
								   mergeclauses,
								   outersortkeys,
								   innersortkeys,
								   jointype,
								   orig_jointype,
								   extra);
		return;
	}

	/*
	 * Check to see if proposed path is still parameterized, and reject if the
	 * parameterization wouldn't be sensible.
	 */
	required_outer = calc_non_nestloop_required_outer(outer_path,
													  inner_path);
	if (required_outer &&
		!bms_overlap(required_outer, extra->param_source_rels))
	{
		/* Waste no memory when we reject a path here */
		bms_free(required_outer);
		return;
	}

	/*
	 * If the given paths are already well enough ordered, we can skip doing
	 * an explicit sort.
	 */
	if (outersortkeys &&
		pathkeys_contained_in(outersortkeys, outer_path->pathkeys))
		outersortkeys = NIL;
	if (innersortkeys &&
		pathkeys_contained_in(innersortkeys, inner_path->pathkeys))
		innersortkeys = NIL;