Function fetch_upper_rel

src/backend/optimizer/util/relnode.c:1646–1686

* fetch_upper_rel * Build a RelOptInfo describing some post-scan/join query processing, * or return a pre-existing one if somebody already built it. * * An "upper" relation is identified by an UpperRelationKind and a Relids set. * The meaning of the Relids set is not specified here, and very likely will * vary for different relation kinds. * * Most of the fields in an upper-level RelOptI

 * care about fields that are of interest to add_path() and set_cheapest().
 */
RelOptInfo *
fetch_upper_rel(PlannerInfo *root, UpperRelationKind kind, Relids relids)
{
	RelOptInfo *upperrel;
	ListCell   *lc;

	/*
	 * For the moment, our indexing data structure is just a List for each
	 * relation kind.  If we ever get so many of one kind that this stops
	 * working well, we can improve it.  No code outside this function should
	 * assume anything about how to find a particular upperrel.
	 */

	/* If we already made this upperrel for the query, return it */
	foreach(lc, root->upper_rels[kind])
	{
		upperrel = (RelOptInfo *) lfirst(lc);

		if (bms_equal(upperrel->relids, relids))
			return upperrel;
	}

	upperrel = makeNode(RelOptInfo);
	upperrel->reloptkind = RELOPT_UPPER_REL;
	upperrel->relids = bms_copy(relids);

	/* cheap startup cost is interesting iff not all tuples to be retrieved */
	upperrel->consider_startup = (root->tuple_fraction > 0);
	upperrel->consider_param_startup = false;
	upperrel->consider_parallel = false;	/* might get changed later */
	upperrel->reltarget = create_empty_pathtarget();
	upperrel->pathlist = NIL;
	upperrel->cheapest_startup_path = NULL;
	upperrel->cheapest_total_path = NULL;
	upperrel->cheapest_unique_path = NULL;
	upperrel->cheapest_parameterized_paths = NIL;

	root->upper_rels[kind] = lappend(root->upper_rels[kind], upperrel);

	return upperrel;
}


/*