Function postgresGetForeignJoinPaths

contrib/postgres_fdw/postgres_fdw.c:6034–6168

* postgresGetForeignJoinPaths * Add possible ForeignPath to joinrel, if join is safe to push down. */

 *		Add possible ForeignPath to joinrel, if join is safe to push down.
 */
static void
postgresGetForeignJoinPaths(PlannerInfo *root,
							RelOptInfo *joinrel,
							RelOptInfo *outerrel,
							RelOptInfo *innerrel,
							JoinType jointype,
							JoinPathExtraData *extra)
{
	PgFdwRelationInfo *fpinfo;
	ForeignPath *joinpath;
	double		rows;
	int			width;
	Cost		startup_cost;
	Cost		total_cost;
	Path	   *epq_path;		/* Path to create plan to be executed when
								 * EvalPlanQual gets triggered. */

	/*
	 * Skip if this join combination has been considered already.
	 */
	if (joinrel->fdw_private)
		return;

	/*
	 * This code does not work for joins with lateral references, since those
	 * must have parameterized paths, which we don't generate yet.
	 */
	if (!bms_is_empty(joinrel->lateral_relids))
		return;

	/*
	 * Create unfinished PgFdwRelationInfo entry which is used to indicate
	 * that the join relation is already considered, so that we won't waste
	 * time in judging safety of join pushdown and adding the same paths again
	 * if found safe. Once we know that this join can be pushed down, we fill
	 * the entry.
	 */
	fpinfo = (PgFdwRelationInfo *) palloc0(sizeof(PgFdwRelationInfo));
	fpinfo->pushdown_safe = false;
	joinrel->fdw_private = fpinfo;
	/* attrs_used is only for base relations. */
	fpinfo->attrs_used = NULL;

	/*
	 * If there is a possibility that EvalPlanQual will be executed, we need
	 * to be able to reconstruct the row using scans of the base relations.
	 * GetExistingLocalJoinPath will find a suitable path for this purpose in
	 * the path list of the joinrel, if one exists.  We must be careful to
	 * call it before adding any ForeignPath, since the ForeignPath might
	 * dominate the only suitable local path available.  We also do it before
	 * calling foreign_join_ok(), since that function updates fpinfo and marks
	 * it as pushable if the join is found to be pushable.
	 */
	if (root->parse->commandType == CMD_DELETE ||
		root->parse->commandType == CMD_UPDATE ||
		root->rowMarks)
	{
		epq_path = GetExistingLocalJoinPath(joinrel);