Function postgresGetForeignUpperPaths

contrib/postgres_fdw/postgres_fdw.c:6413–6457

* postgresGetForeignUpperPaths * Add paths for post-join operations like aggregation, grouping etc. if * corresponding operations are safe to push down. */

 *		corresponding operations are safe to push down.
 */
static void
postgresGetForeignUpperPaths(PlannerInfo *root, UpperRelationKind stage,
							 RelOptInfo *input_rel, RelOptInfo *output_rel,
							 void *extra)
{
	PgFdwRelationInfo *fpinfo;

	/*
	 * If input rel is not safe to pushdown, then simply return as we cannot
	 * perform any post-join operations on the foreign server.
	 */
	if (!input_rel->fdw_private ||
		!((PgFdwRelationInfo *) input_rel->fdw_private)->pushdown_safe)
		return;

	/* Ignore stages we don't support; and skip any duplicate calls. */
	if ((stage != UPPERREL_GROUP_AGG &&
		 stage != UPPERREL_ORDERED &&
		 stage != UPPERREL_FINAL) ||
		output_rel->fdw_private)
		return;

	fpinfo = (PgFdwRelationInfo *) palloc0(sizeof(PgFdwRelationInfo));
	fpinfo->pushdown_safe = false;
	fpinfo->stage = stage;
	output_rel->fdw_private = fpinfo;

	switch (stage)
	{
		case UPPERREL_GROUP_AGG:
			add_foreign_grouping_paths(root, input_rel, output_rel,
									   (GroupPathExtraData *) extra);
			break;
		case UPPERREL_ORDERED:
			add_foreign_ordered_paths(root, input_rel, output_rel);
			break;
		case UPPERREL_FINAL:
			add_foreign_final_paths(root, input_rel, output_rel,
									(FinalPathExtraData *) extra);
			break;
		default:
			elog(ERROR, "unexpected upper relation: %d", (int) stage);
			break;
	}
}

/*
 * add_foreign_grouping_paths