Function GetExistingLocalJoinPath

src/backend/foreign/foreign.c:1019–1105

* Get a copy of an existing local path for a given join relation. * * This function is usually helpful to obtain an alternate local path for EPQ * checks. * * Right now, this function only supports unparameterized foreign joins, so we * only search for unparameterized path in the given list of paths. Since we * are searching for a path which can be used to construct an alternative local *

 * choose the most efficient path, which is all for the best.
 */
Path *
GetExistingLocalJoinPath(RelOptInfo *joinrel)
{
	ListCell   *lc;

	Assert(IS_JOIN_REL(joinrel));

	foreach(lc, joinrel->pathlist)
	{
		Path	   *path = (Path *) lfirst(lc);
		JoinPath   *joinpath = NULL;

		/* Skip parameterized paths. */
		if (path->param_info != NULL)
			continue;

		switch (path->pathtype)
		{
			case T_HashJoin:
				{
					HashPath   *hash_path = makeNode(HashPath);

					memcpy(hash_path, path, sizeof(HashPath));
					joinpath = (JoinPath *) hash_path;
				}
				break;

			case T_NestLoop:
				{
					NestPath   *nest_path = makeNode(NestPath);

					memcpy(nest_path, path, sizeof(NestPath));
					joinpath = (JoinPath *) nest_path;
				}
				break;

			case T_MergeJoin:
				{
					MergePath  *merge_path = makeNode(MergePath);

					memcpy(merge_path, path, sizeof(MergePath));
					joinpath = (JoinPath *) merge_path;
				}
				break;

			default:

				/*
				 * Just skip anything else. We don't know if corresponding
				 * plan would build the output row from whole-row references
				 * of base relations and execute the EPQ checks.
				 */
				break;
		}

		/* This path isn't good for us, check next. */
		if (!joinpath)
			continue;