Function reparameterize_path_by_child

src/backend/optimizer/util/pathnode.c:6329–6601

* reparameterize_path_by_child * Given a path parameterized by the parent of the given child relation, * translate the path to be parameterized by the given child relation. * * The function creates a new path of the same type as the given path, but * parameterized by the given child relation. Most fields from the original * path can simply be flat-copied, but any expressions must be adj

 * If the given path can not be reparameterized, the function returns NULL.
 */
Path *
reparameterize_path_by_child(PlannerInfo *root, Path *path,
							 RelOptInfo *child_rel)
{

#define FLAT_COPY_PATH(newnode, node, nodetype)  \
	( (newnode) = makeNode(nodetype), \
	  memcpy((newnode), (node), sizeof(nodetype)) )

#define ADJUST_CHILD_ATTRS(node) \
	((node) = \
	 (List *) adjust_appendrel_attrs_multilevel(root, (Node *) (node), \
												child_rel->relids, \
												child_rel->top_parent_relids))

#define REPARAMETERIZE_CHILD_PATH(path) \
do { \
	(path) = reparameterize_path_by_child(root, (path), child_rel); \
	if ((path) == NULL) \
		return NULL; \
} while(0)

#define REPARAMETERIZE_CHILD_PATH_LIST(pathlist) \
do { \
	if ((pathlist) != NIL) \
	{ \
		(pathlist) = reparameterize_pathlist_by_child(root, (pathlist), \
													  child_rel); \
		if ((pathlist) == NIL) \
			return NULL; \
	} \
} while(0)

	Path	   *new_path;
	ParamPathInfo *new_ppi;
	ParamPathInfo *old_ppi;
	Relids		required_outer;

	/*
	 * If the path is not parameterized by parent of the given relation, it
	 * doesn't need reparameterization.
	 */
	if (!path->param_info ||
		!bms_overlap(PATH_REQ_OUTER(path), child_rel->top_parent_relids))
		return path;

	/*
	 * If possible, reparameterize the given path, making a copy.
	 *
	 * This function is currently only applied to the inner side of a nestloop
	 * join that is being partitioned by the partitionwise-join code.  Hence,
	 * we need only support path types that plausibly arise in that context.
	 * (In particular, supporting sorted path types would be a waste of code
	 * and cycles: even if we translated them here, they'd just lose in
	 * subsequent cost comparisons.)  If we do see an unsupported path type,
	 * that just means we won't be able to generate a partitionwise-join plan
	 * using that path type.
	 */