Function cdbpath_create_motion_path

src/backend/cdb/cdbpath.c:192–666

* cdbpath_create_motion_path * Returns a Path that delivers the subpath result to the * given locus, or NULL if it can't be done. * * 'pathkeys' must specify an ordering equal to or weaker than the * subpath's existing ordering. * * If no motion is needed, the caller's subpath is returned unchanged. * Else if require_existing_order is true, NULL is returned if the *

 *      pathkeys otherwise (the usual case).
 */
Path *
cdbpath_create_motion_path(PlannerInfo *root,
						   Path *subpath,
						   List *pathkeys,
						   bool require_existing_order,
						   CdbPathLocus locus)
{
	CdbMotionPath *pathnode;

	Assert(cdbpathlocus_is_valid(locus) &&
		   cdbpathlocus_is_valid(subpath->locus));

	/*
	 * ISTM, subpath of ReplicatedWorkers only happened if general join with broadcast.
	 * And that only happened if we're doing some updating. Such as:
	 * `explain update rt3 set b = rt2.b from rt2 where rt3.b = rt2.b;`
	 * where rt3 and rt2 should have different numsegments.
	 * However, we don't support parallel update yet, so it will never happen.
	 */
	Assert(!CdbPathLocus_IsReplicatedWorkers(subpath->locus));

	/*
	 * Motion is to change path's locus, if target locus is the
	 * same as the subpath's, there is no need to add motion.
	 */
	if (cdbpathlocus_equal(subpath->locus, locus))
		return subpath;

	/* Moving subpath output to a single executor process (qDisp or qExec)? */
	if (CdbPathLocus_IsOuterQuery(locus))
	{
		/* Outer -> Outer is a no-op */
		if (CdbPathLocus_IsOuterQuery(subpath->locus))
		{
			return subpath;
		}

		if (CdbPathLocus_IsGeneral(subpath->locus))
		{
			/* XXX: this is a bit bogus. We just change the subpath's locus. */
			subpath->locus = locus;
			return subpath;
		}

		if (CdbPathLocus_IsEntry(subpath->locus) ||
			CdbPathLocus_IsSingleQE(subpath->locus))
		{
			/*
			 * XXX: this is a bit bogus. We just change the subpath's locus.
			 *
			 * This is also bogus, because the outer query might need to run
			 * in segments.
			 */
			subpath->locus = locus;
			return subpath;
		}
	}
	else if (CdbPathLocus_IsBottleneck(locus))