Function CdbMergeComparator

src/backend/executor/nodeMotion.c:1038–1082

* CdbMergeComparator: * Used to compare tuples for a sorted motion node. */

 * Used to compare tuples for a sorted motion node.
 */
static int
CdbMergeComparator(Datum lhs, Datum rhs, void *context)
{
	MotionState *node = (MotionState *) context;
	int			lSegIdx = DatumGetInt32(lhs);
	int			rSegIdx = DatumGetInt32(rhs);

	TupleTableSlot *lslot = node->slots[lSegIdx];
	TupleTableSlot *rslot = node->slots[rSegIdx];
	SortSupport	sortKeys = node->sortKeys;
	int			nkey;
	int			compare;

	Assert(lslot && rslot);

	for (nkey = 0; nkey < node->numSortCols; nkey++)
	{
		SortSupport ssup = &sortKeys[nkey];
		AttrNumber	attno = ssup->ssup_attno;
		Datum		datum1,
					datum2;
		bool		isnull1,
					isnull2;

		/*
		 * The caller has called slot_getsomeattrs() to ensure
		 * that all the columns we need are available directly in
		 * the values/isnull arrays.
		 */
		datum1 = lslot->tts_values[attno - 1];
		isnull1 = lslot->tts_isnull[attno - 1];
		datum2 = rslot->tts_values[attno - 1];
		isnull2 = rslot->tts_isnull[attno - 1];

		compare = ApplySortComparator(datum1, isnull1,
									  datum2, isnull2,
									  ssup);
		if (compare != 0)
		{
			INVERT_COMPARE_RESULT(compare);
			return compare;
		}
	}
	return 0;
}								/* CdbMergeComparator */

/*
 * Experimental code that will be replaced later with new hashing mechanism