Function IndexNextWithReorder

src/backend/executor/nodeIndexscan.c:171–358

---------------------------------------------------------------- * IndexNextWithReorder * * Like IndexNext, but this version can also re-check ORDER BY * expressions, and reorder the tuples as necessary. * ---------------------------------------------------------------- */

 * ----------------------------------------------------------------
 */
static TupleTableSlot *
IndexNextWithReorder(IndexScanState *node)
{
	EState	   *estate;
	ExprContext *econtext;
	IndexScanDesc scandesc;
	TupleTableSlot *slot;
	ReorderTuple *topmost = NULL;
	bool		was_exact;
	Datum	   *lastfetched_vals;
	bool	   *lastfetched_nulls;
	int			cmp;

	estate = node->ss.ps.state;

	/*
	 * Only forward scan is supported with reordering.  Note: we can get away
	 * with just Asserting here because the system will not try to run the
	 * plan backwards if ExecSupportsBackwardScan() says it won't work.
	 * Currently, that is guaranteed because no index AMs support both
	 * amcanorderbyop and amcanbackward; if any ever do,
	 * ExecSupportsBackwardScan() will need to consider indexorderbys
	 * explicitly.
	 */
	Assert(!ScanDirectionIsBackward(((IndexScan *) node->ss.ps.plan)->indexorderdir));
	Assert(ScanDirectionIsForward(estate->es_direction));

	scandesc = node->iss_ScanDesc;
	econtext = node->ss.ps.ps_ExprContext;
	slot = node->ss.ss_ScanTupleSlot;

	if (scandesc == NULL)
	{
		/*
		 * We reach here if the index scan is not parallel, or if we're
		 * serially executing an index scan that was planned to be parallel.
		 */
		scandesc = index_beginscan(node->ss.ss_currentRelation,
								   node->iss_RelationDesc,
								   estate->es_snapshot,
								   node->iss_NumScanKeys,
								   node->iss_NumOrderByKeys);

		node->iss_ScanDesc = scandesc;

		/*
		 * If no run-time keys to calculate or they are ready, go ahead and
		 * pass the scankeys to the index AM.
		 */
		if (node->iss_NumRuntimeKeys == 0 || node->iss_RuntimeKeysReady)
			index_rescan(scandesc,
						 node->iss_ScanKeys, node->iss_NumScanKeys,
						 node->iss_OrderByKeys, node->iss_NumOrderByKeys);
	}

	for (;;)
	{
		CHECK_FOR_INTERRUPTS();