func (ls *LocalDisttaeDataSource) handleOrderBy() {
 	// for ordered scan, sort blocklist by zonemap info, and then filter by zonemap
-	if len(ls.OrderBy) > 0 && ls.Limit == 0 {
+	if len(ls.OrderBy) > 0 {
+		// if order by expression is a function call, we can't use zonemap to sort blocks.
+		// This is the case for vector index scans.
+		if ls.OrderBy[0].Expr.GetF() != nil {
+			return
+		}
+
 		if !ls.sorted {
 			ls.desc = ls.OrderBy[0].Flag&plan.OrderBySpec_DESC != 0
 			ls.getBlockZMs()
 			ls.sortBlockList()
 			ls.sorted = true
 		}
 		i := ls.rangesCursor
 		sliceLen := ls.rangeSlice.Len()
 		for i < sliceLen {
 			if ls.needReadBlkByZM(i) {
 				break
 			}
 			i++
 		}
 		ls.rangesCursor = i
 	}
 }

-		if scanNode.Stats.Selectivity < 0.5 {
-			newblockNum := int32(limitVal / 2)
-			if newblockNum < scanNode.Stats.BlockNum {
-				scanNode.Stats.BlockNum = newblockNum
-			}
-		} else {
-			scanNode.Stats.BlockNum = 1
-		}
+		// After pushdown, the number of blocks to be scanned is still determined by the number of probes,
+		// so we don't need to adjust the BlockNum.
+		// The Outcnt is already updated to reflect the limit.

 	sql := fmt.Sprintf(
 		"SELECT `%s`, %s(`%s`, '%s') as vec_dist FROM `%s`.`%s` WHERE `%s` = %d AND `%s` IN (%s) ORDER BY vec_dist LIMIT %d",
 		catalog.SystemSI_IVFFLAT_TblCol_Entries_pk,
 		metric.MetricTypeToDistFuncName[metric.MetricType(idxcfg.Ivfflat.Metric)],
 		catalog.SystemSI_IVFFLAT_TblCol_Entries_entry,
 		types.ArrayToString(query),
 		tblcfg.DbName, tblcfg.EntriesTable,
 		catalog.SystemSI_IVFFLAT_TblCol_Entries_version,
 		idx.Version,
 		catalog.SystemSI_IVFFLAT_TblCol_Entries_id,
 		instr,
 		rt.Limit,
 	)
 
-	fmt.Println("IVFFlat SQL: ", sql)
-