5-3-3. 언제까지 인덱스를 사용할 것인가?

-- [SQL-5-3-3-a] EXPLAIN (ANALYZE,BUFFERS,COSTS OFF) SELECT /*+ IndexScan(t1 tr_ord_big_x01) */ t1.* FROM startdbpg.tr_ord_big t1 WHERE t1.ord_dtm >= '2019-03-01'::date AND t1.ord_dtm < '2020-01-01'::date;