SQL逻辑读变成零

使用缓存HINT 让逻辑读变成0.

create table t as select * from dba_objects;

insert into t select * from t;

commit;

set autotrace on

set timing on

set linesize 1000

select /*+ result_cache */ count(*) from t;

---接下来再次执行(居然发现逻辑读为0）：

set autotrace on

select /*+ result_cache */ count(*) from t;

执行计划：

SQL> set autotrace on

SQL> select /*+ result_cache */ count(*) from t;

  COUNT(*)

----------

    145762

已用时间:  00: 00: 00.01

执行计划

------------------------------------------------------------------------------------------

| Id  | Operation           | Name                       | Rows  | Cost (%CPU)| Time     |

------------------------------------------------------------------------------------------

|   0 | SELECT STATEMENT    |                            |     1 |   589   (1)| 00:00:08 |

|   1 |  RESULT CACHE       | d827qx1jmwjc86yqynrp1kvpny |       |            |          |

|   2 |   SORT AGGREGATE    |                            |     1 |            |          |

|   3 |    TABLE ACCESS FULL| T                          |   277K|   589   (1)| 00:00:08 |

------------------------------------------------------------------------------------------

统计信息

----------------------------------------------------------

            recursive calls

            db block gets

            consistent gets

          0  physical reads

          0  redo size

        425  bytes sent via SQL*Net to client

        416  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

          1  rows processed