Oracle Result Cache

result cache

1.结果集缓存，oracle 11g新功能，可以在服务器以及客户端缓存结果集，

服务器端可以通过参数

sql query result cache:存储sql查询结果集

PL/SQL Function Result Cache:用于存储PL/SQL函数结果集

2.result cache 相关参数设置

如果result_cache_mode 设置为MANUAL 时，需要通过手工指定来实现，hints 是result_cache

注意：参数设置为auto时，只有在结果集已经存在的情况下才会直接查询结果集，

如果结果集不存在，则不会自动创建

 

相关参数设置

 

SQL> select  a.VALUE,a.NAME from v$parameter a where a.NAME like '%result%';

 

cache 的对象

SQL> select  type,name  from v$result_cache_objects;

TYPE       NAME

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

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

Dependency SCOTT.DEPT

Dependency SCOTT.EMP

Result     select /*+ result_cache */  empno,ename,dname from scott.emp e,scott.dept d where d.deptno = e.deptno

Result     select /*+ result_cache */  empno,ename from scott.emp

Result     select /*+ result_cache */ * from scott.emp

Result     select /*+ result_cache */ count(1) from scott.emp

 

3.测试结果集

SQL>  select /*+ result_cache */  empno,ename from scott.emp;

已选择14行。

执行计划

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

Plan hash value: 3956160932

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

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

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

|   0 | SELECT STATEMENT   |                            |    14 |   140 |     2   (0)| 00:00:01 |

|   1 |  RESULT CACHE      | dhf4gu6spq6tjbu3f8pu4y3652 |       |       |            |          |

|   2 |   TABLE ACCESS FULL| EMP                        |    14 |   140 |     2   (0)| 00:00:01 |

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

Result Cache Information (identified by operation id):

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

   1 - column-count=2; dependencies=(SCOTT.EMP); name="select /*+ result_cache */  empno,ename from scott.emp"

统计信息

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

          1  recursive calls

          0  db block gets

          4  consistent gets

          0  physical reads

          0  redo size

        612  bytes sent via SQL*Net to client

        408  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

         14  rows processed

再次查询

SQL>  select /*+ result_cache */  empno,ename from scott.emp;

已选择14行。

执行计划

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

Plan hash value: 3956160932

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

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

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

|   0 | SELECT STATEMENT   |                            |    14 |   140 |     2   (0)| 00:00:01 |

|   1 |  RESULT CACHE      | dhf4gu6spq6tjbu3f8pu4y3652 |       |       |            |          |

|   2 |   TABLE ACCESS FULL| EMP                        |    14 |   140 |     2   (0)| 00:00:01 |

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

Result Cache Information (identified by operation id):

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

   1 - column-count=2; dependencies=(SCOTT.EMP); name="select /*+ result_cache */  empno,ename from scott.emp"

统计信息

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

          0  recursive calls

          0  db block gets

          0  consistent gets

          0  physical reads

          0  redo size

        612  bytes sent via SQL*Net to client

        408  bytes received via SQL*Net from client

          2  SQL*Net roundtrips to/from client

          0  sorts (memory)

          0  sorts (disk)

         14  rows processed

其逻辑读降为0，即直接从缓冲结果集获取数据