3.解释执行计划的方法

2013-08-06

－－－－－－－－－－－－－－解释执行计划的方法－－－－－－－－－－－－－－－－－－－－－－－－－－－－

用autotrace前提：

SQL> @/u01/oracle/product/10.2.0/db_1/sqlplus/admin/plustrce.sql  --sys用户下执行

SQL>

SQL> drop role plustrace;

drop role plustrace

         *

ERROR at line 1:

ORA-01919: role 'PLUSTRACE' does not exist

SQL> create role plustrace;

Role created.

SQL> grant select on v_$sesstat to plustrace;

Grant succeeded.

SQL> grant select on v_$statname to plustrace;

Grant succeeded.

SQL> grant select on v_$mystat to plustrace;

Grant succeeded.

SQL> grant plustrace to dba with admin option;

Grant succeeded.

SQL> set echo off

SQL> grant plustrace to scott;  －－将权限授予SCOTT可以用autotrace

Grant succeeded.

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

1、autotrace工具详解

SQL> set autotrace off   ——默认情况下是关闭的

SQL> set autotrace on exp         －－显示查询结果、执行计划

SQL> select * from t where rownum=1;

OWNER                          OBJECT_TYPE

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

PUBLIC                         SYNONYM

Execution Plan

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

Plan hash value: 508354683

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

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

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

|   0 | SELECT STATEMENT   |      |     1 |    28 |     2   (0)| 00:00:01 |

|*  1 |  COUNT STOPKEY     |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| T    | 45659 |  1248K|     2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

  1 - filter(ROWNUM=1)

Note

-----

  - dynamic sampling used for this statement

SQL> set autotrace on            --显示查询结果、执行计划、执行的物理统计信息

SQL> select * from t where rownum=1;

OBJECT_NAME                    OBJECT_TYPE

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

DUAL                           TABLE

Execution Plan

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

Plan hash value: 508354683

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

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

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

|   0 | SELECT STATEMENT   |      |     1 |    28 |     2   (0)| 00:00:01 |

|*  1 |  COUNT STOPKEY     |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| T    | 43751 |  1196K|     2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

  1 - filter(ROWNUM=1)

Note

-----

  - dynamic sampling used for this statement

Statistics

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

        71  recursive calls

         0  db block gets

       146  consistent gets

       155  physical reads

         0  redo size

       483  bytes sent via SQL*Net to client

       400  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

         0  sorts (memory)

         0  sorts (disk)

         1  rows processed

SQL> set autotrace on stat   －－显示查询结果、执行的物理统计信息

SQL> select * from t where rownum=1;

OBJECT_NAME                    OBJECT_TYPE

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

DUAL                           TABLE

Statistics

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

         0  recursive calls

         0  db block gets

         4  consistent gets

         0  physical reads

         0  redo size

       483  bytes sent via SQL*Net to client

       400  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

         0  sorts (memory)

         0  sorts (disk)

         1  rows processed

SQL> set autotrace trace exp   －－显示执行计划

SQL> select * from t where rownum=1;

Execution Plan

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

Plan hash value: 508354683

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

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

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

|   0 | SELECT STATEMENT   |      |     1 |    28 |     2   (0)| 00:00:01 |

|*  1 |  COUNT STOPKEY     |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| T    | 43751 |  1196K|     2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

  1 - filter(ROWNUM=1)

Note

-----

  - dynamic sampling used for this statement

SQL> set autotrace trace exp stat  －－显示执行计划和物理统计信息

SQL> select * from t where rownum=1;

Execution Plan

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

Plan hash value: 508354683

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

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

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

|   0 | SELECT STATEMENT   |      |     1 |    28 |     2   (0)| 00:00:01 |

|*  1 |  COUNT STOPKEY     |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| T    | 43751 |  1196K|     2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

  1 - filter(ROWNUM=1)

Note

-----

  - dynamic sampling used for this statement

Statistics

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

         0  recursive calls

         0  db block gets

         4  consistent gets

         0  physical reads

         0  redo size

       483  bytes sent via SQL*Net to client

       400  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

         0  sorts (memory)

         0  sorts (disk)

         1  rows processed

SQL> set autotrace trace stat   －－显示物理统计信息

SQL> select * from t where rownum=1;

Statistics

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

         0  recursive calls

         0  db block gets

         4  consistent gets

         0  physical reads

         0  redo size

       483  bytes sent via SQL*Net to client

       400  bytes received via SQL*Net from client

         2  SQL*Net roundtrips to/from client

         0  sorts (memory)

         0  sorts (disk)

         1  rows processed

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

总结：

set autotrace on                ＝ set autotrace on     exp stat

set autotrace on     exp stat

             on     exp

             on     stat

             trace             ＝ trace  exp stat

             trace  exp stat

             trace  exp

             trace  stat

只要有on，一定会显示数据，只要有trace，就不显示数据。

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

2、dbms_xplan  --通过内部的包，仅仅显示执行计划

解释执行计划

SQL> explain plan for select * from t where rownum=1;

Explained.

查看执行计划

SQL> select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT

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

Plan hash value: 508354683

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

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

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

|   0 | SELECT STATEMENT   |      |     1 |    28 |     2   (0)| 00:00:01 |

|*  1 |  COUNT STOPKEY     |      |       |       |            |          |

|   2 |   TABLE ACCESS FULL| T    | 43751 |  1196K|     2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

PLAN_TABLE_OUTPUT

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

  1 - filter(ROWNUM=1)

Note

-----

  - dynamic sampling used for this statement

18 rows selected.