使用dbms_xplan查看执行计划

概述

dbms_xplan包提供了多样的，预定义的方式去解释执行计划。sql执行计划，执行时间等信息都存储与v$sql_plan,v$sql_plan_statistics_all视图中。此包运行的权限是执行用户，不是包的拥有者sys。

当执行diplay_awr时，需要DBA_HIST_SQL_PLAN, DBA_HIST_SQLTEXT, and V$DATABASE的查询权限

当执行display_cursor时需要V$SQL_PLAN, V$SESSION and V$SQL_PLAN_STATISTICS_ALL的查询权限

当执行display_sql_plan_baseline时，需要DBA_SQL_PLAN_BASELINES的查询权限

当执行display_sqlset时，需要ALL_SQLSET_STATEMENTS and ALL_SQLSET_PLANS的查询权限

以上的所有权限都在SELECT_CATALOG角色中，所以直接赋权SELECT_CATALOG就可以了。

dbms_xplan中有许多功能，我这里着重研究其中几个常用的

SQL> desc dbms_xplan;

…

FUNCTION DISPLAY_AWR RETURNS DBMS_XPLAN_TYPE_TABLE

 Argument Name Type In/Out Default?

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

 SQL_ID VARCHAR2 IN

 PLAN_HASH_VALUE NUMBER(38) IN     DEFAULT

 DB_ID NUMBER(38) IN     DEFAULT

 FORMAT VARCHAR2 IN     DEFAULT

FUNCTION DISPLAY_CURSOR RETURNS DBMS_XPLAN_TYPE_TABLE

 Argument Name Type In/Out Default?

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

 SQL_ID VARCHAR2 IN     DEFAULT

 CURSOR_CHILD_NO NUMBER(38) IN     DEFAULT

 FORMAT VARCHAR2 IN     DEFAULT

FUNCTION DISPLAY_PLAN RETURNS CLOB

 Argument Name Type In/Out Default?

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

 TABLE_NAME VARCHAR2 IN     DEFAULT

 STATEMENT_ID VARCHAR2 IN     DEFAULT

 FORMAT VARCHAR2 IN     DEFAULT

 FILTER_PREDS VARCHAR2 IN     DEFAULT

 TYPE VARCHAR2 IN     DEFAULT

FUNCTION DISPLAY_SQLSET RETURNS DBMS_XPLAN_TYPE_TABLE

 Argument Name Type In/Out Default?

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

 SQLSET_NAME VARCHAR2 IN

 SQL_ID VARCHAR2 IN

 PLAN_HASH_VALUE NUMBER(38) IN     DEFAULT

 FORMAT VARCHAR2 IN     DEFAULT

 SQLSET_OWNER VARCHAR2 IN     DEFAULT

FUNCTION DISPLAY_SQL_PLAN_BASELINE RETURNS DBMS_XPLAN_TYPE_TABLE

 Argument Name Type In/Out Default?

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

 SQL_HANDLE VARCHAR2 IN     DEFAULT

 PLAN_NAME VARCHAR2 IN     DEFAULT

 FORMAT VARCHAR2 IN     DEFAULT

…

dbms_xplan.display

展示执行计划内容

简单的执行一次display

SQL> explain plan for insert into scott.emp values(1111,'xplan','','','','','','');

Explained.

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

7 rows selected.

Execution Plan

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

Plan hash value: 2137789089

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

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

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

|   0 | SELECT STATEMENT   |     |  8168 | 16336 | 29   (0)| 00:00:01 |

|   1 |  COLLECTION ITERATOR PICKLER FETCH| DISPLAY |  8168 | 16336 | 29   (0)| 00:00:01 |

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

Statistics

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

       1890  recursive calls

40  db block gets

       3635  consistent gets

  0  physical reads

  0  redo size

       1102  bytes sent via SQL*Net to client

523  bytes received via SQL*Net from client

  2  SQL*Net roundtrips to/from client

38  sorts (memory)

  0  sorts (disk)

  7  rows processed

SQL> select * from scott.emp where empno=1111;

no rows selected

—explain plan for ，dbms_xplan.display都没有执行sql。explain plan for是产生sql的执行计划并保存在PLAN_TABLE表中，dbms_xplan.display从PLAN_TABLE中提取计划并展示出来。

定义

DBMS_XPLAN.DISPLAY(

   table_name    IN  VARCHAR2  DEFAULT 'PLAN_TABLE',

   statement_id  IN  VARCHAR2  DEFAULT  NULL, 

   format            IN  VARCHAR2  DEFAULT  'TYPICAL',

   filter_preds     IN  VARCHAR2 DEFAULT NULL);

table_name：指定的是计划的存储表表名（不是执行表的表名）。默认是PLAN_TABLE。

statement_id：指定计划的statement_id，如果没有指定，则该值为explain plan的statement_id , 如果没有expain plan，则该值为最近一次解释的执行计划。

format：解释计划的level

? BASIC: Displays the minimum information in the plan—the operation ID, the operation name and its option.展示最少的信息

? TYPICAL: This is the default. Displays the most relevant information in the plan (operation id, name and option, #rows, #bytes and optimizer cost). Pruning, parallel and predicate information are only displayed when applicable. Excludes only PROJECTION, ALIAS and REMOTE SQL information (see below).默认值

? SERIAL: Like TYPICAL except that the parallel information is not displayed, even if the plan executes in parallel.没有并发信息

? ALL: Maximum user level. Includes information displayed with the TYPICAL level with additional information (PROJECTION, ALIAS and information about REMOTE SQL if the operation is distributed).展示最多的信息，包含了分布式操作的远程sql执行信息

filter_preds：sql过滤，限制从计划表中返回的行。

dbms_xplan.display_awr  

展示在awr中存储的sql的执行计划

定义

DBMS_XPLAN.DISPLAY_AWR( 

   sql_id            IN      VARCHAR2,

   plan_hash_value   IN      NUMBER DEFAULT NULL,

   db_id             IN      NUMBER DEFAULT NULL,

   format            IN      VARCHAR2 DEFAULT TYPICAL);

sql_id:在dba_hist_sqltext中可以找到sql_id

plan_hash_value:sql执行计划的hash值。如果该值被忽略，则函数返回sql_id中的所有执行计划

db_id：database_id。如果不知道则该值为V$DATABASE视图中的database_id，也就是本地数据库。

format：与display类似。总共有4个level：BASIC，TYPICAL,SERIAL,ALL。

SQL> select * from scott.emp where rownum<=1;

     EMPNO ENAME      JOB       MGR HIREDATE     SAL       COMM

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

    DEPTNO

----------

      7369 SMITH      CLERK       7902 17-DEC-80     800

20

—手动生成快照

SQL> EXECUTE DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT();

PL/SQL procedure successfully completed.

SQL> select sql_id,sql_text from dba_hist_sqltext where sql_text like '%rownum%';

SQL_ID

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

SQL_TEXT

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

6yzbcy3x0yr1j

insert into wrh$_dispatcher   (snap_id, dbid, instance_number,   name, serial#,

fsbqktj5vw6n9

select next_run_date, obj#, run_job, sch_job from (select decode(bitand(a.flags,

cv959u044n88s

select 1 from sys.aq$_subscriber_table where rownum < 2 and subscriber_id <> 0 a

…

SQL_ID

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

SQL_TEXT

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

bd3tcy3ar02px

select * from scott.emp where rownum<=1

7 rows selected.

SQL> 

—指定awr中存在sql

SQL> select * from table(dbms_xplan.display_awr('bd3tcy3ar02px'));

PLAN_TABLE_OUTPUT

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

SQL_ID bd3tcy3ar02px

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

select * from scott.emp where rownum<=1

Plan hash value: 1973284518

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

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

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

|   0 | SELECT STATEMENT   |   |   |   | 2 (100)|   |

|   1 |  COUNT STOPKEY   |   |   |   |       |   |

PLAN_TABLE_OUTPUT

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

|   2 |   TABLE ACCESS FULL| EMP  |    15 |  1305 | 2   (0)| 00:00:01 |

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

Note

-----

   - dynamic sampling used for this statement (level=2)

18 rows selected.

SQL> 

dbms_xplan.display_cursor

展示cursor中的执行计划

定义

DBMS_XPLAN.DISPLAY_CURSOR(

   sql_id           IN  VARCHAR2  DEFAULT  NULL,

   cursor_child_no  IN  NUMBER    DEFAULT  0, 

   format           IN  VARCHAR2  DEFAULT  ‘TYPICAL');

sql_id

cursor_child_no:子游标标志。如果没有指定，则展示sql_id下的所有执行计划

format

默认值执行

SQL> select * from scott.emp where rownum<=2;

     EMPNO ENAME      JOB       MGR HIREDATE     SAL       COMM

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

    DEPTNO

----------

      7369 SMITH      CLERK       7902 17-DEC-80     800

20

      7499 ALLEN      SALESMAN       7698 20-FEB-81   1600        300

30

—默认查询了当前session最后一次执行sql

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

PLAN_TABLE_OUTPUT

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

SQL_ID 90ud69jbjz75c, child number 0

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

select * from scott.emp where rownum<=2

Plan hash value: 1973284518

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

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

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

|   0 | SELECT STATEMENT   |   |   |   | 2 (100)|   |

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

PLAN_TABLE_OUTPUT

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

|   2 |   TABLE ACCESS FULL| EMP  |    15 |  1305 | 2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   1 - filter(ROWNUM<=2)

Note

-----

   - dynamic sampling used for this statement (level=2)

PLAN_TABLE_OUTPUT

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

23 rows selected.

SQL> 

指定sql_id查找plan，首先要找到sql_id

SQL> select sql_id,sql_text from v$sqlarea where sql_text like '%rownum<=2%';

SQL_ID

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

SQL_TEXT

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

75gpskbx0uk8w

select sql_id,sql_text from v$sqlarea where sql_text like '%rownum<=2%'

90ud69jbjz75c

select * from scott.emp where rownum<=2

SQL> select * from table(dbms_xplan.display_cursor('90ud69jbjz75c'));

PLAN_TABLE_OUTPUT

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

SQL_ID 90ud69jbjz75c, child number 0

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

select * from scott.emp where rownum<=2

Plan hash value: 1973284518

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

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

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

|   0 | SELECT STATEMENT   |   |   |   | 2 (100)|   |

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

PLAN_TABLE_OUTPUT

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

|   2 |   TABLE ACCESS FULL| EMP  |    15 |  1305 | 2   (0)| 00:00:01 |

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

Predicate Information (identified by operation id):

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

   1 - filter(ROWNUM<=2)

Note

-----

   - dynamic sampling used for this statement (level=2)

PLAN_TABLE_OUTPUT

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

23 rows selected.

SQL> 

如果sql不在内存中，则不能通过cursor方式查询

SQL> select * from table(dbms_xplan.display_cursor('90ud69jbjz75c'));

PLAN_TABLE_OUTPUT

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

SQL_ID: 90ud69jbjz75c, child number: 0 cannot be found

这时就可以通过生成快照的方式从awr中查询plan

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