查看oracle执行计划方法（ 一）

关于oracle执行计划的概念，参考之前的博客：http://blog.csdn.net/cymm_liu/article/details/7996599

如果要分析某条SQL的性能问题，通常我们要先看SQL的执行计划，看看SQL的每一步执行是否存在问题。 如果一条SQL平时执行的好好的，却有一天突然性能很差，如果排除了系统资源和阻塞的原因，那么基本可以断定是执行计划出了问题。

看懂执行计划也就成了SQL优化的先决条件。 这里的SQL优化指的是SQL性能问题的定位，定位后就可以解决问题。

一．         查看执行计划的5种方法

1.1 设置autotrace

序号	命令	解释
1	SET AUTOTRACE OFF	此为默认值，即关闭Autotrace
2	SET AUTOTRACE ON EXPLAIN	只显示执行计划
3	SET AUTOTRACE ON STATISTICS	只显示执行的统计信息
4	SET AUTOTRACE ON	包含2,3两项内容
5	SET AUTOTRACE TRACEONLY	与ON相似，但不显示语句的执行结果

 

SQL> set autotrace on

SQL> SET AUTOTRACE TRACEONLY;
SQL> select empno,ename,dname from scott.emp,scott.dept where emp.deptno=dept.deptno;

14 rows selected.

Execution Plan
----------------------------------------------------------
Plan hash value: 844388907
--------------------------------------------------------------------------------
| Id  | Operation     | Name    | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------

|   0 | SELECT STATEMENT     |      |    14 |   364 |     6 (17)| 00:00:01 |

|   1 |  MERGE JOIN     |      |    14 |   364 |     6 (17)| 00:00:01 |

|   2 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     4 |    52 |     2(0)| 00:00:01 |

|   3 |    INDEX FULL SCAN     | PK_DEPT |     4 |       |     1(0)| 00:00:01 |

|*  4 |   SORT JOIN     |      |    14 |   182 |     4 (25)| 00:00:01 |

|   5 |    TABLE ACCESS FULL     | EMP     |    14 |   182 |     3(0)| 00:00:01 |

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

Predicate Information (identified by operation id):
---------------------------------------------------

   4 - access("EMP"."DEPTNO"="DEPT"."DEPTNO")
       filter("EMP"."DEPTNO"="DEPT"."DEPTNO")

Statistics
----------------------------------------------------------
 0  recursive calls
 0  db block gets
10  consistent gets
 0  physical reads
 0  redo size
941  bytes sent via SQL*Net to client
523  bytes received via SQL*Net from client
 2  SQL*Net roundtrips to/from client
 1  sorts (memory)
 0  sorts (disk)
14  rows processed

1.2 使用SQL

SQL>EXPLAIN PLAN FOR sql语句;

SQL>SELECT plan_table_output FROM TABLE(DBMS_XPLAN.DISPLAY('PLAN_TABLE'));

 

示例：

SQL> EXPLAIN PLAN FOR SELECT * FROM dual;

已解释。

SQL> SELECT plan_table_output FROM TABLE(DBMS_XPLAN.DISPLAY('PLAN_TABLE'));

或者：

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

1.3 oradebug

SQL> oradebug setmypid;
Statement processed.
SQL> oradebug event 10046 trace name context forever,level 12;         
——打开10046
Statement processed.
SQL> select empno,ename,dname from scott.emp,scott.dept where emp.deptno=dept.deptno; 
        ——执行想看计划的语句

     EMPNO ENAME      DNAME
---------- ---------- --------------
      7782 CLARK      ACCOUNTING
      7839 KING       ACCOUNTING
      7934 MILLER     ACCOUNTING
      7566 JONES      RESEARCH
      7902 FORD       RESEARCH
      7876 ADAMS      RESEARCH
      7369 SMITH      RESEARCH
      7788 SCOTT      RESEARCH
      7521 WARD       SALES
      7844 TURNER     SALES
      7499 ALLEN      SALES

     EMPNO ENAME      DNAME
---------- ---------- --------------
      7900 JAMES      SALES
      7698 BLAKE      SALES
      7654 MARTIN     SALES

14 rows selected.

SQL> oradebug tracefile_name;         
——查看跟踪文件名字
/u01/app/oracle/diag/rdbms/test/test/trace/test_ora_17425.trc
SQL> oradebug event 10046 trace name context off;        ——关闭跟踪事件
Statement processed. 

现在，根据查询出的跟踪文件名字，去查看执行计划：

需要对trace文件进行格式化，方便我们查看，使用tkprof：

[oracle@lyg ~]$ tkprof  /u01/app/oracle/diag/rdbms/test/test/trace/test_ora_17425.trc output= ./exptest/test_ora_17425.trc

TKPROF: Release 11.2.0.3.0 - Development on Wed Mar 26 11:27:52 2014

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

[oracle@lyg ~]$ cd exptest/
[oracle@lyg exptest]$ ls
compressfile  expfull.log  exptest.sh  pxe.sh  test.dmp.gz test_ora_17425.trc
[oracle@lyg exptest]$ vi test_ora_17425.trc   （附上全部内容）

TKPROF: Release 11.2.0.3.0 - Development on Wed Mar 26 11:27:52 2014

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

Trace file: /u01/app/oracle/diag/rdbms/test/test/trace/test_ora_17425.trc

Sort options: default

********************************************************************************
count    = number of times OCI procedure was executed

cpu      = cpu time in seconds executing 

elapsed  = elapsed time in seconds executing

disk     = number of physical reads of buffers from disk

query    = number of buffers gotten for consistent read

current  = number of buffers gotten in current mode (usually for update)

rows     = number of rows processed by the fetch or execute call

********************************************************************************

SQL ID: 3yfu3wh150aqt Plan Hash: 844388907

select empno,ename,dname 

from

 scott.emp,scott.dept where emp.deptno=dept.deptno

call     count       cpu    elapsed       disk      query    current        rows

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

Parse        1      0.00       0.01          0          0          0           0

Execute      1      0.00       0.00          0          0          0           0

Fetch        2      0.00       0.00          0         10          0          14

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

total        4      0.01       0.01          0         10          0          14

Misses in library cache during parse: 1

Optimizer mode: ALL_ROWS

Parsing user id: SYS

Number of plan statistics captured: 1

Rows (1st) Rows (avg) Rows (max)  Row Source Operation

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

        14         14         14  MERGE JOIN  (cr=10 pr=0 pw=0 time=520 us cost=6 size=364 card=14)

         4          4          4   TABLE ACCESS BY INDEX ROWID DEPT (cr=4 pr=0 pw=0 time=329 us cost=2 size=52 card=4)

         4          4          4    INDEX FULL SCAN PK_DEPT (cr=2 pr=0 pw=0 time=173 us cost=1 size=0 card=4)(object id 75334)

        14         14         14   SORT JOIN (cr=6 pr=0 pw=0 time=242 us cost=4 size=182 card=14)

        14         14         14    TABLE ACCESS FULL EMP (cr=6 pr=0 pw=0 time=170 us cost=3 size=182 card=14)

Elapsed times include waiting on following events:

  Event waited on                             Times   Max. Wait  Total Waited

  ----------------------------------------   Waited  ----------  ------------

  SQL*Net message to client                       2        0.00          0.00

  SQL*Net message from client                     2       11.50         11.50

********************************************************************************

OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS

call     count       cpu    elapsed       disk      query    current        rows

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

Parse        1      0.00       0.01          0          0          0           0

Execute      1      0.00       0.00          0          0          0           0

Fetch        2      0.00       0.00          0         10          0          14

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

total        4      0.01       0.01          0         10          0          14

Misses in library cache during parse: 1

Elapsed times include waiting on following events:

  Event waited on                             Times   Max. Wait  Total Waited

  ----------------------------------------   Waited  ----------  ------------

  SQL*Net message to client                       4        0.00          0.00

  SQL*Net message from client                     4       12.79         33.45

OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS

call     count       cpu    elapsed       disk      query    current        rows

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

Parse        0      0.00       0.00          0          0          0           0

Execute      0      0.00       0.00          0          0          0           0

Fetch        0      0.00       0.00          0          0          0           0

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

total        0      0.00       0.00          0          0          0           0

Misses in library cache during parse: 0

    1  user  SQL statements in session.

    0  internal SQL statements in session.

    1  SQL statements in session.

********************************************************************************

Trace file: /u01/app/oracle/diag/rdbms/test/test/trace/test_ora_17425.trc

Trace file compatibility: 11.1.0.7

Sort options: default

       1  session in tracefile.

       1  user  SQL statements in trace file.

       0  internal SQL statements in trace file.

       1  SQL statements in trace file.

       1  unique SQL statements in trace file.

      86  lines in trace file.

       0  elapsed seconds in trace file.

1.4 通过hash_value,child_number查看执行过的sql语句的执行计划

SQL> col sql_text format a30;
SQL> select sql_text,sql_id,hash_value,child_number from v$sql where sql_text like '%select empno,ename,dname from scott.emp,scott.dept where emp.deptno=dept.deptno%';

SQL_TEXT                                   SQL_ID 
  HASH_VALUE    CHILD_NUMBER
------------------------------                        -------------            ----------            ------------
select empno,ename,dname from  088zzpvnu02r4 3919579876 
0
scott.emp,scott.dept where emp
.deptno=dept.deptno

select empno,ename,dname from  3yfu3wh150aqt   38808281  0
scott.emp,scott.dept where emp
.deptno=dept.deptno

select empno,ename,dname from  3yfu3wh150aqt   38808281  1
scott.emp,scott.dept where emp
.deptno=dept.deptno

3 rows selected.

SQL> select * from table(dbms_xplan.display_cursor(3919579876,0,'advanced'));

PLAN_TABLE_OUTPUT

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

HASH_VALUE  3919579876, child number 0

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

select empno,ename,dname from scott.emp,scott.dept where

emp.deptno=dept.deptno

Plan hash value: 844388907

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

--------

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

PLAN_TABLE_OUTPUT

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

|   0 | SELECT STATEMENT     |      |       |       |     6 (100)|       |

|   1 |  MERGE JOIN     |      |    14 |   364 |     6
(17)| 00:00:01 |

PLAN_TABLE_OUTPUT

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

|   2 |   TABLE ACCESS BY INDEX ROWID| DEPT    |     4 |    52 |     2(0)| 00:00:01 |

|   3 |    INDEX FULL SCAN     | PK_DEPT |     4 |       |     1(0)| 00:00:01 |

|*  4 |   SORT JOIN     |      |    14 |   182 |     4
(25)| 00:00:01 |

|   5 |    TABLE ACCESS FULL     | EMP     |    14 |   182 |     3(0)| 00:00:01 |

PLAN_TABLE_OUTPUT

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

Query Block Name / Object Alias (identified by operation id):

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

   1 - SEL$1

   2 - SEL$1 / DEPT@SEL$1

   3 - SEL$1 / DEPT@SEL$1

PLAN_TABLE_OUTPUT

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

   5 - SEL$1 / EMP@SEL$1

Outline Data

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

  /*+

      BEGIN_OUTLINE_DATA

      IGNORE_OPTIM_EMBEDDED_HINTS

      OPTIMIZER_FEATURES_ENABLE('11.2.0.3')

      DB_VERSION('11.2.0.3')

      ALL_ROWS

PLAN_TABLE_OUTPUT

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

      OUTLINE_LEAF(@"SEL$1")

      INDEX(@"SEL$1" "DEPT"@"SEL$1" ("DEPT"."DEPTNO"))

      FULL(@"SEL$1" "EMP"@"SEL$1")

      LEADING(@"SEL$1" "DEPT"@"SEL$1" "EMP"@"SEL$1")

      USE_MERGE(@"SEL$1" "EMP"@"SEL$1")

      END_OUTLINE_DATA

  */

Predicate Information (identified by operation id):

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

PLAN_TABLE_OUTPUT

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

   4 - access("EMP"."DEPTNO"="DEPT"."DEPTNO")

       filter("EMP"."DEPTNO"="DEPT"."DEPTNO")

Column Projection Information (identified by operation id):

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

   1 - "DNAME"[VARCHAR2,14], "EMPNO"[NUMBER,22], "ENAME"[VARCHAR2,10]

   2 - "DEPT"."DEPTNO"[NUMBER,22], "DNAME"[VARCHAR2,14]

   3 - "DEPT".ROWID[ROWID,10], "DEPT"."DEPTNO"[NUMBER,22]

   4 - (#keys=1) "EMP"."DEPTNO"[NUMBER,22], "EMPNO"[NUMBER,22],

       "ENAME"[VARCHAR2,10]

PLAN_TABLE_OUTPUT

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

   5 - "EMPNO"[NUMBER,22], "ENAME"[VARCHAR2,10], "EMP"."DEPTNO"[NUMBER,22]

59 rows selected.

SQL> 

1.5 使用Toad,PL/SQL Developer工具



 
图片是Toad工具查看的执行计划。 在Toad 里面，很清楚的显示了执行的顺序。 但是如果在SQLPLUS里面就不是那么直接。 但我们也可以判断：一般按缩进长度来判断，缩进最大的最先执行，如果有2行缩进一样，那么就先执行上面的。