Oracle查看sql执行计划的方式
获取Oracle sql执行计划并查看执行计划，是掌握和判断数据库性能的基本技巧。下面案例介绍了多种查看sql执行计划的方式：
基本有以下几种方式：
1、通过sql_trace初始化参数
2、通过Autotrace
3、通过explain plan
4、通过dbms_xplan.display_cursor
5、通过dbms_xplan.display_awr
6、通过10046事件
1、通过explain plan 工具
12:24:00 SCOTT@ prod>explain plan for
12:24:06 2 select empno,ename,sal,deptno from emp where empno=7788;
Explained.
Elapsed: 00:00:00.22
12:24:16 SCOTT@ prod>select * from table(dbms_xplan.display);
PLAN_TABLE_OUTPUT
------------------------------------------------------------------------------------------------------
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%cpu)| Time |
| 0 | SELECT STATEMENT | | 1 | 46 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 46 | 2 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=7788)
14 rows selected.
Elapsed: 00:00:01.14
2、通过DBMS_XPLAN.display_cursor查看
12:52:37 SCOTT@ prod>desc dbms_xplan
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
如果以scott用户访问需要进行授权：
12:31:44 SYS@ prod>select * from dict where upper(table_name)='V$SESSION';
TABLE_NAME COMMENTS
------------------------------ ----------------------------------------
V$SESSION Synonym for V_$SESSION
Elapsed: 00:00:00.09
12:31:09 SYS@ prod>grant select on V_$SESSION to scott;
Grant succeeded.
Elapsed: 00:00:00.10
12:43:15 SCOTT@ prod>select * from table(dbms_xplan.display_cursor(null,null,'advanced'));
User has no SELECT privilege on V$sql_PLAN
解决权限不足：
12:42:33 SYS@ prod>grant select any table to scott;
12:43:46 SYS@ prod>show parameter o7
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
O7_DICTIONARY_ACCESSIBILITY boolean TRUE
12:44:54 SYS@ prod>
案例：dbms_xplan.display_cursor
12:42:45 SCOTT@ prod>select empno,serif; font-size:14px"> EMPNO ENAME SAL DEPTNO
---------- ---------- ---------- ----------
7788 SCOTT 3000 20
Elapsed: 00:00:00.08
12:43:15 SCOTT@ prod>select * from table(dbms_xplan.display_cursor(null,'all'));
sql_ID bqz9ujgnn4jzu,child number 0
-------------------------------------
select empno,deptno from emp where empno=7788
| 0 |SELECT STATEMENT | | | | 2 (100)| |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 46 | 2 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 1 (0)| 00:00:01 |
Query Block Name / Object Alias (identified by operation id):
-------------------------------------------------------------
1 - SEL$1 / EMP@SEL$1
2 - SEL$1 / EMP@SEL$1
Column Projection Information (identified by operation id):
-----------------------------------------------------------
1 - "EMPNO"[NUMBER,22],"ENAME"[VARCHAR2,10],"SAL"[NUMBER,
"DEPTNO"[NUMBER,22]
2 - "EMP".ROWID[ROWID,"EMPNO"[NUMBER,serif; font-size:14px"> 32 rows selected.
Elapsed: 00:00:00.05
案例：
12:49:10 SCOTT@ prod>select empno,serif; font-size:14px"> Elapsed: 00:00:00.00
12:50:06 SCOTT@ prod>select * from table(dbms_xplan.display_cursor(null,serif; font-size:14px"> | 0 | SELECT STATEMENT | | | | 2 (100)| |
Outline Data
-------------
/*+
BEGIN_OUTLINE_DATA
IGNORE_OPTIM_EMBEDDED_HINTS
OPTIMIZER_FEATURES_ENABLE('11.2.0.1')
DB_VERSION('11.2.0.1')
ALL_ROWS
OUTLINE_LEAF(@"SEL$1")
INDEX_RS_ASC(@"SEL$1" "EMP"@"SEL$1" ("EMP"."EMPNO"))
END_OUTLINE_DATA
*/
46 rows selected.
Elapsed: 00:00:00.06
12:50:21 SCOTT@ prod>
这种方法在 sqlPLUS中查看刚执行过的 sqlsqlsql的执行计划 。
-- dbms_xplan.display_cursor传入的前两个参数值均为 null,null第三个参数是 "advanced"第三个参 数也可以是 "all"得到的显示结果，少了 "Outline data"部分的内容 。
sql>select sql_text,sql_id,hash_value,child_number from v$sql
2* where sql_text like 'select empno,sal%'
sql_TEXT sql_ID HASH_VALUE CHILD_NUMBER
-------------------------------------------------- ------------- ---------- ------------
bqz9ujgnn4jzu 3913435130 0
=7788
Elapsed: 00:00:00.04
13:00:25 SCOTT@ prod>select * from table(dbms_xplan.display_cursor('bqz9ujgnn4jzu',serif; font-size:14px"> Elapsed: 00:00:00.14
3、通过DBMS_XPLAN.display_awr
使用方法dbms_xplan.display_cursor能够得到sql执行计划的前提条件是该sql还在共享池中，而如果执行计划的前提条件是该sql还在共享池中，而如果执行计划的前提条件是该 还在共享池中，而如果sqlsqlsql的执行计划已经被刷出共享池，那么只要该sql的执行计划被ORACLE采集到 AWR Repository中， 就可以用该方法来查看 。
12:24:00 SCOTT@ prod>select empno,deptno from emp where empno=7788;
13:10:56 SYS@ prod>exec dbms_workload_repository.create_snapshot;
PL/sql procedure successfully completed.
13:11:37 SYS@ prod>alter system flush shared_pool;
System altered.
Elapsed: 00:00:00.31
13:16:28 SYS@ prod>select * from table(dbms_xplan.display_cursor('bqz9ujgnn4jzu',0)">sql_ID: bqz9ujgnn4jzu,child number: 0 cannot be found
13:21:53 SYS@ prod>desc dbms_xplan
FUNCTION DISPLAY_AWR RETURNS DBMS_XPLAN_TYPE_TABLE
sql_ID VARCHAR2 IN
PLAN_HASH_VALUE NUMBER(38) IN DEFAULT
DB_ID NUMBER(38) IN DEFAULT
13:30:15 SCOTT@ prod>select * from table(dbms_xplan.display_awr('bqz9ujgnn4jzu'));
sql_ID bqz9ujgnn4jzu
--------------------
select empno,serif; font-size:14px"> | 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 1 (0)| 00:00:01 |
Elapsed: 00:00:00.30
4、通过10046 事件查看
1）查看当前session：
13:29:52 SYS@ prod>grant alter session to scott;
13:44:31 SCOTT@ prod>alter session set events '10046 trace name context forever,level 12';
Session altered.
13:44:53 SCOTT@ prod>select empno,serif; font-size:14px"> 13:45:51 SCOTT@ prod>alter session set events '10046 trace name context off';
Elapsed: 00:00:00.03
[oracle@rh6 ~]$ ls -lt /u01/app/oracle/diag/rdbms/prod/prod/trace/|more
total 1256
-rw-r----- 1 oracle oinstall 27801 May 16 13:46 prod_ora_4995.trc
-rw-r----- 1 oracle oinstall 177 May 16 13:46 prod_ora_4995.trm
-rw-r----- 1 oracle oinstall 1122 May 16 13:34 prod_j000_5188.trc
-rw-r----- 1 oracle oinstall 59 May 16 13:34 prod_j000_5188.trm
......
[oracle@rh6 ~]$ tkprof /u01/app/oracle/diag/rdbms/prod/prod/trace/prod_ora_4995.trc /home/oracle/emp_0416.txt sys=no
TKPROF: Release 11.2.0.1.0 - Development on Fri May 16 13:47:41 2014
Copyright (c) 1982,2009,Oracle and/or its affiliates. All rights reserved.
[oracle@rh6 ~]$ cat emp_0416.txt
sql ID: bqz9ujgnn4jzu
Plan Hash: 2949544139
from
emp where empno=7788
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.07 0.09 1 66 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 2 0 1
total 4 0.07 0.09 1 68 0 1
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 84
Rows Row Source Operation
------- ---------------------------------------------------
1 TABLE ACCESS BY INDEX ROWID EMP (cr=2 pr=0 pw=0 time=0 us cost=2 size=46 card=1)
1 INDEX UNIQUE SCAN PK_EMP (cr=1 pr=0 pw=0 time=0 us cost=1 size=0 card=1)(object id 73202)
Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
db file sequential read 1 0.00 0.00
sql*Net message to client 2 0.00 0.00
sql*Net message from client 2 19.13 19.13
********************************************************************************
2）查看其它session：
14:12:23 SYS@ prod>select sid,serial#,username from v$session where username is not null;
SID SERIAL# USERNAME
---------- ---------- ------------------------------
1 5 SYS
42 9SCOTT
6 rows selected.
14:12:47 SYS@ prod>desc dbms_monitor
PROCEDURE SESSION_TRACE_DISABLE
SESSION_ID BINARY_INTEGER IN DEFAULT
SERIAL_NUM BINARY_INTEGER IN DEFAULT
PROCEDURE SESSION_TRACE_ENABLE
WAITS BOOLEAN IN DEFAULT
BINDS BOOLEAN IN DEFAULT
PLAN_STAT VARCHAR2 IN DEFAULT
14:13:11 SCOTT@ prod>select sid from v$mystat where rownum=1;
SID
----------
42
14:13:41 SYS@ prod>exec dbms_monitor.SESSION_TRACE_ENABLE(42,9,waits=>true,binds=>true);
14:13:25 SCOTT@ prod>select empno,deptno from emp where empno=7369;
7369 SMITH 800 20
14:14:29 SYS@ prod>exec dbms_monitor.SESSION_TRACE_disable(42,9);
Elapsed: 00:00:00.02
sql ID: fyydvbdw2uq6q
emp where empno=7369
Parse 1 0.00 0.00 0 0 0 0
total 4 0.00 0.00 0 2 0 1
------- ---------------------------------------------------
1 TABLE ACCESS BY INDEX ROWID EMP (cr=2 pr=0 pw=0 time=0 us cost=2 size=46 card=1)
1 INDEX UNIQUE SCAN PK_EMP (cr=1 pr=0 pw=0 time=0 us cost=1 size=0 card=1)(object id 73202)
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 1 0.00 0.00
5、通过autotrace查看
SET AUTOTRACE ON
SET AUTOTRACE TRACEONLY
SET AUTOTRACE TRACEONLY EXPLAIN
--使用SET AUTOTRACE ON和SET AUTOTRACE TRACEONLY时，目标sql已经被执行过，所以在SET AUTOTRACE ON和SET AUTOTRACE TRACEONLY 的情况下能看到目标sql
的实际消耗情况。
--使用SET AUTOTRACE TRACEONLY EXPLAIN时，如果执行的是SELECT语句，则该sql并没有被执行，但如果执行的是DML语句，情况就不一样了，此时的DML语句是会
被ORACLE执行的。
--需要特别说明的是，虽然使用SET AUTOTRACE命令所得到的执行计划可能是不准确的，因为SET AUTOTRACE命令所显示的执行计划都是源自于explain plan 命令。
案例：
15:32:11 SYS@ prod>conn scott/tiger
Connected.
15:32:17 SCOTT@ prod>set autotrace on
15:32:21 SCOTT@ prod>select empno,simsun"> EMPNO ENAME SAL DEPTNO
---------- ---------- ---------- ----------
7788 SCOTT 3000 20
Elapsed: 00:00:00.03
Execution Plan
----------------------------------------------------------
Plan hash value: 2949544139
--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%cpu)| Time |
| 0 | SELECT STATEMENT | | 1 | 46 | 2 (0)| 00:00:01 |
| 1 | TABLE ACCESS BY INDEX ROWID| EMP | 1 | 46 | 2 (0)| 00:00:01 |
|* 2 | INDEX UNIQUE SCAN | PK_EMP | 1 | | 1 (0)| 00:00:01 |
Predicate Information (identified by operation id):
---------------------------------------------------
2 - access("EMPNO"=7788)
Statistics
168 recursive calls
0 db block gets
38 consistent gets
0 physical reads
0 redo size
736 bytes sent via sql*Net to client
523 bytes received via sql*Net from client
2 sql*Net roundtrips to/from client
5 sorts (memory)
0 sorts (disk)
1 rows processed
15:32:26 SCOTT@ prod>set autotrace trace
15:32:49 SCOTT@ prod>select empno,simsun">Elapsed: 00:00:00.02
0 recursive calls
2 consistent gets
0 sorts (memory)
15:34:59 SCOTT@ prod>set autotrace on exp
15:35:04 SCOTT@ prod>select empno,simsun">15:35:12 SCOTT@ prod>set autotrace on statis
15:35:20 SCOTT@ prod>select empno,simsun">15:35:26 SCOTT@ prod>
@至此，Oracle下查看sql执行计划的几种方式介绍完毕，大家可根据自己的爱好来使用！
