在SQL*Plus中，你可以通过设置autotrace选项来在执行SQL命令的同时，自动的获得语句的执行计划和附加的统计信息。AUTOTRACE是一个很出色的Oracle SQL语句的诊断工具，与Explain plan不同的是这条SQL是实际执行了的，同时AUTOTRACE使用起来也极为方便。


一、启用Autotrace功能。
任何以SQL*PLUS连接的session都可以用Autotrace,不过还是要做一些设置的，否则可能报错。

1、报错示例：
SQL :> set autotrace on;
SP2-0613: Unable to verify PLAN_TABLE format or existence
SP2-0611: Error enabling EXPLAIN report
SP2-0618: Cannot find the Session Identifier. Check PLUSTRACE role is enabled
SP2-0611: Error enabling STATISTICS report

2、解决方法：

a.以SYS用户运行plustrce.sql脚本

cd $ORACLE_HOME/sqlplus/admin

oracle>sqlplus \'/ as sysdba\';
SQL>@plustrce.sql

b.给任何想使用Autotrace的用户授PLUSTRACE权限。

SQL>grant plustrace to hr;

c.同时被授权的用户比如hr用户的PLAN_TABLE这个表必须存在。如果不存在这样：

cd $ORACLE_HOME/sqlplus/admin

oracle>sqlplus hr/hr; --hr为示例用户
SQL>@utlxplan.sql

二、设置Autotrace的命令。

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。

三、Autotrace执行计划的各列的涵义

序号 列名   解释
1 ID_PLUS_EXP 每一步骤的行号
2 PARENT_ID_PLUS_EXP 每一步的Parent的级别号
3 PLAN_PLUS_EXP 实际的每步
4 OBJECT_NODE_PLUS_EXP   Dblink或并行查询时才会用到

四、AUTOTRACE Statistics常用列解释

序号 统计列 解释
1 db block gets 从buffer cache中读取的block的数量
2 consistent gets 从buffer cache中读取的undo数据的block的数量
3 physical reads 从磁盘读取的block的数量
4 redo size DML生成的redo的大小
5 sorts (memory) 在内存执行的排序量
7 sorts (disk) 在磁盘上执行的排序量

五、示例

oracle@yang:~> sqlplus hr/hr

SQL*Plus: Release 9.2.0.4.0 - Production on Wed Apr 12 15:46:56 2006

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning, Oracle Label Security, OLAP and Oracle Data Mining options
JServer Release 9.2.0.4.0 - Production

SQL>set autotrace on;

SQL> select b.DEPARTMENT_NAME,sum(a.SALARY)
2 from employees a,departments b
3 where a.DEPARTMENT_ID=b.DEPARTMENT_ID
4 group by b.DEPARTMENT_NAME
5 /

DEPARTMENT_NAME SUM(A.SALARY)
------------------------------ -------------
Accounting 20300
Administration 4400
Executive 58000
Finance 51600
Human Resources 6500
IT 28800
Marketing 19000
Public Relations 10000
Purchasing 24900
Sales 304500
Shipping 156400

11 rows selected.

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

SQL> set autotrace on
SQL> /

DEPARTMENT_NAME SUM(A.SALARY)
------------------------------ -------------
Accounting 20300
Administration 4400
Executive 58000
Finance 51600
Human Resources 6500
IT 28800
Marketing 19000
Public Relations 10000
Purchasing 24900
Sales 304500
Shipping 156400

11 rows selected.

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=25 Card=27 Bytes=621
)

1 0 SORT (GROUP BY) (Cost=25 Card=27 Bytes=621)
2 1 HASH JOIN (Cost=21 Card=106 Bytes=2438)
3 2 TABLE ACCESS (FULL) OF \'DEPARTMENTS\' (Cost=10 Card=27
Bytes=432)

4 2 TABLE ACCESS (FULL) OF \'EMPLOYEES\' (Cost=10 Card=107 B
ytes=749)



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

SQL> edit
Wrote file afiedt.buf

1 select b.DEPARTMENT_NAME,sum(a.SALARY)
2 from employees a,departments b
3 where a.DEPARTMENT_ID=b.DEPARTMENT_ID
4* group by b.DEPARTMENT_NAME
SQL> /

DEPARTMENT_NAME SUM(A.SALARY)
------------------------------ -------------
Accounting 20300
Administration 4400
Executive 58000
Finance 51600
Human Resources 6500
IT 28800
Marketing 19000
Public Relations 10000
Purchasing 24900
Sales 304500
Shipping 156400

11 rows selected.

Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=25 Card=27 Bytes=621
)

1 0 SORT (GROUP BY) (Cost=25 Card=27 Bytes=621)
2 1 HASH JOIN (Cost=21 Card=106 Bytes=2438)
3 2 TABLE ACCESS (FULL) OF \'DEPARTMENTS\' (Cost=10 Card=27
Bytes=432)

4 2 TABLE ACCESS (FULL) OF \'EMPLOYEES\' (Cost=10 Card=107 B
ytes=749)



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

SQL>