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 ptimizer=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 ptimizer=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>
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