今天在测试过程中，偶然发现在Oracle10g Release 2中，Autotrace的功能已经被极大加强和改变。
这是一个很有意思的小的变化，关于autotrace的使用，请参考:启用AutoTrace
接下来让我们先来看一下什么地方发生了改变: SQL set linesize 120
SQL set autotrace on
SQL select count(*) from v$session
2
/
COUNT(*)
----------
21
Execution Plan
----------------------------------------------------------
Plan hash value: 2376410614
---------------------------------------------------------------------------------------------
| Id
| Operation
| Name
| Rows
| Bytes | Cost (%CPU)| Time
|
---------------------------------------------------------------------------------------------
|
0 | SELECT STATEMENT
|
|
1 |
65 |
0
(0)| 00:00:01 |
|
1 |
SORT AGGREGATE
|
|
1 |
65 |
|
|
|
2 |
NESTED LOOPS
|
|
1 |
65 |
0
(0)| 00:00:01 |
|*
3 |
FIXED TABLE FULL
| X$KSUSE
|
1 |
52 |
0
(0)| 00:00:01 |
|*
4 |
FIXED TABLE FIXED INDEX| X$KSLED (ind:2) |
1 |
13 |
0
(0)| 00:00:01 |
---------------------------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
3 - filter("S"."INST_ID"=USERENV('INSTANCE') AND BITAND("S"."KSSPAFLG",1)<0 AND
BITAND("S"."KSUSEFLG",1)<0)
4 - filter("S"."KSUSEOPC"="E"."INDX")
Statistics
----------------------------------------------------------
1
recursive calls
0
db block gets
0
consistent gets
0
physical reads
0
redo size
411
bytes sent via SQL*Net to client
385
bytes received via SQL*Net from client
2
SQL*Net roundtrips to/from client
0
sorts (memory)
0
sorts (disk)
1
rows processed
注意，此时autotrace的输出被良好格式化，并给出关于执行计划部分的简要注释。
其实这里并没有带来新的东西，从Oracle9i开始，Oracle提供了一个新的工具dbms_xplan用以格式化和查看SQL的执行计划。其原理是通过对plan_table的查询和格式化提供更友好的用户输出。
dbms_xplan的调用的语法类似:
select * from table(dbms_xplan.display(format='BASIC'))
使用 TABLE() 操作符，或者 CAST 操作。
具体用法可以参考Oracle官方文档。
实际上从Oracle9i开始我们就经常使用如下方式调用dbms_xplan:
Connected to:
Oracle9i Enterprise Edition Release 9.2.0.4.0 - Production
With the Partitioning option
JServer Release 9.2.0.4.0 - Production
SQL explain plan for
2
select count(*) from dual;
Explained.
SQL @?/rdbms/admin/utlxplp;
PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------
--------------------------------------------------------------------
| Id
| Operation
|
Name
| Rows
| Bytes | Cost
|
--------------------------------------------------------------------
|
0 | SELECT STATEMENT
|
|
|
|
|
|
1 |
SORT AGGREGATE
|
|
|
|
|
|
2 |
TABLE ACCESS FULL
| DUAL
|
|
|
|
--------------------------------------------------------------------
Note: rule based optimization
10 rows selected.
utlxplp.sql脚本中正是调用了dbms_xplan:
SQL get ?/rdbms/admin/utlxplp;
1
Rem
2
Rem $Header: utlxplp.sql 23-jan-2002.08:55:23 bdagevil Exp $
3
Rem
4
Rem utlxplp.sql
5
Rem
6
Rem Copyright (c) 1998, 2002, Oracle Corporation.
All rights reserved.
7
Rem
8
Rem
NAME
9
Rem
utlxplp.sql - UTiLity eXPLain Parallel plans
10
Rem
11
Rem
DESCRIPTION
12
Rem
script utility to display the explain plan of the last explain plan
13
Rem
command. Display also Parallel Query information if the plan happens to
14
Rem
run parallel
15
Rem
16
Rem
NOTES
17
Rem
Assume that the table PLAN_TABLE has been created. The script
18
Rem
utlxplan.sql should be used to create that table
19
Rem
20
Rem
With SQL*plus, it is recomended to set linesize and pagesize before
21
Rem
running this script. For example:
22
Rem
set linesize 130
23
Rem
set pagesize 0
24
Rem
25
Rem
MODIFIED
(MM/DD/YY)
26
Rem
bdagevil
01/23/02 - rewrite with new dbms_xplan package
27
Rem
bdagevil
04/05/01 - include CPU cost
28
Rem
bdagevil
02/27/01 - increase Name column
29
Rem
jihuang
06/14/00 - change order by to order siblings by.
30
Rem
jihuang
05/10/00 - include plan info for recursive SQL in LE row source
31
Rem
bdagevil
01/05/00 - make deterministic with order-by
32
Rem
bdagevil
05/07/98 - Explain plan script for parallel plans
33
Rem
bdagevil
05/07/98 - Created
34
Rem
35
set markup html preformat on
36
Rem
37
Rem Use the display table function from the dbms_xplan package to display the last
38
Rem explain plan. Use default mode which will display only relevant information
39
Rem
40* select * from table(dbms_xplan.display());
41
SQL
而在Oracle10gR2中，Oracle帮我们简化了这个过程，一个autotrace就完成了所有的输出，这也是易用性上的一个进步吧。在使用Oracle的过程中，我们经常能够感受到Oracle针对用户需求或易用性的改进，这也许是很多人喜爱Oracle的一个原因吧。
如果足够信息我们还会注意到，在Oracle10g中PLAN_TABLE不再需要创建，Oracle缺省增加了一个字典表PLAN_TABLE$，然后基于PLAN_TABLE$创建公用同义词供用户使用。
关于dbms_xplan工具的使用还可以参考Itpub上的讨论:使用dbms_xplan工具查看执行计划.
