在Oracle10g Release 2中的Autotrace
2024-08-29 13:42:37
供稿：網(wǎng)友
今天在測試過程中，偶然發(fā)現(xiàn)在Oracle10g Release 2中，Autotrace的功能已經(jīng)被極大加強和改變。
這是一個很有意思的小的變化，關(guān)于autotrace的使用，請參考:啟用AutoTrace
接下來讓我們先來看一下什么地方發(fā)生了改變: 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
注重，此時autotrace的輸出被良好格式化，并給出關(guān)于執(zhí)行計劃部分的簡要注釋。
其實這里并沒有帶來新的東西，從Oracle9i開始，Oracle提供了一個新的工具dbms_XPlan用以格式化和查看SQL的執(zhí)行計劃。其原理是通過對plan_table的查詢和格式化提供更友好的用戶輸出。
dbms_xplan的調(diào)用的語法類似:
select * from table(dbms_xplan.display(format=>'BASIC'))
使用 TABLE() 操作符，或者 CAST 操作。
具體用法可以參考Oracle官方文檔。
實際上從Oracle9i開始我們就經(jīng)常使用如下方式調(diào)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腳本中正是調(diào)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幫我們簡化了這個過程，一個autotrace就完成了所有的輸出，這也是易用性上的一個進步吧。在使用 Oracle的過程中，我們經(jīng)常能夠感受到Oracle針對用戶需求或易用性的改進，這也許是很多人喜愛Oracle的一個原因吧。
假如足夠信息我們還會注重到，在Oracle10g中PLAN_TABLE不再需要創(chuàng)建，Oracle缺省增加了一個字典表PLAN_TABLE$，然后基于PLAN_TABLE$創(chuàng)建公用同義詞供用戶使用。
關(guān)于dbms_xplan工具的使用還可以參考Itpub上的討論:使用dbms_xplan工具查看執(zhí)行計劃.
