Oracle诊断案例-Sql_trace之一_数据库

Oracle诊断案例-Sql_trace之一

发表于：2007-06-08来源：作者：点击数：标签：

link: sql_trace_1.htm">http://www.eygle.com/case/sql_trace_1.htm 问题描述: 这是帮助一个公司的诊断案例. 应用是一个后台新闻发布系统. 症状是,通过连接访问新闻页是极其缓慢通常需要十数秒才能返回. 这种性能是用户不能忍受的. 操作系统:SunOS 5.8

link:

sql_trace_1.htm">http://www.eygle.com/case/sql_trace_1.htm

问题描述:

这是帮助一个公司的诊断案例.
应用是一个后台新闻发布系统.

症状是,通过连接访问新闻页是极其缓慢
通常需要十数秒才能返回.

这种性能是用户不能忍受的.

操作系统:SunOS 5.8
数据库版本:8.1.7

1.检查并跟踪数据库进程

诊断时是晚上,无用户访问
在前台点击相关页面,同时进行进程跟踪

查询v$session视图,获取进程信息

SQL> select sid,serial#,username from v$session;



       SID    SERIAL# USERNAME

---------- ---------- ------------------------------

         1          1

         2          1

         3          1

         4          1

         5          1

         6          1

         7        284 IFLOW

        11        214 IFLOW

        12        164 SYS

        16       1042 IFLOW



10 rows selected.

启用相关进程sql_trace



SQL> exec dbms_system.set_sql_trace_in_session(7,284,true)



PL/SQL procedure suclearcase/" target="_blank" >ccessfully completed.



SQL> exec dbms_system.set_sql_trace_in_session(11,214,true)



PL/SQL procedure successfully completed.



SQL> exec dbms_system.set_sql_trace_in_session(16,1042,true)



PL/SQL procedure successfully completed.



SQL> select sid,serial#,username from v$session;



       SID    SERIAL# USERNAME

---------- ---------- ------------------------------

         1          1

         2          1

         3          1

         4          1

         5          1

         6          1

         7        284 IFLOW

        11        214 IFLOW

        12        164 SYS

        16       1042 IFLOW



10 rows selected.

等候一段时间,关闭sql_trace

SQL> exec dbms_system.set_sql_trace_in_session(7,284,false)



PL/SQL procedure successfully completed.



SQL> exec dbms_system.set_sql_trace_in_session(11,214,false)



PL/SQL procedure successfully completed.





SQL> exec dbms_system.set_sql_trace_in_session(16,1042,false)



PL/SQL procedure successfully completed.

2.检查trace文件

检查发现以下语句是可疑的



********************************************************************************



select auditstatus,categoryid,auditlevel 

from

 categoryarticleassign a,category b where b.id=a.categoryid and articleId=

  20030700400141 and auditstatus>0





call     count       cpu    elapsed       disk      query    current        rows

------- ------  -------- ---------- ---------- ---------- ----------  ----------

Parse        1      0.00       0.00          0          0          0           0

Execute    1      0.00       0.00          0          0          0           0

Fetch        1      0.81       0.81          0       3892          0           1

------- ------  -------- ---------- ---------- ---------- ----------  ----------

total        3      0.81       0.81          0        3892           0         1

********************************************************************************

这里显然是根据articleId进行新闻读取的.
很可疑的是query读取有3892

这个内容引起了我的注意.
如果遇到过类似的问题，大家在这里就应该知道是怎么回事情了.
如果没有遇到过的朋友，可以在这里思考一下再往下看.


Misses in library cache during parse: 1

Optimizer goal: CHOOSE

Parsing user id: 41  



Rows     Row Source Operation

-------  ---------------------------------------------------

      1  NESTED LOOPS 

      2   INDEX RANGE SCAN (object id 25062)

      1   TABLE ACCESS BY INDEX ROWID CATEGORY 

      2    INDEX UNIQUE SCAN (object id 25057)



********************************************************************************



select auditstatus,categoryid 

from

 categoryarticleassign where articleId=20030700400138 and categoryId in ('63',

  '138','139','140','141','142','143','144','168','213','292','341','346',

  '347','348','349','350','351','352','353','354','355','356','357','358',

  '359','360','361','362','363','364','365','366','367','368','369','370',

  '371','372','383','460','461','462','463','621','622','626','629','631',

  '634','636','643','802','837','838','849','850','851','852','853','854',

  '858','859','860','861','862','863','-1')





call     count       cpu    elapsed       disk      query    current        rows

------- ------  -------- ---------- ---------- ---------- ----------  ----------

Parse        1      0.00       0.00          0          0          0           0

Execute      1      0.00       0.00          0          0          0           0

Fetch        1      4.91       4.91          0       2835          7           1

------- ------  -------- ---------- ---------- ---------- ----------  ----------

total        3      4.91       4.91          0       2835          7           1



Misses in library cache during parse: 1

Optimizer goal: CHOOSE

Parsing user id: 41  



Rows     Row Source Operation

-------  ---------------------------------------------------

      1 'TABLE ACCESS FULL CATEGORYARTICLEASSIGN'



我们注意到，这里有一个全表扫描存在





********************************************************************************

3.登陆数据库,检查相应表结构




SQL> select index_name,table_name,column_name from user_ind_columns

  2  where table_name=upper('categoryarticleassign');



INDEX_NAME                     TABLE_NAME                     COLUMN_NAME                    

------------------------------ ------------------------------ --------------------           

IDX_ARTICLEID                              CATEGORYARTICLEASSIGN          ARTICLEID

IND_ARTICLEID_CATEG                  CATEGORYARTICLEASSIGN          ARTICLEID                     

IND_ARTICLEID_CATEG                  CATEGORYARTICLEASSIGN          CATEGORYID                    

IDX_SORTID                                   CATEGORYARTICLEASSIGN          SORTID                        

PK_CATEGORYARTICLEASSIGN       CATEGORYARTICLEASSIGN          ARTICLEID                     

PK_CATEGORYARTICLEASSIGN       CATEGORYARTICLEASSIGN          CATEGORYID                    

PK_CATEGORYARTICLEASSIGN       CATEGORYARTICLEASSIGN          ASSIGNTYPE                    

IDX_CAT_ARTICLE                          CATEGORYARTICLEASSIGN          AUDITSTATUS                   

IDX_CAT_ARTICLE                          CATEGORYARTICLEASSIGN          ARTICLEID                     

IDX_CAT_ARTICLE                          CATEGORYARTICLEASSIGN          CATEGORYID                    

IDX_CAT_ARTICLE                          CATEGORYARTICLEASSIGN          ASSIGNTYPE                    



11 rows selected.

我们注意到,IDX_ARTICLEID索引在以上查询中都没有被用到.

检查表结构:

SQL> desc categoryarticleassign

 Name                                      Null?    Type

 ----------------------------------------- -------- ----------------------------

 CATEGORYID                                NOT NULL NUMBER

 ARTICLEID                                 NOT NULL VARCHAR2(14)

 ASSIGNTYPE                                NOT NULL VARCHAR2(1)

 AUDITSTATUS                               NOT NULL NUMBER

 SORTID                                    NOT NULL NUMBER

 UNPASS                                             VARCHAR2(255)

问题发现:
因为ARTICLEID是个字符型数据,查询中给入的articleId= 20030700400141 是一个数字值
Oracle发生潜在的数据类型转换,从而导致了索引失效

SQL>  select auditstatus,categoryid

  2   from

  3    categoryarticleassign where articleId=20030700400132;



AUDITSTATUS CATEGORYID                                     

----------- ----------                                     

          9         94                                     

          0        383                                     

          0        695                                     



Elapsed: 00:00:02.62



Execution Plan

----------------------------------------------------------                 

   0      SELECT STATEMENT Optimizer=CHOOSE (Cost=110 Card=2 Bytes=38)    

   1    0   TABLE ACCESS (FULL) OF 'CATEGORYARTICLEASSIGN' (Cost=110 Card=2 Bytes=38)

4.解决方法

简单的在参数两侧各增加一个',既可解决这个问题.

对于类似的查询,我们发现Query模式读取降低为2
几乎不需要花费CPU时间了

 

********************************************************************************



select unpass 

from

 categoryarticleassign where articleid='20030320000682' and categoryid='113' 



call     count       cpu    elapsed       disk      query    current        rows

------- ------  -------- ---------- ---------- ---------- ----------  ----------

Parse        1      0.00       0.00          0          0          0           0

Execute    1      0.00       0.00          0          0          0           0

Fetch        1      0.00       0.00          0          2          0           0

------- ------  -------- ---------- ---------- ---------- ----------  ----------

total        3      0.00       0.00          0          2          0           0



Misses in library cache during parse: 1

Optimizer goal: CHOOSE

Parsing user id: 20  



Rows     Row Source Operation

-------  ---------------------------------------------------

      0  TABLE ACCESS BY INDEX ROWID CATEGORYARTICLEASSIGN 

      1   INDEX RANGE SCAN (object id 3080)



********************************************************************************

至此,这个问题得到了完满的解决.

原文转自：http://www.ltesting.net

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