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Oracle诊断案例-Sql_trace之一

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

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 successfully 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.

By eygle on 2004-06-26 23:43 | Comments (1) | Case | 33 |

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