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$session视图,获取进程信息
代码:
SQL> select sid,serial#,username from v$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
代码:
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
代码:
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
代码:
********************************************************************************
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 &nb
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重.
假如碰到过类似的问题，大家在这里就应该知道是怎么回事情了.假如没有碰到过的朋友，可以在这里思考一下再往下看.
代码:
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'
我们注重到，这里有一个全表扫描存在
********************************************************************************
3.登陆数据库,检查相应表结构
代码:
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.
我们注重到,IDX_ARTICLEID索引在以上查询中都没有被用到.
检查表结构:
代码:
SQL> desc categoryarticleassign
Name Null?
Type
----------------------------------------- -------- ----------------------------
CATEGORYI
|
