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;
SIDSERIAL# USERNAME
---------- ---------- ------------------------------
11
21
31
41
51
61
7284 IFLOW
11214 IFLOW
12164 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;
SIDSERIAL# USERNAME
---------- ---------- ------------------------------
11
21
31
41
51
61
7284 IFLOW
11214 IFLOW
12164 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 auditstatus0
call count cpuelapsed diskquerycurrentrows
------- -------------- ---------- ---------- ---------- --------------------
Parse10.00 0.00000 0
Execute10.00 0.00000 0
Fetch10.81 0.810 38920 1
------- -------------- ---------- ---------- ---------- --------------------
total30.81 0.810 '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
----------------------------------------------------------
1NESTED LOOPS
2 INDEX RANGE SCAN (object id 25062)
1 TABLE Access BY INDEX ROWID CATEGORY
2INDEX 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 cpuelapsed diskquerycurrentrows
------- -------------- ---------- ---------- ---------- --------------------
Parse10.00 0.00000 0
Execute10.00 0.00000 0
Fetch14.91 4.910 28357 1
------- -------------- ---------- ---------- ---------- --------------------
total34.91 4.910 28357 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
2where table_name=upper('categoryarticleassign');
INDEX_NAME TABLE_NAME COLUMN_NAME
------------------------------ ------------------------------ --------------------
'IDX_ARTICLEIDCATEGORYARTICLEASSIGNARTICLEID'
IND_ARTICLEID_CATEGCATEGORYARTICLEASSIGNARTICLEID
IND_ARTICLEID_CATEGCATEGORYARTICLEASSIGNCATEGORYID
IDX_SORTID CATEGORYARTICLEASSIGNSORTID
PK_CATEGORYARTICLEASSIGN CATEGORYARTICLEASSIGNARTICLEID
PK_CATEGORYARTICLEASSIGN CATEGORYARTICLEASSIGNCATEGORYID
PK_CATEGORYARTICLEASSIGN CATEGORYARTICLEASSIGNASSIGNTYPE
IDX_CAT_ARTICLECATEGORYARTICLEASSIGNAUDITSTATUS
IDX_CAT_ARTICLECATEGORYARTICLEASSIGNARTICLEID
IDX_CAT_ARTICLECATEGORYARTICLEASSIGNCATEGORYID
IDX_CAT_ARTICLECATEGORYARTICLEASSIGNASSIGNTYPE
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
NameNull?
Type
----------------------------------------- -------- ----------------------------
CATEGORYI