Resolving High CPU Usage on Oracle Servers(读书笔记)

最新推荐文章于 2024-06-25 10:16:23 发布

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最新推荐文章于 2024-06-25 10:16:23 发布

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文章标签： oracle loops nested object access table

本文链接：https://blog.youkuaiyun.com/Lijun_blue/article/details/7067046

本文分析了一篇关于在安装应用安全补丁后出现性能问题的Oracle邮件应用案例，通过top-down方法，从收集服务器CPU使用率、top和vmstat数据开始，进一步收集SQL跟踪数据和构建问题查询的测试脚本。通过分析问题SQL执行计划，定位到性能瓶颈，并最终通过优化查询和重建索引来解决问题。

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今天读了oracle的Case Study中的一篇文章：Resolving High CPU Usage on Oracle Servers.

案例讲述了一个email application中在安装了一些application secucurity patches之后出现的性能问题。服务器是一个2-cpu的Linux Server。
对案例的分析主要采用top-down的方法，大体流程是这样的：

出问题时的top数据如下：
# of processes in the run queue             CPU User mode 
           CPU Sys mode 
            CPU idle 
 
zzz ***Thu Mar 9 18:30:00 PST 2006 
          cpu  procs                      memory    swap          io     system    
 r  b  w   swpd   free   buff  cache  si  so    bi    bo   in    cs  us  sy  id 
 3  0  0    920   8596 342908 4088164   0   0    10   514  501  1790  43   7  50 
 5  0  0    920   8844 343024 4089564   0   0     8    79  319  1751  29   4  67 
21  0  1    920   5332 343160 4093964   0   0    18   320  390  1690  97   3   0 
22  0  0    920  22864 343304 4057500   0   0    11   149  370  2563  97   3   0 
25  0  3    920   9728 343404 4059732   0   0    77   412  400  2412  95   5   0 
23  0  0    920   8416 343688 4044128   0   0     2     2  254  1308  97   3   0 
21  0  1    920   6760 343520 4045256   0   0    56  2428  704  2382  89  10   1 
24  0  0    920  14856 343812 4045968   0   0    54    66  278  2785  95   5   0 
21  0  2    920  17600 343956 4048296   0   0    17    70  249  1677  96   4   0 
20  0  0    920   6028 344080 4050368   0   0     8    52  265  1461  94   6   0 
22  0  1    920  27172 344184 4053608   0   0    25    49  263  2513  96   4   0 
14  0  2    920  58264 344364 4057036   0   0    73   125  614  3821  79  20   1 
 1  1  0    920  65756 344476 4070080   0   0   358  1964  410  2118  12   4  84 
 0  0  0    920  48628 344580 4080864   0   0    17   106  229  1190   9   2  88

对案例的分析主要采用top-down的方法，大体流程是这样的：

1. Verify CPU consumption on the server,collect top and vmstat data for a period of time.
2. collect extended sql trace data(event 10046)
   gather sid,serial#,and other information from v$session about these sessions;
   trace the sessions using an extendes sql trace via event 10046,level 12;
   produce a TKPROF report and look for the queries having the longest elasped time
3. build a best case script for the problem query(使用绑定变量值）
4. obtain statspack snapshots,collect statspack snapshots during the same time period as the OS were collected and look for correlations
   with the session-level data collected in step 2.
5. tune the query

设置10046事件
SQL> SELECT p.spid, s.sid, s.serial#  
FROM v$session s, v$process p 
WHERE s.paddr = p.addr AND p.spid = 24078 
 
 
SPID                SID    SERIAL# 
------------ ---------- ---------- 
24078                18          5 
 
SQL> begin dbms_system.set_ev(18,5, 10046,12,''); end; -- trace on 
 
-- collect trace information for approximately 15 minutes during the problem 
 
SQL> begin dbms_system.set_ev(18, 5, 10046,0,''); end; -- trace off

问题SQL的执行计划
Rows     Row Source Operation 
-------  --------------------------------------------------- 
     19  TABLE ACCESS BY INDEX ROWID DS_ATTRSTORE  
     26   NESTED LOOPS  
      1    NESTED LOOPS  
      1     VIEW VW_NSO_1  
      1      SORT UNIQUE  
      1       UNION-ALL  
      0        TABLE ACCESS BY INDEX ROWID CT_OBJECTCLASS  
      0         INDEX RANGE SCAN (object id 55349) 
      1        TABLE ACCESS BY INDEX ROWID CT_OBJECTCLASS  
  64439         NESTED LOOPS  
      2          TABLE ACCESS BY INDEX ROWID CT_MAIL  
      2           INDEX RANGE SCAN (object id 55355) 
  64436          INDEX RANGE SCAN (object id 55349) 
CBO used VA_OBJECTCLASS 
index due to INDEX hint 
      0        TABLE ACCESS BY INDEX ROWID CT_OBJECTCLASS  
     27         NESTED LOOPS  
      2          TABLE ACCESS BY INDEX ROWID CT_MAIL  
      2           INDEX RANGE SCAN (object id 55355) 
     24          INDEX RANGE SCAN (object id 55349) 
      1     TABLE ACCESS BY INDEX ROWID CT_DN  
      1      INDEX RANGE SCAN (object id 55345) 
     24    INDEX RANGE SCAN (object id 55340) 
 
定位问题的原因后，重新创建索引后，执行计划
call     count       cpu    elapsed       disk      query    current        rows 
------- ------  -------- ---------- ---------- ---------- ----------  ---------- 
Parse        1      0.02       0.01          0          0          0           0 
Execute      1      0.00       0.00          0          0          0           0 
Fetch        4      0.00       0.00          0         63          0          43 
------- ------  -------- ---------- ---------- ---------- ----------  ---------- 
total        6      0.02       0.01          0         63          0          43 
 
Misses in library cache during parse: 1 
Optimizer goal: CHOOSE 
Parsing user id: 141   
 
Rows     Row Source Operation 
-------  --------------------------------------------------- 
     43  TABLE ACCESS BY INDEX ROWID DS_ATTRSTORE  
     45   NESTED LOOPS  
      1    NESTED LOOPS  
      1     VIEW VW_NSO_1  
      1      SORT UNIQUE  
      1       UNION-ALL  
CBO chose a different index 
(ST_OBJECTCLASS) 
      0        TABLE ACCESS BY INDEX ROWID CT_OBJECTCLASS  
      0         INDEX RANGE SCAN (object id 55349) 
      1        NESTED LOOPS  
      2         TABLE ACCESS BY INDEX ROWID CT_MAIL  
      2          INDEX RANGE SCAN (object id 55355) 
      1         INDEX RANGE SCAN (object id 55348) 
      0        NESTED LOOPS  
      2         TABLE ACCESS BY INDEX ROWID CT_MAIL  
      2          INDEX RANGE SCAN (object id 55355) 
      0         INDEX RANGE SCAN (object id 55348) 
      1     TABLE ACCESS BY INDEX ROWID CT_DN  
      1      INDEX RANGE SCAN (object id 55345) 
     43    INDEX RANGE SCAN (object id 55340) 
 
Elapsed times include waiting on following events: 
  Event waited on                             Times   Max. Wait  Total Waited 
  ----------------------------------------   Waited  ----------  ------------ 
  SQL*Net message to client                       4        0.00          0.00 
  SQL*Net message from client                     4        1.25          1.29

问题得到解决。

文章名字为CS_HighCPU.pdf。