link:

http://www.eygle.com/case/sga2.htm

案例描述:

这是一个大型生产系统
问题出现时系统累计大量用户进程
用户请求得不到及时呼应，新的进程不断尝试建立连接
连接数很快被用完

数据库版本:9.2.0.3
操作系统:Solaris8

 

1.检查alert文件

日志中记录如下错误信息，说明磁盘异步IO出现问题:



 

WARNING: aiowait timed out 2 times
Tue Aug 26 15:33:32 2003
WARNING: aiowait timed out 2 times
Tue Aug 26 15:33:34 2003
WARNING: aiowait timed out 2 times
Tue Aug 26 15:33:36 2003
WARNING: aiowait timed out 2 times
Tue Aug 26 15:33:38 2003
WARNING: aiowait timed out 2 times
Tue Aug 26 15:33:43 2003
WARNING: aiowait timed out 1 times
Tue Aug 26 15:33:46 2003
WARNING: aiowait timed out 1 times
Tue Aug 26 15:33:49 2003
WARNING: aiowait timed out 1 times
Tue Aug 26 15:33:51 2003
WARNING: aiowait timed out 1 times
Tue Aug 26 15:33:52 2003
WARNING: aiowait timed out 1 times
Tue Aug 26 15:33:53 2003
WARNING: aiowait timed out 1 times
.............


我们知道在SUN的某些版本上异步IO存在问题
而异步IO缺省是打开的



 

SQL> show parameter disk_a

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
disk_asynch_io boolean TRUE

 

针对此问题，我们停用了数据库的异步IO写入。

2.共享内存问题

alert文件中还记录了以下错误信息:


 

Tue Aug 26 21:37:40 2003
WARNING: EINVAL creating segment of size 0x0000000190400000
fix shm parameters in /etc/system or equivalent

 



该信息说明内核参数设置过小或者和SGA不婚配

我们检查system配置文件



 

$ cat /etc/system
.......................
set shmsys:shminfo_shmmax=4096000000
set shmsys:shminfo_shmmin=1
set shmsys:shminfo_shmmni=200
set shmsys:shminfo_shmseg=200
set semsys:seminfo_semmap=1024
set semsys:seminfo_semmni=2048
set semsys:seminfo_semmns=2048
set semsys:seminfo_semmnu=2048
set semsys:seminfo_semume=200
set semsys:seminfo_semmsl=2048

 



我们发现最大共享内存设置仅有4G

 

3.检查SGA设置

 


SQL*Plus: Release 9.2.0.3.0 - Production on 星期二 8月 26 21:46:35 2003

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.


Connected to:
Oracle9i Enterprise Edition Release 9.2.0.3.0 - 64bit Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.3.0 - Production

SQL> show sga

Total System Global Area 6695660272 bytes
Fixed Size 740080 bytes
Variable Size 2399141888 bytes
Database Buffers 4294967296 bytes
Redo Buffers 811008 bytes

 




我们发现SGA设置接近7G，这也就是步骤2中错误提示出现的缘由


4.交换区问题

我们用top工具检查系统运转情况



 

# /usr/local/bin/top

last pid: 16899; load averages: 0.82, 0.81, 0.83 21:49:05
1230 processes:1228 sleeping, 1 running, 1 on cpu
CPU states: 50.1% idle, 7.4% user, 8.6% kernel, 33.9% iowait, 0.0% swap
Memory: 8192M real, 118M free, 12G swap in use, 11G swap free

PID USERNAME THR PRI NICE SIZE RES STATE TIME CPU COMMAND
15751 oracle 11 44 0 6456M 6408M sleep 0:02 0.49% oracle
15725 oracle 11 58 0 6458M 6410M sleep 0:02 0.46% oracle
251 root 12 48 0 7096K 1944K sleep 126:00 0.45% picld
16540 oracle 11 58 0 6458M 6411M sleep 0:01 0.45% oracle
16766 root 1 43 0 3744K 2248K cpu/1 0:01 0.41% top
16408 oracle 11 58 0 6457M 6410M sleep 0:01 0.34% oracle
15989 oracle 11 58 0 6458M 6409M sleep 0:01 0.34% oracle
15919 oracle 11 58 0 6457M 6409M sleep 0:02 0.30% oracle
16404 oracle 11 58 0 6457M 6409M sleep 0:00 0.28% oracle
16327 oracle 11 55 0 6457M 6410M sleep 0:00 0.27% oracle
14870 oracle 11 58 0 6457M 6412M sleep 0:05 0.24% oracle
16851 oracle 11 35 0 6457M 641