DBCA Fails With ORA-15243

今天接到朋友的电话说他们装ORACLE 11G R1 RAC的时候遇到ORA-12801/ORA-15243错误,请求我帮忙解决
具体情况
AIX系统以前装过11G R2 RAC,现因为项目要求11G R1,已经重装了系统,然后安装R1,在安装到DBCA配置ASM的时候,出现ORA-12801/ORA-15243错误

ORA-12801: error signaled in parallel query server PZ99, instance wmsdb1:+ASM1(1)
ORA-15243: 11.2.0.0.0 is not a valid version number


通过SQLPLUS登录ASM1实例查询发现该有一个ORADATA磁盘组,包含了一个/dev/rhdisk1.通过询问,得出结论是这个磁盘组以前是安装R2的时候作为存储OCR和VOTINGDISK使用,重装系统的时候未对该磁盘进行处理.

处理思路[想办法清除磁盘中asm信息]
1.尝试通过sqlplus 删除该磁盘组,报该磁盘组处于dismount状态
2.尝试mount该磁盘组,提示版本无效(ORA-15243)[当前的asm程序是11.1而磁盘组信息是11.2 程序当然不一致了]
3.直接使用dd清理该asm disk header信息(dd if=/dev/zero of=/dev/rhdisk1 bs=4096 count=1)
4.重新运行dbca一切工作正常

MOS中相关文章[1460997.1]只适合linux asmlib情况

Applies to:
Oracle Server - Enterprise Edition - Version 11.1.0.7 and later
Information in this document applies to any platform.

Symptoms
On : 11.1.0.7 version, STORAGE

When attempting to create database or query gv$asm_diskgroup,
the following error occurs.

ERROR
-----------------------
ORA-12801: error signaled in parallel query server PZ99, instance dchilcmsdb2.hq.navteq.com:+ASM2 (2)
ORA-15243: 11.2.0.0.0 is not a valid version number


STEPS
-----------------------
The issue can be reproduced at will with the following steps:
1. Previously had 11GR2 installed and configured. Removed this installation then installed 
   11.1.0.7  and created diskgroups using some of the same disks previously used.
2. Attempt to create database and receive the errors. Drop the newly 
   created diskgroups and query the view still get same errors.


BUSINESS IMPACT
-----------------------
The issue has the following business impact:
Due to this issue, users cannot create new database.

Changes
 Removed 11.2.0.1 installation and installed 11.1.0.7 software without cleaning up all of 
 the diskgroup information from previous installation.

Cause
All the current information shows that we are using correct binaries and 
that the diskgroups that are being used have correct comparability settings. 
HTML shows that the disks for the old diskgroup are still being discovered. 
This in conjunction with the text of the error as follows shows that 
we are picking up 11.2.0.0.0 as version from somewhere.
ORA-15243: 11.2.0.0.0 is not a valid version number
 
Problem was caused by the disks that had been used for the 
OCR/Voting disk diskgroup in 11GR2 installation still being present and accessible.
 

Solution
As the root user execute /etc/init.d/oracleasm/deletedisk command against all the disks 
that were previously used for the OCR/Voting disk diskgroup then try the operation again.

11g DirectPath Reads 噩梦案例

DirectPath Reads 说明
在oracle 11g以前的版本中,如果对大表进行全表扫描,wait event是:db file scattered read;在11g中,如果对大表进行全表扫描,wait event是:direct path read。在11g中,大表全表扫描时数据块不经过sga而直接进pga,这样会造成每次进行大表全表扫描,物理读都是很大,而在10g中,由于全表扫描的数据块在sga中已经存在,所以执行全表扫描时,它的物理读为0。但是这里主要是oracle在优化策略上的进步,即假定大表频繁全表扫描这种现象,在生产库上不会太多,通过把数据直接读入pga,进而减少了cache buffer的繁忙交换程度,提高了cache buffer的使用效率.

DirectPath Reads 优势
1. 减少了对栓的使用,避免可能的栓争用
2. 物理IO的大小不再取决于buffer_cache中所存在的块;试想某个8个块的extent中1,3,5,7号块在高速缓存中,而2,4,6,8块没有被缓存,传统的方式在读取该extent时将会是对2,4,6,8块进行4次db file sequential read,这是一种十分可怕的状况,其效率往往要比单次读取这个区间的所有8个块还要低得多,虽然Oracle为了避免这种情况总是尽可能的不缓存大表的块(读入后总是放在队列最冷的一端);而direct path read则可以完全避免这类问题,尽可能地单次读入更多的物理块。

DirectPath Reads 噩梦
这一切听起来都很美好,但是在大并发的OLTP系统中,这东西简直是一个噩梦.通过一个awr来说明该问题:这个是一个系统的awr报告,朋友反馈说系统有段运行缓慢,请求帮忙找出原因
分析总体信息

系统这段时间会话临时大幅度增加(从102增加到223),系统出现异常繁忙(60.62*16=969.92<2,454.52)
分析Load Profile信息

通过这个截图发现系统的业务不是很大,但是Physical reads参数异常
1.物理读大小:25071.1*8192/1024/1024=195.86796875M/S
2.物理读将近逻辑读一半,这个在一般系统中很难得到这个比例,进一步说明物理读过高

分析Top 5信息

这里可以发现direct path read等待很多

分析Host CPU

可以发现iowait很大占40.5%,io等待异常高(195M/S能不高吗?)
补充说明:在这里我们看到的%Idle=1-%System-%User不包括%WIO

处理建议
通过上面的评估,可以确定大部分是由于 导致了数据库的物理读过高,从而使得系统反应变慢,处理方法就是关闭掉11g该新特性
alter system set event= ‘10949 trace name context forever, level 1’ scope=spfile;
重启数据库