在数据库某份AWR的Backgroud Wait Events报告中发现关于控制文件的等待事件，因为是第一次遇见，而且占的bg time比例很大，让我们来一探究竟关于控制文件的事件。
首先，当session把物理块写入控制文件的时候发生control file parallel write事件，发生在是进程DBWR上，取决于DBWR把信息写入控制文件的时间。
其产生的原因如下：

The session starts a control file transaction (to make sure that the control files are up to date in case the session crashes before committing the control file transaction)
The session commits a transaction to a control file
Changing a generic entry in the control file, the new value is being written to all control files

可行的方案是

Reduce the number of controlfile copies to the minimum that ensures that not all copies can be lost at the same time.
Use Asynchronous I/O if available on your platform.
Move the controlfile copies to less saturated storage locations.

当然也需要检查一下logfile文件是否被过度的交换使用，在视图v$loglist 视图中检查logfie的使用频率。如果logfile太小，考虑增大避免logfile频繁交换。

点击(此处)折叠或打开

alter database drop logfile group 3;
ALTER DATABASE ADD LOGFILE THREAD 1 GROUP 3 '/oracle/oradata/CURACAO9/redo03.log' size 500m reuse;
ALTER DATABASE ADD LOGFILE member '/oracle/oradata/CURACAO9/redo03b.log' reuse to GROUP 3;
alter system switch logfile;
alter system checkpoint;
alter database drop logfile group 2;

对于control file sequential read事件，控制文件是顺序写的，当然在读取的时候也是顺序读的，该事件就是读控制文件消耗的时间
产生的原因

Making a backup of the controlfiles
Sharing information (between instances) from the controlfile
Reading other blocks from the controlfiles
Reading the header block

Control file sequential read waits occur when the control files are placed on the same physical disk, causing read-write head contention at the disk level.

Move the problematic controlfile copy to a less utilized disk. Use Asynchronous I/O if available.

当我检查以上信息时，不等不承认系统I/O瓶颈严重。

参考一下内容：
https://community.oracle.com/thread/370520?start=0&tstart=0
http://www.dba-oracle.com/m_control_file_parallel_write.htm
http://www.askmaclean.com/archives/control-file-sequential-read.html

ITPub博客

control file parallel write 和control file sequential read 等待事件

最新文章