等待事件：Disk file operations I/O

刘泽宇

ORALCE的等待事件有很多，今天在一个数据库的awr报告中发现了一个新的等待事件：Disk file operations I/O，官方解释如下：

This event is used to wait for disk file operations (for example, open, close, seek, and resize). It is also used for miscellaneous I/O operations such as block dumps and password file accesses.

Wait Time: The wait time is the actual time it takes to do the I/O

Parameter	Description
FileOperation	Type of file operation
fileno	File identification number
filetype	Type of file (for example, log file, data file, and so on)

我们知道操作系统在操作文件的时候，需要打开文件、关闭文件、定位文件位置等，当这些操作在进行的时候，Oracle就处于等待状态。

操作系统的这些文件操作可以划分如下：

1.file creation
2 file open
3 file resize
4 file deletion
5 file close
6 wait for all aio requests to finish
7 write verification
8 wait for miscellaneous io (ftp, block dump, passwd file)
9 read from snapshot files

以上的这些操作大部分跟操作系统的I/O有关系，跟数据库本身的参数等待是没有关系的，数据库出现Disk file operations I/O等待事件的时候往往也可以看到另外一个熟悉的等待事件：log file sync