偶尔发现数据库中发生如下等待事件，随查询文档整理出来：

control file sequential read

Reading from the control file. This happens in many cases. For example, while:

1、Making a backup of the control files

2、Sharing information (between instances) from the control file

3、Reading other blocks from the control files

4、Reading the header block

Wait Time: The wait time is the elapsed time of the read

Parameter	Description
file#	The control file from which the session is reading
block#	Block number in the control file from where the session starts to read. The block size is the physical block size of the port (usually 512 bytes, some UNIX ports have 1 or 2 Kilobytes).
blocks	The number of blocks that the session is trying to read

control file parallel write

This event occurs while the session is writing physical blocks to all control files. This happens when:

1、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)

2、The session commits a transaction to a control file

3、Changing a generic entry in the control file, the new value is being written to all control file

Wait Time: The wait time is the time it takes to finish all writes to all control files

Parameter	Description
files	The number of control files to which the session is writing
blocks	The number of blocks that the session is writing to the control file
requests	The number of I/O requests which the session wants to write

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控制文件相关的等待事件：control file sequential read / control file parallel write

control file parallel write

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