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Jun 07, 2016 pm 04:10 PM

Backstagestart upExampletidyterminationrunprocess

实例后台进程在启动实例时启动，在终止实例时终止运行。 1.SMON 起初的任务是安装和打开数据库。SMON通过查找和验证数据库控制文件来安装数据库。此后，通过查找和验证所有的数据文件和联机日志文件打开数据库。一旦打开数据库并使数据库处于使用状态后，SM

实例后台进程在启动实例时启动，在终止实例时终止运行。

1.SMON

起初的任务是安装和打开数据库。SMON通过查找和验证数据库控制文件来安装数据库。此后，通过查找和验证所有的数据文件和联机日志文件打开数据库。一旦打开数据库并使数据库处于使用状态后，SMON就负责执行各种内部管理任务，如合并数据文件中的可用空间。

2.PMON

PMON监视所有服务器进程，并检测会话中的任何资源。如果会话异常终止，PMON将销毁服务器进程，将其PGA内存返回给操作系统的空闲内存池，并回滚任何尚在进行的未完成事务。

3.DBWn

会话将数据写入数据库缓冲区缓存中的缓冲区，DBWn将数据库缓冲区缓存中的数据写入磁盘。

注：在提交事务的时候，DBWn有什么举动？什么都不做！

4.LGWR&ARCn

LGWR将日志缓冲区中的内容写到磁盘上的联机日志文件中，ARCn将联机日志文件中的内容写到归档日志文件中。

5.CKPT

负责发出普通检查点的信号，激发DBWn。从8i开始，DBWn用增量检查点替代了完全检查点。

注：何时发生完全检查点？只会应要求这么做，或在有序关闭数据库的时候出现。

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