Oracle 进程 简单介绍
Oracle 进程 简单介绍，SMON:在进行数据recovery的时候就是使用这个进程。这个进程主要负责对系统进行巡视，完成系统的清理，
对于Oracle每个进程的描述
比较重要的进程 SMON,PMON,DBWn,LGWR,CKPT,ARCn
SMON:在进行数据recovery的时候就是使用这个进程。这个进程主要负责对系统进行巡视，完成系统的清理，
PMON：用于对一些无效的连接进行清理，kill掉，创建新的必要的连接。
DBWn：完成SGA中的Data buffer cache 写入到 dbf data file 文件中。
在这些操作中会执行：
执行了checkpoint
脏数据达到了一定的程度（至的是SGA中的数据）
达到一定的时间（超过时间限制）
tablespace offline,read_only,online等操作
drop table的时候会触发
LGWR：用于对SGA中的 redo log buffer 写入到 redo.log中
在这些操作中会执行
要执行DBWn之前
执行 commit操作
在 log buffer 满了 1/3存储的时候
在超过1M的时候
每过3秒写入数据
CKPT:在数据写入到data files之前，，先在control file 里面做记录。
可以确保 数据库的恢复。在执行这个操作的时候，DBWn,LGWR等都会工作，
把数据写入到数据文件和日志文件
ARCn：在开启归档模式（archive log list， alter database archivelog/noarchivelog）的时候。
系统会把redo.log里面的数据写入到 archive log中。用于 rman 数据恢复
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