Oracle Process Architecture - Oracle 进程结构篇2

前言：接上一篇 Oracle Process Architecture - Oracle 进程结构篇1

            http://blog.csdn.net/nature_ann/article/details/11071477

1.Background Processes

<<----一个多进程Oracle数据库使用的一些附加的进程被称为后台进程。它执行维护操作数据库和多用户最大限度地提高性能所需的任务。---->>

A multiprocess Oracle database uses some additional processes called
background processes. The background processes perform
maintenance tasks required to operate the database and to maximize performance for multiple users.

 <<----每一个单独进程有一个单独的任务，但是与其他进程一起工作。例如：LGWR进程把数据从日志缓冲区写入在线重做日志。当一个写满的日志文件被归档的时候，LGWR会发一个信号给另一个进程，归档文件。---->>

Each background process has a separate task, but works with the other processes. For example, the LGWR process writes data from the
redo log buffer to the
online redo log. When a filled log file is ready to be archived,LGWR  signals another process to archive the file.

<<----当一个数据库实例开启时，oracle
数据库的后台进程被自动创建。一个实例会有很多后台进程，但不是所有的后台进程都存在于每一个数据库配置当中，下面的查询语句可以获取当前数据库的进程列表---->>

Oracle Database creates background processes automatically when a database instance starts. An instance can have many background processes, not all of which always exist in every database configuration.
The following query lists the background processes running on your database:

Select pname from v$process where pname is not null order by pname.

1.1 Mandatory background Processes

<<----必需的后台进程是存在于所有的典型数据库配置中。这些进程默认运行在使用最小化参数配置文件启动的数据库实例中。---->>

The mandatory background processes are present in all typical database configurations. These processes run by default in a database
instance started with a minimally configured initialization parameter file.

<<----这些进程包括：进程监控进程PMON，系统监控进程SMON，数据库写进程LGWR，检查点进程CKPT，管理监控进程MMON
and MMNL，回收进程RECO--->>

This section describes the following mandatory background processes:

Process Monitor Process(PMON)

System Monitor Process(SMON)

Database Writer Process(LGWR)

Checkpoint Process(CKPT)

Manageability Monitor Processes(MMON and MMNL)

Recoverer Process(RECO)

1.1.1 Process Monitor Process –PMON

<<----PMON监控其他后台进程并在一个服务或调度进程异常终止时执行进程恢复。PMON进程负责清理数据库高速缓冲区和释放被使用的客户端进程资源。例如：重置在线事务表的状态，释放无用锁，从活动进程列表中移除进程ID。---->>

The process monitor (PMON) monitors the other background processes and performs
process recovery when a server or dispatcher process terminates abnormally. PMON is responsible for cleaning up the database buffer cache
and freeing resources that the client process was using. For example, PMON resets the
status of the active transaction table,
releases locks that are no longer required, and removes the process ID from the list of active processes.

<<----PMON也注册有关实例与Oracle Net listener
的调度进程的信息。当一个实例开启时，PMON进程监测监听决定是否运行它。如果监听是运行的，PMON跳过相关的参数，如果不是运行的，PMON周期性的尝试联系它。---->>

PMON also registers information about the instance and dispatcher processes with the
Oracle Net listener. When an instance starts, PMON
polls the listener to determine whether it is running. If the listener is running, then PMON passes it relevant parameters. If it is not running, then PMON periodically attempts to contact it.

1.1.2 System Monitor Process –SMON

<<---- SMON负责各种系统级别的清理职责。分配给SMON的职责如下：---->>

The system monitor process (SMON) is in charge of a variety of system-level cleanup duties. The duties assigned to SMON include:

<<---1.执行实例恢复：如果有必要，在实例启动时。在RAC数据库，一个数据库实例的SMON进程对发生故障的实例执行实例恢复。---->>

>>Performing instance recovery, if necessary, at instance startup. In an Oracle RAC database, the SMON process of one database instance
can perform instance recovery for a failed instance.

<<---2.恢复终止的事务：那些在实例恢复期间由于文件读或表空间是offline状态发生的错误被跳过的事务。SMON进程恢复这些事务当表空间或文件是online的时候。
---->>

>>Recovering terminated transactions that were skipped during instance recovery because of file-read or tablespace offline errors.
SMON recovers the transactions when the tablespace or file is brought back online.

<<---3.清理不用的临时段：比如，Oracle数据库创建索引时分配区，如果操作是有误的，SMON进程负责清理临时表空间。
---->>

>>Cleaning up unused temporary segments. For example, Oracle Database allocates extents when creating an index. If the operation fails, then SMON cleans up the temporary space.

<<---4. 合并连续的空闲的区，在数据字典管理的表空间里。---->>

>>Coalescing contiguous free extents within dictionary-managed tablespaces.

<<---SMON进程会定期检查，去看看是否被需要的，其他的进程可以呼叫SMON进程在他们发现需要smon帮助的时候。---->>

SMON checks regularly to see whether it is needed. Other processes can call SMON if they detect a need for it.

 

待续。。。