Oracle Process Architecture - Oracle 进程结构篇4

前言：接上一篇 Oracle Process Architecture - Oracle 进程结构篇3

          http://blog.csdn.net/nature_ann/article/details/12710827

1.Optional Background Processes可选的后台进程

<<----可选的后台进程是一些没有被强制定义的后台进程。大多数的可选后台进程包含特殊的任务或特性。比如某些后台进程，在它们是有效的情况下，支持 Oracle Streams AQ或Oracle ASM。 ---->>

An optional background processis any background process not defined as mandatory. Most optional background processes are specific to tasks or features. For example, background processes that support Oracle Streams  Advanced Queuing (AQ) orOracle Automatic Storage Management(Oracle ASM) are only available when these features are enabled.

<<----下面是一些常见的可选进程：ARCn,CJQO and Jnnn,FBDA,SMCO---->>

This section describes some common optional processes:

>>Archiver Processes(ARCn)

>>Job Queue Processes(CJQO and Jnnn)

>>Flashback Data Archiver Process(FBDA)

>>Space Management Coordinator Process(SMCO)

1.1  Archiver Processes –ARCn 归档进程

<<----归档进程，在日志切换发生时，拷贝在线重做日志，离线存储。归档进程还收集事务重做数据并且传输它到standby数据库。归档进程只有在数据库是归档模式和自动归档被设置为enabled时才存在。---->>

The archiver processes (ARCn) copy online redo log files to offline storage after a redo log switch occurs. These processes can also collect transaction redo data and transmit it to standby database destinations. ARCn processes existonly when the database is in ARCHIVELOG mode and automatic archiving is enabled.

1.2 Job Queue Processes –CJQ0 and Jnnn 作业队列进程

<<----Oracle数据库使用作业队列进程来运行用户作业，通常使用批处理模式。作业是由用户定义的任务，被调度一次或多次。例如，你可以使用一个作业队列来定制一个在后台长时间运行更新的任务。设定一个开始时间和一个时间间隔，这个作业队列进程尝试在下一个间隔时间发生时运行该作业。---->>

Oracle Database uses job queue processes to runuser jobs, often inbatch mode. A job is a user-defined taskscheduled to run one or more times. For example, you can use a job queue toschedule a long-running update in the background. Given a start date and a time interval, the job queue processes attempt to run the job at the next occurrence of the interval.

 

<<----Oralce数据库动态管理作业队列进程，在作业队列客户端有需要时，能使用更多的作业队列进程。当这些进程处于空闲时，数据库会释放资源给新的进程使用。 ---->>

Oracle Database manages job queue processes dynamically, thereby enabling job queue clients to use more job queue processes when required. The database releases resources used by the new processes when they are idle.

<<---- 动态作业队列进程可能会在一个指定的时间间隔里，大量的作业被同时运行。事件运行的顺序如下：1.Oracle调度器根据需要会自动启动和停止作业协调器进程(CJQ0).协调器进程定期的从系统JOB$表中选择需要运行的作业。被选出来的新作业按时间排序。2.协调器进程动态派生出作业队列从属进程(Jnnn)来运行作业。3.作业队列进程运行由CJQ0(作业协调器进程)选出用来运行的某个作业。每一个作业队列进程一次运行一个作业直到完成。4.当进程完成单个作业的执行后，将会轮询更多的作业。如果没有作业被调度执行，则它进入睡眠状态，且在周期性醒来时再次轮询更多的作业。如果进程没有发现新的作业，那么它会在一个预设的间隔时间后悔终止。---->>

Dynamic job queue processes can run a large number of jobs concurrently at a given interval. The sequence of events is as follows:

>>Thejob coordinator process (CJQ0) is automatically started and stopped as needed by Oracle Scheduler. The coordinator process periodically selects jobs that need to be run from the systemJOB$ table. New jobs selected areordered by time.

>>The coordinator processdynamically spawnsjob queue slave processes (Jnnn) to run the jobs.

>>The job queue process runs one of the jobs that was selected by theCJQ0 process for execution. Each job queue process runsone job at a time to completion.

>>After the process finishes execution of asingle job, it polls for more jobs. If no jobs are scheduled for execution, then it enters asleep state, from which itwakes up at periodic intervals and polls for more jobs. If the process does not find any new jobs, then itterminates after a preset interval.

<<----初始化参数JOB_QUEUE_PROCESSES可以设定在一个实例上同时运行的作业队列进程的最大数目。然而，客户端不应假定所有作业队列进程都可用于执行作业。 ---->>

The initialization parameterJOB_QUEUE_PROCESSES represents the maximum number of job queue processes that can concurrently run on an instance. However, clients should not assume that all job queue processes are available for job execution.

1.3 Flashback Data Archiver Process –FBDA 闪回数据归档进程

<<----闪回数据归档进程将跟踪表的历史行到闪回数据归档区。当跟踪表中包含DML事务提交时，该进程将存储行的前镜像到闪回数据归档区。然而，它也会保存当前行上的元数据。 ---->>

The flashback data archiver process (FBDA) archives historical rows of trackedtables into Flashback Data Archives. When a transaction containing DML on a tracked table commits, this process stores thepre-image of therows into the Flashback Data Archive. It also keeps metadata on the current rows.

<<----闪回数据归档进程管理闪回数据归档区的空间、组织和保留期等。此外，该进程还记录被跟踪的事务归档已经发生了多长时间。---->>

FBDA automatically manages theflashback data archive forspace, organization, andretention. Additionally, the processkeeps track of how far thearchiving of tracked transactions has occurred.

1.4 Space Management Coordinator Process –SMCO 空间管理协调器进程

<<---- 空间管理协调进程协调各种空间管理相关的执行任务。比如主动预防性空间的分配和空间回收。SMCO进程动态派生出从属进程(Wnnn)来执行此任务。---->>

The SMCO process coordinates the execution of various space management relatedtasks, such as proactive spaceallocation and spacereclamation. SMCO dynamically spawnsslave processes (Wnnn) to implement the task.

 

待续。。