DG学习笔记(2)_体系结构

目录

1 Primary端Log Transport Services各个进程的作用

2 Standby 端Log Apply Services的各个进程的作用

1 Primary端Log Transport Services各个进程的作用

1.1 LGWR

LGWR collects transaction redo and updates the online redo logs. In synchronous mode it ships redo information directly to the RFS process on the standby database and waits for a confirmation before proceeding. In asynchronous mode, it ships the redo information directly as well, but doesn’t wait before proceedimg. (记录事务变化,传输日志到备库.什么时候传输? 同步?即事务一旦产生日志,就立即会传到备而不用等待归档来触发? The LGWR attribute indicates that redo is transmitted to the destination concurrently as the online redo log is written .)

1.2 ARCn

ARCn, or a SQL session performing an archival operation creates a copy of the online redo logs locally for use in a primary database recovery. The ARCn may also ship the redo stream to the RFS process while simultaneously archiving the online log, this is also responsible for proactively detecting and resolving gaps on all standby databases. (完成归档,并在归档的同时传输日志,并负责检测GAP.)

1.3 Fetch archive log Process

(FAL, Physical standby database only): FAL provides a client-server mechanism for resolving gaps. This process is only started when needed and shutdown as soon as it is finished.

The fetch archive log (FAL) client

The FAL client requests the transfer of archived redo log files automatically when it detects a gap in the redo logs received by the standby database.

The fetch archive log (FAL) client is the Oracle Net name of the standby site that is requesting a gap sequence. The initialization parameter for the FAL client is set on the standby site.

The FAL client pulls archived redo log files from the primary site and initiates and requests the transfer of archived redo log files automatically when it detects an archive gap on the standby database.

The FAL client and server are configured using the FAL_CLIENT and FAL_SERVER initialization parameters that are set on the standby location.(The parameters can also be set on the primary database in preparation for a future switchover operation.)

The FAL server typically runs on the primary database and services the FAL requests coming from the FAL client.

Even if you configure the primary database to archive automatically to the standby destination, you can still copy the completed archived redo logs manually if necessary.

即使你通过Log Transport Services配置了自动日志传输的方式,你仍可使用手工传输日志,再在Standby database Register 日志.

2 Standby 端Log Apply Services的各个进程的作用

2.1 Remote file server (RFS)

RFS process receives redo information from the primary database. For physical standby database only, RFS can optionally write the redo into standby redo logs or directly otherwis archived redo logs.Standby Redo Log必须手动创建. (RFS接收日志,并将其直接写到Standby redo Log,再由ARCn将其归档到Archive log. 或者直接将其写到Archive log. )

2.2 Archiver (ARCn) Process

For physical standby database only, the ARCn process archives the standby redo logs to be applied by the MRP.

2.3 Managed recovery process MRP

For physical standby databases only, the MRP applies archived redo log information to the physical standby database. If you start the managed recovery with the SQL statement ALTER DATABASE RECOVER MANAGED STANDBY DATABASE; this foreground session will do the recovery. If you use the optional clause: DISCONNECT [FROM SESSION] then the MRP background process will be started.

If you use Data Guard broker to manage your standbys, the broker will always startup the MRP background process for a physical standby database.(在物理Standby中,应用归档.)

2.4 Logical standby process(LSP)

For logical standby database only, the LSP controls the applying archived redo log information to the logical standby database.(在逻辑Standby中,以SQL的方式应用日志)