DG學習筆記(2)_體系結構

DG學習筆記(2)_體系結構

 

目錄

1 Primary端Log Transport Services各個程式的作用

2 Standby 端Log Apply Services的各個程式的作用

 

 

 

1 Primary端Log Transport Services各個程式的作用

 

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. (記錄事務變化,傳輸日誌到備庫.什麼時候傳輸? 同步?即事務一旦產生日誌,就立即會傳到備而不用等待歸檔來觸發? 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. (完成歸檔,並在歸檔的同時傳輸日誌,並負責檢測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.

即使你透過Log Transport Services配置了自動日誌傳輸的方式,你仍可使用手工傳輸日誌,再在Standby database Register 日誌.

 

 

2 Standby 端Log Apply Services的各個程式的作用

 

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必須手動建立. (RFS接收日誌,並將其直接寫到Standby redo Log,再由ARCn將其歸檔到Archive log. 或者直接將其寫到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,應用歸檔.)

 

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.(在邏輯Standby中,以SQL的方式應用日誌)