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Standby (DG) – Processes Explained.

Posted by FatDBA on August 27, 2012

SQL> SELECT PROCESS, STATUS FROM V$MANAGED_STANDBY;

PROCESS   STATUS
——— ————
ARCH      CONNECTED
ARCH      CONNECTED
RFS         IDLE
MRP0    WAIT_FOR_LOG

RFS: Is Remote File Server. RFS process writes the redo data to either archived redo log files or standby redo log files. the RFS process writes the redo data to either archived redo log files or standby redo log files. However, if you use standby redo log files, you can enable real-time apply, which allows Data Guard to recover redo data from the current standby redo log file as it is being filled up by the RFS process.

lgwrsync1

LGWR SYNC Archival to a Remote Destination with Standby Redo Log Files

————————

lgwrasync2

LGWR ASYNC Archival with Network Server (LNSn) Processes

 

Real Time Feature: If the real-time apply feature is enabled, log apply services can apply redo data as it is received, without waiting for the current standby redo log file to be archived. This results in faster switchover and failover times because the standby redo log files have been applied already to the standby database by the time the failover or switchover begins.

Use the ALTER DATABASE statement to enable the real-time apply feature, as follows:

  • For physical standby databases, issue the ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE statement.
  • For logical standby databases, issue the ALTER DATABASE START LOGICAL STANDBY APPLY IMMEDIATE statement.

MRP/MRP0: Stands for Managed Recovery Process and sits between Standby Database and redo-log files/Archives redo. MRP is the process which will apply the changes from standby redolog files to standby database.

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