Standby Redo Logs (SRL)

 These are required to enable real time apply of redo data onto the standby.  the standby redo logs are populated with redo information as fast as the primary redo logs, rather than waiting for the redo log to be archived and shipped to the standby. So the loss of data in the event of a failover is minimized.

On the standby database Oracle Data Guard uses the Remote File Server(RFS) process to receive the redo records from the primary database, the Managed Recover Process(MRP) to apply redo information to the physical standby database.

when Real Time Apply,is enabled,MRP reads redo data directly from the currrent standby redo log file as it is being filled up by the RFS process.

When Real Time Apply is not enabled, the MRP reads from archive log and apply the redo data to the physical standby database.

when standby database doesn’t have SRL, the archive log files are shipped to the standby database from the primary and then the MRP reads it and applies the redo data to the physical standby

To Add Standby redo log

SQL> ALTER DATABASE ADD STANDBY LOGFILE THREAD 10
  ('/oracle6/bhuvan/redo/log10a.rdo','/oracle7/bhuvan/redo/log10b.rdo') SIZE 1024M;

To Verift Standby Redo Logs

V$STANDBY_LOG;