The most important Data Guard Background processes

• Fetch Archive Log (FAL) Client - Pulls archived redo log files from the primary site. Initiates transfer of archived redo logs when it detects a gap sequence. 

• Remote File Server (RFS) - Receives archived and/or standby redo logs from the primary database. the Remote File Server (RFS) process receives the redo data and writes it to a Standby Redo Log (SRL). RFS sends an acknowledgement back to the production database that the redo has been received and written to disk. When the production database receives this acknowledgement, it acknowledges the commit to the client application and processes the next transaction. 

• Archiver (ARCn) Processes - Archives the standby redo logs applied by the managed recovery process (MRP).

• Managed Recovery Process (MRP) - Applies archive redo log information to the standby database.

• Logical Standby Process (LSP) - The LSP applies the redo records from archived redo logs to the logical standby database. The Oracle database log miner engine is used by the logical standby process for the SQL apply operations. Using the log miner engine, the LSP process recreates the SQL statements from redo logs that have been executed on the primary database. These statements are then applied to the standby database to keep it current with the primary database.