Oracle Dataguard background process, log apply service internals

Dataguard Background process:

1.       Logwriter process

2.       Archiver process

3.       Logwriter network server (LNS)

4.       Fetch archive logs (FAL) For client server mechanism

5.       Remote file server

6.       Managed recovery process for physical standby

7.       Logical standby process for logical standby

8.       Data guard broker monitor (DMON) – If incase dg broker enabled

Apply services at High Level: -          Data guard apply services comprises of two parts

o   Redo Apply for physical standby

o   Sql Apply for logical standby

-        The Physical standby and logical standby databases utilize the same redo transport and role management services, only apply service is different.

Redo apply: A physical standby database applies redo data received from the primary database using oracle media recovery process.

1.    Redo applies uses a specialized process called the managed recovery process.
2.   As the RFS process is writing redo data to standby redo logs (SRL’s). MRP process reads the redo data and applies it to the physical standby database.
3.    MRP is started in the physical standby database by mounting the database using below command.

-          Sql > alter database recover managed standby database using current logfile disconnect from the session;

Sql Apply: Sql apply uses a collection of background process that perform the task of applying changes from the primary database to the logical standby database.

 Logical standby database:

• -          Logical standby database contains the same logical information at standby DB.
• -          Physical organization and structure of the data can be different.
• -          Synchronization with the primary database through sql apply.
• -          Can be used for queries and reporting at any time.

-         Service to be involved for logical standby : Log transport services, Log apply services

Log Transport services:  Transmit the redo data from the primary database to standby. Enforce the data protection modes.

Log apply services: Automatically apply the archived redo logs on the standby database. Maintains transitional synchronization with primary database. Allows transitionally consistent read-only access to the data.