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.
- Redo applies uses a specialized process called the managed recovery process.
- 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.
- MRP is started in the physical standby database by mounting the database using below command.
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.
