Oracle Data Guard provides high availability for mission critical databases. Data protection is one of the critical aspects in any organization. Oracle Data Guard provides protection for enterprise data as a result of any infrastructure issues. It enables administrators to bring up an affected database on a standby location with minimal downtime.
Architecture
A Data Guard configuration can contain one primary and multiple standby databases. Using Data Guard, you can switch any standby database to a primary role with minimum downtime. In Oracle 19c, Data Guard can support up to 30 standby instances. The standby databases can be either physical, logical, or snapshot instances.
1) Primary Database
A Primary Database is a database instance that is opened for read/write access and is where most of the applications are connected. It can be a single or a RAC instance.
2) Standby Database
A Standby Database is a copy of a Primary Database. It can be a physically identical copy of the Primary Database (Physical Standby Database) or it can contain the same logical information as the Primary Database (Logical Standby Database). Like the Primary Database, the Standby Database can also be a single instance or a RAC instance.
Beginning with Oracle 11G, a Physical Standby Instance can be started in read-only mode to use the instance for reporting purposes.
In addition, you can use a Secondary Network for redo transfers so you don’t bottleneck the Primary Network with redo transfers which are typically used by users to access the primary database and its applications.
Data Guard Services
Data Guard helps automate redo transfers from the Primary to the Standby Server and apply the same to the Standby Instance.
You can also change the Database Role using a Switchover or Failover Operation. A Switchover Operation can be utilized when both the Primary and Standby Databases are accessible. During a switchover the Primary database would become the Standby Database and the Standby Database would become the Primary Database. A Failover Operation is utilized when the Primary Database is not accessible due to an outage.
Data Guard Protection Modes
Data Guard can also be configured in Maximum Performance or Maximum Protection mode.
1) Maximum Performance
In Maximum Performance mode, transactions are committed as soon as the data has been written to the Online Redo Log.
2) Maximum Protection
In Maximum Protection mode, transactions are committed as soon as the data has been written to the Online Redo Log and Standby Redo Log on at least one Standby Server. If an acknowledgement in not received from a Standby Database, the transactions would not be committed on the Primary Database.
There is one additional protection mode, Maximum Availability, in which the Primary Database will wait until a predetermined threshold time to receive an acknowledgement from the Standby Database after which the data would be committed in the Primary Database.
Conclusion
Oracle Data Guard ensures high availability, data protection, and disaster recovery for enterprise data. It provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases to enable Oracle databases to survive disasters and data corruption. With Oracle Data Guard, administrators can optionally improve production database performance by offloading resource-intensive backup and reporting operations to standby systems.