Difference Between Switchover and Failover in Data Guard

In Oracle Data Guard, "Switchover" and "Failover" are two different concepts related to the role transition of the primary and standby databases in a Data Guard configuration. Here's an explanation of each:

1. Switchover:

Switchover is a planned and controlled role transition process in Oracle Data Guard. It allows you to switch the roles of the primary and standby databases while ensuring minimal downtime and data loss. During a switchover, the primary database is transitioned to become a standby database, and the standby database is transitioned to become the new primary database.

The switchover process involves synchronising the primary and standby databases, applying any pending redo data on the standby database, and then executing a role transition command to perform the switch. Switchover can be performed manually using SQL commands or by using Oracle Enterprise Manager (EM) Cloud Control.

Switchover is typically used for planned maintenance activities, such as upgrading hardware, applying patches, or performing other administrative tasks. It allows for a controlled transition without impacting the availability of the database.

2. Failover:

Failover, on the other hand, is an unplanned or emergency procedure in Oracle Data Guard. It is triggered when the primary database becomes unavailable or experiences a critical failure that prevents it from functioning properly. Failover enables the standby database to take over as the new primary database to ensure continuous availability of the database.

During a failover, the primary database is deemed inaccessible or inoperable, and the standby database is promoted to the primary role. The failover process involves initiating the role transition, applying any necessary redo data from the archived redo logs, and enabling the applications to connect to the new primary database.

Failover is typically used in situations where the primary database experiences a catastrophic failure, such as hardware failure, network outage, or data corruption. It aims to minimise downtime and ensure business continuity by quickly transitioning to the standby database as the new primary.

It's important to note that both switchover and failover are key features of Oracle Data Guard and provide mechanisms for maintaining high availability and data protection. Switchover is planned and controlled, while failover is an emergency procedure for unexpected failures. The choice between switchover and failover depends on the specific scenario and the requirements of the database environment.