Overview of Switchover and Failover in a Broker Environment

Oracle Data Guard helps you change the role of databases between primary and standby using either a switchover or failover operation.

  • A switchover is a role reversal between the primary database and one of its standby databases. A switchover guarantees no data loss and is typically done for planned maintenance of the primary system. During a switchover, the primary database transitions to a standby role, and the standby database transitions to the primary role.

  • A failover is a role transition in which one of the standby databases is transitioned to the primary role after the primary database (all instances in the case of an Oracle RAC database) fails or has become unreachable. A failover may or may not result in data loss depending on the protection mode in effect at the time of the failover.

The broker simplifies switchovers and failovers by allowing you to invoke them using a single key click in Oracle Enterprise Manager Cloud Control (Cloud Control) or a single command in the DGMGRL command-line interface (referred to in this documentation as manual failover). As part of managing the switchover, the broker automatically does the following:

  • Sets up redo transport from the new primary to the other members of the configuration

  • Starts Redo Apply services on the new standby

  • Ensures the other standbys in the broker configuration are viable to the new primary

  • Integrates with Oracle Clusterware and Oracle Global Data Services (GDS) to ensure that the proper services are started after a role change

When fast-start failover is enabled, the broker determines if a failover is necessary and initiates the failover to the current target standby database automatically, with no need for manual intervention. The reduced need for manual intervention can increase availability without increasing management costs. Manual failover gives you control over exactly when a failover occurs and to which target standby database. Regardless of the method you choose, the broker coordinates the role transition on all databases in the configuration.