Data Guard Switchover and Failover Tips Oracle Database Tips by Donald BurlesonDecember 9, 2015

Oracle Data Guard - Switchover and Failover

Introduction

A Oracle instance in a Data Guard configuration is created and maintained to transition into the role of the primary database in case of an emergency. In addition to a disaster recovery situation, the DBA may want to transition a Oracle instance into the primary role in order to perform certain types of maintenance activities on the original primary database. This process of role transition is facilitated using switchover and failover operations. This chapter will describe the role transition process in detail.

In brief, the switchover operation is a planned transition to allow maintenance work on the primary database. The failover is performed to re-establish database services if the primary database becomes unavailable and cannot be recovered within a reasonable period of time. Before deciding to activate a standby database using failover, the effects of the transition on your Data Guard configuration, the amount of time it will require for the transition, and the potential loss of data should be carefully examined.

In most cases, it is easier and more advantageous to recover the primary database than to use role transition. However, it should be noted that Data Guard technology is designed and intended to help in a disaster recovery situation.  Evaluate the failure scenario to determine if it requires a disaster recovery or if it can be repaired using traditional recovery operations.

The following figures show a graphical representation of role transition in a Data Guard environment. Figure 6.1 shows the usual working relationship between the primary and standby databases in the Data Guard environment. Figure 6.2 shows the transient state when the primary database is being switched over to a standby database, Standby DB1. Figure 6.3 shows the Data Guard environment after the switchover operation.

Figure 6.1 - One primary and two standby databases in Data Guard Environment