A hot standby system consists of one master instance and one or more standby instances that reproduce the changes to the master instance at regular intervals. Master and standby instances form a cluster (see Architecture of a Hot Standby System) that, outwardly, behaves like a single database instance.
The standby instances are in the STANDBY operational state, which corresponds to a state between ADMIN and ONLINE. In this state, they are not full-fledged database instances (they do not, for example, write log entries).
If a master instance fails due to a hardware or logical error, one of the standby instances automatically becomes the new master instance (see Behavior of the Hot Standby System when Errors Occur).
Advantage of a hot standby system when errors occur:
? very short downtime (considerably faster than restarting the master instance)
A hot standby system does not offer any protection against errors and inconsistencies caused by the user or an application. To secure yourself against these types of errors, you have to execute regular data and log backups, even in a hot standby system (see Backing Up and Restoring).
1. You configure the computers on which the master and standby instances comprising the hot standby system will later be located as a cluster. For information on configuring the cluster, see the documentation for your cluster software.
2. Using the cluster software, you define a virtual server name with which the database is to be addressed externally. The virtual server name may not be the same as the name of a computer in the cluster.
3. You install a memory management system. For information on configuring the memory management system, see the manufacturer’s documentation.
4. You create a database instance on the computer that you have defined as the virtual server.
The volumes of the database instance must be in the memory management system.
5. You configure the database instance as the master instance of the hot standby system.
6. You add one or more standby instances.
0 Database Manager CLI, Managing Hot Standby Systems
7. The database system updates the standby instances at regular intervals by importing the redo log entries of the master instance (see Synchronization of Master and Standby Instances).
Database Management Tutorial, Setting Up-the Hot Standby-System