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This illustration shows a Data Guard configuration during a switchover operation. The San Francisco database (originally the primary database) has changed to the standby role, but the Boston database has not yet changed to the primary role. At this point in time, both the San Francisco and Boston databases are operating in the standby role.
Applications that were previously sending read/write transactions to the San Francisco database are preparing to send read/write transactions to the Boston database. On the Boston standby database, the standby database online redo logs and local archived redo logs are still being generated. However, no redo logs are being sent or received over the Oracle Net network. Both of the standby databases are capable of operating in read-only mode.