Expert Oracle Exadata - Parent Directory

CHAPTER 13 MIGRATING TO EXADATAintroduced a new product called Data Guard to manage and automate many of those tedious tasks ofmanaging and monitoring the Standby environment. Today Data Guard provides the following services:• Redo Transport Services• Handles the transmission of archived redo logs to the target system• Resolves gaps in archive redo logs due to network failure• Detect and resolve missing or corrupt archived redo logs by retransmittingreplacement logs• Apply Services• Automatically applies archived redo logs to the Standby database• Allows read-only access to the Standby database during redo apply• Provides role transition management: The role of the source and Standbydatabases may be switched temporarily or permanently.• Switchover: Temporarily switches the roles of the source and Standbydatabases. Useful for failing back a migration.• Failover: Permanent change in roles. Useful for finalizing the migration toExadata. The old source database becomes the standby and is kept in syncwith Exadata using Redo Apply.• Data Guard Broker:• Simplifies the configuration and instantiation of the Standby database.• Centralized console for monitoring and managing the Standby databaseenvironment.• Simplifies switchover/failover of the Standby database.Data Guard provides 3 modes of replication to the Standby database:Maximum Availability: Transactions in the source database don’t commit untilall redo necessary to recover the Standby are written to the online redo log andto the standby redo log.Maximum Performance: Transactions don’t commit until they are written tothe source online redo logs.Maximum Protection: Ensures zero data loss at the cost of performance on thesource database.Keep in mind that although Data Guard is an excellent tool for database migration, that is not itsonly purpose. Data Guard’s forte is protecting databases from media corruption, catastrophic mediafailure, and site failure. It is an integral component in Oracle’s Maximum Availability Architecture. So it’sno surprise that some of the replication modes mentioned above make no sense in the context ofdatabase migration. Maximum Performance is the replication mode most appropriate for migratingdatabases, because it has no impact on the performance of the source database. In Maximum459