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All distributed databases are set up a bit differently, even among a single software vendor's products. With Microsoft, for example, Microsoft Exchange Server, SQL Server and Active Directory are all database-driven, but function differently from one another. But there are some similarities that more or less hold true across the board.
When it comes to distributed database recovery, there are two primary concerns that must be addressed:
- Data integrity. The distributed database must be restored or repaired in such a way that no corruption exists. Generally speaking, this requires the distributed database recovery process to be application-aware. The software used by the recovery operation has to know the specific requirements of the database being recovered. For example, most enterprise-class backup applications support Exchange Server. This Exchange Server support means the backup application knows how to handle database checkpoints and process transaction logs as a part of the recovery process.
- Point-in-time recovery. For example, if you are recovering an Active Directory database on a domain controller, you may wish to roll the Active Directory back to a specific point in time. The problem is that Active Directory uses a distributed database and other domain controllers are online. When the distributed database recovery process is complete, the newly restored domain controller will reach out to other domain controllers and initiate a synchronization process. This brings the newly restored domain controller to a current state that is consistent with the other domain controllers. If your goal was to roll Active Directory back to an earlier point in time, the synchronization process will undo your recovery efforts. The solution for the distributed databases is to perform an authoritative recovery, which essentially causes the newly restored domain controller to be treated as the correct copy of the Active Directory database.
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