What are common database recovery methods?

Common database recovery methods include backup and restoration, transaction logging, shadow paging, and checkpointing.

Backup and restoration is a straightforward method of database recovery. Regular backups are made of the entire database or parts of it. In the event of a failure, the most recent backup is restored and the system is up and running again. This method is simple and effective, but it can be time-consuming if the database is large. It also requires sufficient storage space for the backups.

Transaction logging is another common method. Every change made to the database is recorded in a log. If a failure occurs, the log is used to 'undo' or 'redo' transactions to recover the database. This method is efficient and doesn't require as much storage space as backups. However, it can be complex to implement and maintain.

Shadow paging is a technique where changes are not immediately written to the database. Instead, they are made on a 'shadow' copy of the database page. If the transaction is successful, the shadow page becomes the actual page. If a failure occurs during the transaction, the original page is still intact and the system can recover easily. This method is efficient and provides a high level of data integrity. However, it can be complex to implement and may require additional storage space.

Checkpointing is a technique used in conjunction with transaction logging. At regular intervals, a 'checkpoint' is made and all transactions up to that point are guaranteed to be written to the database. In the event of a failure, only the transactions after the last checkpoint need to be considered for recovery. This reduces the time and complexity of the recovery process. However, it requires careful management to balance the frequency of checkpoints with system performance.

Each of these methods has its own advantages and disadvantages, and the choice of method depends on the specific requirements of the database system. In practice, a combination of these methods is often used to ensure robust and efficient recovery.