Forward Recovery and Backward Recovery

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Overview of Forward and Backward Recovery in Database

Transaction modifies data that are stored in a Database. Transaction must always pass ACID Test. Transaction has to make sure the data in database remains consistence after it modifies the database. For example: Online payment when made has to have effects on both parties. The amount must be withdrawn from one account and must be deposited to another account. Or neither must happen. Only one of them must not happen in any circumstances. In such a case Database has to rollback the transaction.

When recovering the database, it is must redo the effects of the previous transactions. This is called Rolling Forward or simple Forward Recovery.

Let’s see the process of Rolling Forward or Forward Recovery:

Disk drive that was holding the data was crashed and you had backup copy that was 2 days older. Now you have to recover the lost data. You can use your log file to roll forward all the transaction that was completed but lost due to disk crash. This recovery process is called Rolling Forward or simple Forward Recovery.

Not all but some active transaction that didn’t complete successfully needs to rollback, when the disk drive crashed. Such kind of rollback is called Backward Recovery.

Mastering Database Recovery: Backward vs Forward Strategies

Embarking on the intricate journey of database management, the principles of backward and forward recovery emerge as stalwarts, ensuring the integrity and resilience of data. These concepts are integral components within the repertoire of database recovery mechanisms, offering a robust shield against the challenges posed by errors and failures. Let’s illuminate each of these strategies while seamlessly integrating key insights:

Backward Recovery:

Definition: In the realm of transactions that modify data within a database, adherence to the ACID test (Atomicity, Consistency, Isolation, Durability) is paramount. A transaction must guarantee that the data remains consistent after any modification. For instance, in the context of online payments, the impact must extend to both parties — the amount being withdrawn from one account and deposited into another. Either both these actions happen, or neither does. In case of an undesired outcome, the database triggers a rollback, a crucial aspect of backward recovery.

Use Cases:

  • Transaction Failures: Ensuring the database is restored to a consistent state when a transaction encounters errors or remains incomplete.
  • System Crashes: Mitigating the consequences of abrupt system crashes, restoring the database to a state consistent with the last recorded transaction.

Forward Recovery:

Definition: Forward recovery, also known as roll-forward recovery, becomes imperative when recovering a database involves redoing the effects of previous transactions. A practical scenario for forward recovery arises when a disk drive, holding crucial data, crashes, and the available backup copy is two days old. To recover the lost data, the log file becomes instrumental in rolling forward all completed transactions that were lost due to the disk crash.

Process of Forward Recovery:

  1. Identifying Lost Transactions: Only those transactions that were active but didn’t complete successfully need to be rolled back when a disk drive crashes. This type of rollback is aptly termed backward recovery.
  2. Rolling Forward: Leveraging the log file, the recovery process involves rolling forward or redoing transactions that were successfully completed but lost due to the disk crash.

Use Cases:

  • Transaction Commit: Ensuring that changes from successfully committed transactions, though not persisted due to a failure, are eventually applied.
  • Lost Updates: Addressing scenarios where updates or changes were not recorded, forward recovery facilitates the reapplication of these crucial changes.

Conclusion:

In summary, backward recovery meticulously undoes transactions to restore the database, while forward recovery focuses on reapplying lost changes. Both are indispensable components of a resilient database recovery strategy, safeguarding data integrity and system reliability in the face of failures. The interplay between these strategies often hinges on the nature of the failure and the desired outcome for ensuring database consistency.