Recovery Techniques: Log-Based and Shadow Paging Recovery techniques are essential for ensuring that database systems can continue operating efficiently afte...
Recovery techniques are essential for ensuring that database systems can continue operating efficiently after a system failure. These techniques involve storing and recovering transaction logs and checkpoint files to ensure that the system can reconstruct the state of the database and restore transaction processing from the latest successful checkpoint.
Log-Based Recovery:
A log file is created for each transaction.
Each log entry includes the following information:
Transaction ID
Timestamp
Database ID
Changes made to the database
Used for recovery, the log is replayed to reconstruct the state of the database.
Each database has its own log file.
The log files are written sequentially, ensuring that they are consistent in order.
Shadow Paging:
A shadow copy of the database is maintained.
Changes made to the original database are written to the shadow copy.
The shadow copy is stored on a different server or in a different storage medium.
When a failure occurs, the shadow copy is used to recover the database state.
The original database is then restored from the logs.
This approach is more complex to implement than log-based recovery, but it provides greater reliability and data integrity.
Benefits of Recovery Techniques:
Provides a mechanism for recovering the database to a consistent state after a system failure.
Ensures that the system can resume transaction processing from the latest successful checkpoint.
Simplifies disaster recovery by allowing the system to be restored quickly.
Comparison:
| Feature | Log-Based Recovery | Shadow Paging |
|---|---|---|
| Data consistency | High | Low |
| Reliability | High | Medium |
| Data integrity | High | Medium |
| Implementation complexity | Simpler | More complex |