18 Questions
What is the main reason for needing database recovery?
To recover lost data after a system failure
Which of the following best describes the concept of database recovery?
Recovering lost data after a system failure
What is the primary focus of database backup methods?
Stable data processing and recovery
Which of the following actions is NOT part of database recovery?
Preventing data corruption
What is the purpose of the redo process in database recovery?
To reapply changes after a system failure
Which of the following is a common type of database failure that necessitates recovery?
System failure leading to data loss
What is the purpose of the 'Archive or dump' principle in database recovery?
To record old and new values of changing data.
Which type of database recovery action involves loading the most recent copy of the database and re-executing changes from the log?
Redo
What is the main objective of the 'Undo' process in database recovery?
To restore the database to its original state by canceling changes.
What technique involves faster recovery speed than log-based recovery?
Shadow paging technique
Which database troubleshooting technique involves checking logs to determine Redo and Undo actions?
Log-based technique
Which recovery technique involves simple Undo and no need for Redo?
Recovery using shadow page tables
In which scenario does the 'Redo' process come into play during database recovery?
To execute write operations again from the log for forward recovery.
In a distributed database, what protocol should be used to maintain the atomicity of multiple transactions?
2-phase commit protocol
What action is taken during 'Undo' in database recovery?
Restoring the database to its original state.
Which database system issue can occur when one site completes a transaction while the other site cancels the same transaction?
Data inconsistency
What causes overhead when using shadow page tables for recovery?
Copying and recording shadow page tables
Why is it difficult to use shadow paging alone when several transactions are executed simultaneously?
Complexity in maintaining atomicity
Study Notes
Database Recovery Techniques
- Redo technique uses redo and undo, and is slow due to checkpoint recovery.
- Undo technique is faster than redo, but it uses undo and no redo.
- Shadow paging technique is fast, but it's difficult to use alone when multiple transactions are executed simultaneously.
2-Phase Commit Protocol
- Used in distributed databases to maintain atomicity of transactions.
- Ensures either all participating databases complete the transaction or none of them do.
Database Recovery Principles
- Principle of information redundancy: uses archive or dump and log or journal to recover data.
- Archive or dump: copies and stores a database to another storage device.
- Log or journal: records old and new values of changing data each time a database is changed.
Database Recovery Actions
- Redo: uses archive copy and log to restore the database to its previous state after a commit.
- Undo: uses log and backward cancellation operation to restore the database to its original state before a commit.
Comparison of Database Recovery Techniques
- Log-based technique: uses log files for recovery, but is slow due to time delay.
- Shadow paging technique: uses shadow page tables, but has overhead due to copying and recording.
Database Troubleshooting
- Importance of database recovery: data can be corrupted due to problems, and restoring the database is vital for stable data processing.
- Recent trends: DBMS operates database backup policies, and backup methods are evolving continuously.
Learning Objectives
- Explain the concept and type of database failures.
- Explain the concept and methods of database recovery.
- Explain how to recover a distributed database.
- Explain and apply the types and characteristics of database backup methods.
Importance of Database Recovery
- IT-related losses can be significant, and data loss can cause serious damages to enterprises.
- Database recovery is necessary to restore lost data and resume online work quickly.
Test your knowledge on database recovery techniques such as Redo, Undo, log-based recovery, and shadow page tables. Learn about the advantages and disadvantages of each method in ensuring data consistency and availability.
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