Database Systems Quiz
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Questions and Answers

What is the primary purpose of database recovery?

  • To enhance database performance
  • To implement security measures
  • To restore the database to a correct state after a failure (correct)
  • To manage user access and permissions

    • Which type of storage is characterized by the inability to retain information after a system crash?

  • Stable storage
  • Cloud storage
  • Nonvolatile storage
  • Volatile storage (correct)

    • Which failure is categorized under system failures?

  • Application software errors
  • Natural disasters
  • Data sabotage
  • Power failure (correct)

    • What results from transaction failure?

    <p>The transaction is aborted and might be restarted</p> Signup and view all the answers

    What forms of failure can result in data inconsistency visible to transactions?

    <p>All forms of failures including application errors and sabotage</p> Signup and view all the answers

    Which of the following is considered a type of media failure?

    <p>Loss of secondary storage components</p> Signup and view all the answers

    What is a key feature of stable storage?

    <p>It guarantees persistence through independent failure modes</p> Signup and view all the answers

    Which one is not considered a type of failure in database systems?

    <p>Design failure</p> Signup and view all the answers

    What is the first step in performing a database recovery?

    <p>Isolating the database from other users</p> Signup and view all the answers

    What does the recovery manager ensure during a transaction recovery?

    <p>Atomicity and durability properties</p> Signup and view all the answers

    Which type of failure requires removing the effects of completed transactions from the database?

    <p>System failure</p> Signup and view all the answers

    If a transaction was not committed at failure time, what does the recovery manager do?

    <p>Rollback the effects of the transaction</p> Signup and view all the answers

    What facility should a DBMS provide to track the current state of transactions?

    <p>Logging facility</p> Signup and view all the answers

    Which recovery technique is applied last in the basic recovery steps?

    <p>Applying transaction log dumps</p> Signup and view all the answers

    What is a global undo in the context of database recovery?

    <p>Undoing all effects of all transactions</p> Signup and view all the answers

    When must a backup mechanism be implemented in a DBMS?

    <p>To create periodic backup copies of the database</p> Signup and view all the answers

    What recovery technique is used when updates are not recorded until after a transaction reaches its commit point?

    <p>Deferred Update</p> Signup and view all the answers

    In which scenario is a backup not required for database recovery?

    <p>If the database is inconsistent but has no physical damage</p> Signup and view all the answers

    What needs to happen for an immediate update to be applicable?

    <p>The updates must occur simultaneously with transaction commitments.</p> Signup and view all the answers

    What is a requirement after a failure when using immediate update?

    <p>Redo updates of committed transactions need to be performed.</p> Signup and view all the answers

    Which statement best describes shadow paging?

    <p>It involves maintaining a separate copy of the database pages.</p> Signup and view all the answers

    What happens if a transaction aborts in the deferred update method?

    <p>The log record for the transaction is ignored.</p> Signup and view all the answers

    What method is associated with making updates only on a local transaction workspace until a commit?

    <p>Deferred Update</p> Signup and view all the answers

    What is a key characteristic of the NO-UNDO/REDO algorithm?

    <p>No undo operation is necessary if a transaction fails.</p> Signup and view all the answers

    What is the process called when an updated buffer is written before a transaction commits?

    <p>Steal</p> Signup and view all the answers

    Which phase of the recovery process reads the last checkpoint record to identify active transactions?

    <p>Analysis phase</p> Signup and view all the answers

    What is the purpose of the write-ahead log protocol?

    <p>To allow the database to recover from failures by writing log records before database updates.</p> Signup and view all the answers

    What is the term used for pages that have been modified in memory but not yet written to disk?

    <p>Dirty pages</p> Signup and view all the answers

    In the UNDO/REDO algorithm, which operation is performed first during recovery?

    <p>Undo the changes made by uncommitted transactions.</p> Signup and view all the answers

    What does the force approach in database management entail?

    <p>Immediately writing updated pages to disk upon transaction commit</p> Signup and view all the answers

    What characterizes the Shadow Paging recovery technique?

    <p>It uses two page tables: a current and a shadow page table for recovery.</p> Signup and view all the answers

    What principle of the ARIES recovery algorithm ensures that all changes to a database object are logged before they are written to disk?

    <p>Write-ahead logging</p> Signup and view all the answers

    What does the ARIES recovery algorithm handle in a steal, no-force approach?

    <p>Recovery for databases where cache page updates may not be written before commit.</p> Signup and view all the answers

    Which phase follows the analysis phase in the recovery process?

    <p>Redo phase</p> Signup and view all the answers

    Which of the following is true regarding the UNDO/NO-REDO algorithm?

    <p>It undoes changes but does not apply any completed operations.</p> Signup and view all the answers

    During which phase of the ARIES recovery process are transactions that did not commit undone?

    <p>Undo phase</p> Signup and view all the answers

    What happens if there is no commit record for a transaction after a failure?

    <p>The transaction is considered active and must be undone.</p> Signup and view all the answers

    What occurs during the repeat history step of the redo phase in the ARIES algorithm?

    <p>All actions prior to the crash are retraced</p> Signup and view all the answers

    What is a potential drawback of using the Shadow Paging technique?

    <p>It incurs overhead related to page management and replacements.</p> Signup and view all the answers

    What does the pin-unpin bit indicate in the ARIES recovery algorithm?

    <p>Whether a page can be written back to disk.</p> Signup and view all the answers

    What type of transaction is specifically mentioned that can access multiple databases?

    <p>Multidatabase transaction</p> Signup and view all the answers

    What data structure maintains information about all transactions that are currently active?

    <p>Transaction table</p> Signup and view all the answers

    What is a necessary component in maintaining the atomicity of a multidatabase transaction?

    <p>Global recovery manager</p> Signup and view all the answers

    What does the global recovery manager send to each participant in Phase 1 of the two-phase commit protocol?

    <p>Prepare for commit</p> Signup and view all the answers

    What is indicated by a 'cannot commit' signal from a participating database?

    <p>The local transaction cannot commit for some reason.</p> Signup and view all the answers

    Which of the following best describes the dirty page table?

    <p>Contains entries for modified but unwritten pages</p> Signup and view all the answers

    In a multidatabase system, what types of DBMSs might be involved?

    <p>Relational, object-oriented, hierarchical, and network</p> Signup and view all the answers

    What happens if the force-writing to disk fails during Phase 1 of the two-phase commit protocol?

    <p>A cannot commit signal is sent to the coordinator.</p> Signup and view all the answers

    Study Notes

    Database Recovery Techniques

    • Database recovery is the process of restoring a database to a correct state after a failure. It aims to eliminate the effects of the failure from the database, effectively restoring the last consistent state of the data items.

    Recovery Concepts

    • Recovery techniques vary based on how updates are handled.

    Recovery Concepts Based on Deferred Update

    • Updates are not written to the database until after a transaction reaches its commit point.
    • If a transaction fails before commit, it does not modify the database, so undoing changes isn't required.
    • Updates of committed transactions may need to be redone as their effects might not have reached the database yet.
    • If a transaction aborts, the log record for it is ignored, and no actions are taken on that transaction.

    Recovery Concepts Based on Immediate Update

    • Updates are applied to the database as they occur.
    • Redoing updates of committed transactions might be needed after a failure.
    • Undoing effects of uncommitted transactions might also be required.
    • Log records must be written before writing to the database (write-ahead logging).
    • If a transaction did not commit before the failure, it needs to be undone.
    • Undo operations are performed in reverse order.

    Shadow Paging

    • Two page tables are maintained: current page and shadow page.
    • Initialization: current page and shadow page tables are identical.
    • The shadow page table remains unchanged throughout the transaction.
    • The current page table logs all updates during a transaction.
    • After completion, the current page table becomes the shadow page.
    • No log record management is needed.
    • Page replacement management is necessary.

    The ARIES Recovery Algorithm

    • Recovery algorithm designed for a steal, no-force approach to recovery operations.
    • Useful for databases that use STEAL and NO-FORCE policies (memory management techniques).
    • If a cache page updated by a transaction cannot be written to disk before the transaction commits, this is called 'no-steal'.

    Recovery in Multidatabase Systems

    • In multidatabase transactions, access is made to multiple databases possibly with varying DBMS types.
    • Each DBMS may have its unique recovery technique, independent of the others.
    • Implementing atomicity in a multidatabase requires a two-level recovery mechanism.
    • A global recovery manager (coordinator) is required to maintain recovery information beyond local recovery mechanisms.
    • The coordinator uses a two-phase commit protocol to ensure atomicity.

    Recovery Facilities

    • Database Management Systems (DBMS) use facilities for recovery:
    • Backup mechanisms create periodic backups.
    • A logging facility tracks the current status of transactions.
    • The Checkpoint facility enables updates (in progress) to become permanent.
    • The Recovery manager restores the database to a consistent state.

    Log File

    • Stores information about database updates.
    • Contains records of transactions.
    • Contains checkpoint records.
    • Often used for additional purposes like audits.

    Transaction and Recovery

    • Transactions are basic recovery units.
    • The recovery manager is responsible for ensuring atomicity and durability.
    • If the failure occurs between commit and writing to stable storage, the recovery manager must redo the transaction's updates.
    • If a transaction is not committed at the time of failure, its effects need to be undone.

    Recovery Techniques

    • Database damage can be physical or result in state inconsistency following failure.
    • Recovery mechanisms differ based on the type of damage.
    • If the database is damaged, a restore of the last usable backup and reapplication of committed transactions using the log file is required.
    • With extensive damage (catastrophic failure, like physical media failure), a backup copy, re-executed committed transactions from the log up to the point of failure, may be used.
    • If the inconsistency is not a result of physical damage, reversing changes with the transaction log, undoing inconsistent changes, and potentially redoing some transactions to ensure updates reach secondary storage.

    Checkpointing

    • A checkpoint is a synchronization point between the database and the log file.
    • All buffers are written to secondary storage.
    • A checkpoint record is generated with identifiers of active transactions
    • After a failure, all transactions that committed after the checkpoint are redone. Active transactions at the time of the crash are undone.

    Immediate Update/Update-In-Place

    • Updates are applied to the database as they occur.
    • Redo of committed transactions and undo of non-committed transactions are necessary after the failure.
    • Log records have to be written before writing to the database. (write-ahead log protocol)
    • A transaction active at the time of failure must be undone.
    • Undo operations are performed in reverse order.

    Principles of ARIES Recovery Algorithm

    • Write-ahead logging ensures a log record is written to stable storage before a database update.
    • Redo operation retraces prior actions to restore the database to its status at the time of a crash.
    • Undo operations, which deal with uncommitted transactions, are logged to prevent repetition of the operations.

    ARIES Concepts

    • ARIES maintains two data structures and extends log records:
      • Transaction table tracks active (started but not committed/aborted) transactions.
      • Dirty page table lists pages modified but not yet written to disk.

    Recovery in Multidatabase Systems

    • Transaction that accesses multiple databases is a multidatabase transaction.
    • Databases may be of differing types.
    • Each DBMS in a multidatabase transaction uses its own local recovery mechanism.
    • A two-level recovery mechanism using a global recovery manager (coordinator) is crucial to maintain atomicity in multidatabase transactions.
    • The two-phase commit protocol ensures the required information and effects are written to (or from) the log.

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    Related Documents

    Chapter Four: Database Recovery Techniques PDF

    Description

    Test your knowledge on database recovery, types of failures, and the characteristics of stable storage. This quiz covers essential concepts related to ensuring data consistency and dealing with system failures in databases.

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