Database Management Systems Chapter 18 Part 2
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Questions and Answers

What is the primary purpose of Strict Two-phase Locking (Strict 2PL) protocol in transaction management?

  • To ensure that all transactions are executed in a serializable manner (correct)
  • To allow concurrent transactions without restrictions
  • To facilitate faster read operations
  • To minimize memory usage during transaction execution

    • What must happen if a transaction Ti is aborted?

  • Only the last action performed by Ti must be undone
  • All actions of Ti must be undone and any transaction reading from Ti must also be aborted (correct)
  • All its actions are final and cannot be undone
  • Ti's locks are released immediately after aborting

    • During which phase of the Aries recovery algorithm are dirty pages updated in the buffer pool?

  • Commit Phase
  • Redo Phase (correct)
  • Analysis Phase
  • Undo Phase

    • What triggers the release of a transaction's locks in a DBMS according to the content?

    <p>At the time of transaction completion only if committed</p> Signup and view all the answers

    Why is it essential to write log records to disk before the changed page in transaction management?

    <p>To maintain a proper order of operations for recovering from crashes</p> Signup and view all the answers

    Study Notes

    Transaction Management Overview

    • Anomalies can occur during interleaved execution, particularly with uncommitted data.
    • Types of conflicts include Overwriting Uncommitted Data, often represented as WW Conflicts.

    Lock-Based Concurrency Control

    • Strict Two-phase Locking Protocol (Strict 2PL):
      • Requires obtaining a shared (S) lock before reading and an exclusive (X) lock before writing.
      • Locks are released only when the transaction completes.
      • No other transaction can obtain any lock on an object held under an exclusive lock.
      • Ensures only serializable schedules.

    Aborting a Transaction

    • When a transaction (Ti) is aborted, all its changes must be undone.
    • If another transaction (Tj) reads data last written by Ti, Tj also must be aborted to maintain consistency.
    • Systems typically prevent cascading aborts by keeping locks until a transaction commits.
    • Transactions can only read data written by another transaction after the latter commits.

    Logging Mechanism

    • A log records every write action of a transaction to facilitate rollback and system recovery.
    • Log entries for writes include both the old and new values.
    • Commit and abort actions of transactions are also recorded in the log.
    • Log records must first be written to disk before changes to the actual data.

    Log Structure and Recovery

    • Log records are linked by transaction IDs, simplifying the undo process.
    • Logs are often duplicated and stored in stable storage for reliability.
    • Aries Recovery Algorithm Phases:
      • Analysis Phase: Scans the log from the last checkpoint to identify active transactions and dirty pages.
      • Redo Phase: Reapplies updates to dirty pages in the buffer pool to ensure data consistency.

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    lect(7) Transaction Management (2).pptx

    Description

    Explore the intricacies of transaction management in Database Management Systems with a focus on anomalies that occur from interleaved execution. This quiz covers concepts such as overwriting uncommitted data and the strict two-phase locking protocol. Test your understanding of these critical mechanisms in ensuring data consistency and integrity.

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