Database Deadlocks and Concurrency Control
37 Questions
5 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is a disadvantage of using time stamping methods in concurrency control?

  • Decreases database resource demand
  • Increases processing overhead (correct)
  • Requires only one additional stamp field
  • Reduces memory needs

    • In the Wait/Die scheme, what happens to an older transaction if it cannot get the required locks?

  • It dies and is rescheduled (correct)
  • It continues with its operations
  • It is immediately canceled
  • It forces the younger transaction to release the locks

    • What is a key feature of the Wound/Wait scheme?

  • All transactions are allowed to access the locks simultaneously
  • Older transactions must wait for the younger ones to complete
  • Older transactions can request locks and preempt younger transactions (correct)
  • Younger transactions can preempt older transactions

    • What impact do time stamping methods have on a database’s memory requirements?

    <p>They require more memory due to additional fields</p> Signup and view all the answers

    Which of the following accurately describes the Wait/Die strategy?

    <p>Younger transactions are rolled back if older transactions cannot obtain locks</p> Signup and view all the answers

    What causes a deadlock in transaction management?

    <p>When two transactions wait indefinitely for each other to unlock data.</p> Signup and view all the answers

    Which term is commonly used to refer to a deadlock?

    <p>Deadly embrace</p> Signup and view all the answers

    Which method is NOT a control technique for managing deadlocks?

    <p>Deadlock termination</p> Signup and view all the answers

    What is the primary function of time stamping in transaction management?

    <p>To assign a unique global time stamp to ensure order.</p> Signup and view all the answers

    Which property of time stamping ensures that no two transactions have the same time stamp value?

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

    Under which condition would deadlock control methods be selected?

    <p>Depending on the database environment.</p> Signup and view all the answers

    Which time stamping property ensures that the values always increase over time?

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

    What can be considered a classification of deadlock control methods?

    <p>Prevention, detection, and avoidance</p> Signup and view all the answers

    What does atomicity ensure in a transaction?

    <p>All operations of a transaction must be completed or none at all.</p> Signup and view all the answers

    Which property guarantees that once transactions are committed, they cannot be undone?

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

    What is the consequence of an improper or incomplete transaction?

    <p>It can corrupt the database integrity.</p> Signup and view all the answers

    Which of the following provides consistency in a database?

    <p>Database remains in a consistent state after transactions.</p> Signup and view all the answers

    What does the isolation property of transactions imply?

    <p>Transactions can run without interferences from others.</p> Signup and view all the answers

    Which property ensures consistent results from concurrent transactions?

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

    How can users define constraints in a database?

    <p>Through enforceable business rules.</p> Signup and view all the answers

    What is not a characteristic of transactions in a database?

    <p>Transactions must be reversible in all cases.</p> Signup and view all the answers

    What is the first phase in optimistic concurrency control?

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

    What is the purpose of the validation phase in optimistic concurrency control?

    <p>To ensure changes do not affect database integrity</p> Signup and view all the answers

    Which transaction isolation level allows reading uncommitted data?

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

    What characterizes a nonrepeatable read?

    <p>Reading a row and getting different results from the same query</p> Signup and view all the answers

    During which phase are changes applied permanently to the database?

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

    What does the term 'phantom read' refer to?

    <p>Executing a query and encountering new matching rows later</p> Signup and view all the answers

    How are transaction isolation levels defined?

    <p>By the type of 'reads' allowed</p> Signup and view all the answers

    Which of the following is NOT a phase in optimistic concurrency control?

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

    What happens if a transaction was committed before the last check point?

    <p>Nothing needs to be done.</p> Signup and view all the answers

    What is the purpose of ROLLBACK in a transaction?

    <p>To restore the database to a previous state.</p> Signup and view all the answers

    Which property ensures that transactions are completed fully or not at all?

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

    In the context of database transactions, what does a lock provide?

    <p>Unique access to a data item by one transaction.</p> Signup and view all the answers

    What is the role of the transaction log in recovery?

    <p>It helps to redo or rollback transactions after a failure.</p> Signup and view all the answers

    What does the two-phase locking protocol guarantee?

    <p>Serializability of transaction schedules.</p> Signup and view all the answers

    Which of the following is NOT a property of transactions?

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

    What must happen if a transaction had a ROLLBACK operation after the last check point?

    <p>The DBMS uses the transaction log to undo operations.</p> Signup and view all the answers

    Study Notes

    Deadlocks

    • Occur when two transactions wait indefinitely for each other to unlock data
    • Also known as deadly embrace
    • Control techniques include deadlock prevention, deadlock detection, and deadlock avoidance
    • Choice of deadlock control method depends on the database environment

    Concurrency Control With Time Stamping Methods

    • Assigns a global, unique time stamp to each transaction
    • Produces an explicit order in which transactions are submitted to the DBMS
    • Properties include uniqueness (no equal time stamps) and monotonicity (time stamp values always increase)
    • Disadvantages include:
      • Two additional timestamp fields needed for each value stored
      • Increased memory needs
      • Increased processing overhead
      • Demands many system resources

    Wait/Die and Wound/Wait Schemes

    • Wait/Die: an older transaction waits for a younger transaction to finish before requesting locks. If not, the newer transaction is rescheduled.
    • Wound/Wait: an older transaction can request the lock, preempt the younger transaction, and reschedule it. If not, the younger transaction waits.

    Concurrency Control with Optimistic Methods

    • Concurrency control approach assumes that conflicts between transactions are rare
    • Read Phase:
      • Transaction reads database
      • Executes computations
      • Updates private copy of database values
    • Validation Phase:
      • Transaction validated to ensure changes do not affect database integrity or consistency
    • Write Phase:
      • Changes permanently applied to the database

    ANSI Levels of Transaction Isolation

    • Defines transaction management based on transaction isolation levels
    • Isolation levels denote the degree to which transaction data is protected from other concurrent transactions
    • Described by the type of "reads" a transaction allows or not
    • Types of "reads":
      • Dirty Read: transaction reads data not yet committed
      • Nonrepeatable Read: transaction reads a row at time t1 and then at time t2 gets different results (original row may have been updated or deleted)
      • Phantom Read: transaction executes a query at time t1 then at time t2 gets additional rows that satisfy the query

    Transaction Recovery

    • Recovery process steps:
      • Identify the last checkpoint in the transaction log
      • If committed before the checkpoint, no action needed
      • If committed after the checkpoint, the transaction log is used to redo the transaction
      • If a ROLLBACK occurred after the last checkpoint, the DBMS uses the transaction log records to ROLLBACK or undo the operations by using the “before” values in the transaction log

    Summary

    • A transaction is a sequence of database operations that access the database
    • Transactions have four primary properties: atomicity, consistency, isolation, and durability
    • SQL supports transactions using COMMIT (saving changes to disk) and ROLLBACK (restoring the previous database state)
    • Concurrency control manages the simultaneous execution of transactions
    • A lock guarantees unique access to a data item by a transaction
    • Serializability is guaranteed through two-phase locking

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    Chp10.pdf

    Description

    Explore the concepts of deadlocks, concurrency control methods, and their impact on database management systems. This quiz covers techniques like wait/die and wound/wait schemes, as well as timestamping methods. Test your understanding of how these mechanisms help manage simultaneous transactions effectively.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser