Unit V: Database Transaction Management
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What indicates that the system is in a deadlock state?

  • A single transaction is waiting for a lock.
  • The resources are assigned in a circular manner.
  • All transactions are executing without waiting.
  • The wait-for graph has at least one cycle. (correct)

What is the primary criterion for selecting a transaction to roll back in a deadlock situation?

  • The transaction that is the oldest in the deadlock set.
  • The transaction that holds the highest number of locks.
  • The transaction that completed first.
  • The transaction that has incurred the least cost. (correct)

Which action is NOT part of the rollback process when resolving a deadlock?

  • Restarting the transaction immediately after rollback. (correct)
  • Determining how far the transaction needs to roll back.
  • Aborting the victim transaction completely.
  • Rolling back only as far as necessary to release specific locks.

What can happen if the oldest transaction in the deadlock set is consistently not chosen as a victim?

<p>It may cause starvation for that transaction. (C)</p> Signup and view all the answers

Which type of transaction failure requires the database system to terminate an active transaction?

<p>System errors caused by deadlock. (C)</p> Signup and view all the answers

What is the main purpose of concurrency control protocols?

<p>To ensure that concurrent schedules are conflict/view serializable and recoverable (A)</p> Signup and view all the answers

Which lock mode allows both reading and writing of a data item?

<p>Exclusive (X) mode (B)</p> Signup and view all the answers

What must happen when a transaction requests a lock?

<p>The transaction can only proceed after the lock request is granted (B)</p> Signup and view all the answers

What happens if a transaction holds an exclusive lock on a data item?

<p>No other transaction may hold any lock on that data item (D)</p> Signup and view all the answers

What situation is referred to when two transactions are waiting on each other to release their locks?

<p>Deadlock (C)</p> Signup and view all the answers

If starvation occurs during the locking protocol, what is likely happening?

<p>A transaction is being prioritized over others indefinitely (B)</p> Signup and view all the answers

How do locking protocols maintain serializability?

<p>By imposing rules on requesting and releasing locks to restrict possible schedules (D)</p> Signup and view all the answers

What is the consequence of a transaction that has been aborted?

<p>The state of the database is restored to what it was prior to the start. (B)</p> Signup and view all the answers

What does a lock-compatibility matrix define?

<p>Which types of locks can be held simultaneously on a data item (A)</p> Signup and view all the answers

What is a primary advantage of allowing multiple transactions to run concurrently?

<p>It leads to increased processor and disk utilization. (B)</p> Signup and view all the answers

What defines a schedule in the context of concurrent transactions?

<p>The chronological order in which instructions of concurrent transactions are executed. (C)</p> Signup and view all the answers

What must be preserved in a schedule for concurrent transactions?

<p>The order of instructions in each individual transaction. (C)</p> Signup and view all the answers

What happens to a transaction that completes successfully?

<p>It has a commit instruction as its last statement. (D)</p> Signup and view all the answers

In the context of schedules, what does serializability imply?

<p>The sequence of transactions does not affect the final state of the database. (D)</p> Signup and view all the answers

What is a notable advantage of the tree protocol over two-phase locking?

<p>It allows schedules that are not possible under two-phase locking. (C)</p> Signup and view all the answers

Which of the following is a possible action after a transaction has been aborted?

<p>Restart the transaction only if no internal logical error exists. (B)</p> Signup and view all the answers

Which of the following is a drawback of the protocol mentioned?

<p>Transactions may need to lock data they don't access. (B)</p> Signup and view all the answers

Which schedule preserves the sum of accounts A and B?

<p>A serial schedule where T2 is executed before T1. (A), A serial schedule where T1 is executed before T2. (B)</p> Signup and view all the answers

In the wait-die scheme, what happens to younger transactions waiting for older ones?

<p>They are rolled back instead of waiting. (D)</p> Signup and view all the answers

What is the primary role of a transaction in a database system?

<p>To perform program execution that may access and update data items (A)</p> Signup and view all the answers

What is the primary function of deadlock prevention protocols?

<p>To prevent the system from ever entering a deadlock state. (B)</p> Signup and view all the answers

Which of the following describes the atomicity requirement in transaction management?

<p>All parts of a transaction must be completed successfully or none at all (B)</p> Signup and view all the answers

What defines a system as being deadlocked?

<p>All transaction are waiting for resources that are being held by other transactions. (D)</p> Signup and view all the answers

What can lead to an inconsistent database state during a transaction?

<p>Completing a transaction with partial updates (B)</p> Signup and view all the answers

Which method requires transactions to lock all required data items before execution?

<p>Graph-based protocol. (C)</p> Signup and view all the answers

What does the durability requirement in transaction management ensure?

<p>Updates will not be lost even in case of a failure (A)</p> Signup and view all the answers

What are the main issues to address in the context of database transactions?

<p>Failures and concurrent execution of transactions (D)</p> Signup and view all the answers

What is a limitation of timeout-based deadlock handling schemes?

<p>Difficulty in setting an appropriate timeout value. (B)</p> Signup and view all the answers

What does the term 'cascaded aborts' refer to in transaction management?

<p>The situation where one transaction's failure causes a chain reaction of aborts in others (A)</p> Signup and view all the answers

What does the wait-for graph represent in deadlock detection?

<p>The relationships among active transactions. (C)</p> Signup and view all the answers

Which of the following best describes a recoverable schedule?

<p>A schedule where transactions can only be committed after all previous transactions have completed (D)</p> Signup and view all the answers

Which method is commonly used for handling deadlocks in database systems?

<p>Lock-based protocols (B)</p> Signup and view all the answers

What is the primary function of the Two-Phase Locking Protocol?

<p>To ensure conflict-serializable schedules (D)</p> Signup and view all the answers

In the Two-Phase Locking Protocol, what happens during the Shrinking Phase?

<p>Transactions may release locks but cannot obtain new ones (B)</p> Signup and view all the answers

Which type of two-phase locking ensures that all exclusive locks are held until a transaction commits or aborts?

<p>Rigorous two-phase locking (D)</p> Signup and view all the answers

Which of the following statements is true about two-phase locking?

<p>It does not ensure freedom from deadlocks (A)</p> Signup and view all the answers

What is the primary drawback of basic two-phase locking?

<p>It can cause a higher incidence of starvation (A)</p> Signup and view all the answers

Which of the following describes the condition under which two-phase locking is necessary for conflict serializability?

<p>In the absence of additional information about data access ordering (B)</p> Signup and view all the answers

What major issue can occur when using the Two-Phase Locking Protocol without any extensions?

<p>It can lead to the occurrence of cascading roll-backs (B)</p> Signup and view all the answers

What guarantees does rigorous two-phase locking provide compared to basic two-phase locking?

<p>It ensures all locks are held until a transaction either commits or aborts (B)</p> Signup and view all the answers

Flashcards

Database Transaction

A unit of program execution that accesses and modifies data in a database.

ACID Properties

Atomicity, Consistency, Isolation, Durability - properties that guarantee the reliability of database transactions.

Atomicity

All parts of a transaction must be treated as a single, indivisible unit.

Consistency

Transaction must preserve the database’s integrity constraints.

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Isolation

Transactions should execute concurrently without interfering with each other.

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Durability

Once a transaction is committed, its changes are permanently saved.

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Fund Transfer Example

Illustrates a transaction that transfers money between accounts.

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Concurrency Control

Mechanisms to manage multiple concurrent transactions effectively.

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Transaction States

Different stages a transaction can go through: failed, aborted, committed

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Concurrent Executions

Multiple transactions running simultaneously to improve system efficiency

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Schedule

Order of instructions for concurrent transactions, respecting individual order

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Serial Schedule

Transaction execution order maintains database consistency.

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Concurrency Control

Mechanisms that ensure concurrent transactions don't conflict.

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Transaction Abort

Transaction is cancelled due to errors, rolling back to previous state

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Transaction Commit

Transaction successfully executed and permanently saved to database

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Serializability

A schedule that preserves database consistency even in concurrent executions.

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Serializability Tests

Tests used to ensure concurrent schedules in database systems are viewed as a single sequential execution

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Lock-Based Protocols

Concurrency control methods using locks to manage access to data items in database systems

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Exclusive (X) Lock

A lock mode permitting both reading and writing of a data item

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Shared (S) Lock

A lock mode allowing only reading of a data item

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Lock Compatibility

A set of rules determining if two locks on a data item are compatible in a concurrent database system.

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Deadlock

A situation in a concurrent system where two or more transactions are blocked indefinitely, waiting for each other to release resources.

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Concurrency Control Manager

The component of a database system responsible for managing concurrent access to shared resources, including enforcing database consistency.

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Locking Protocols

Sets of rules for transactions to follow while acquiring and releasing locks in a database system.

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Two-Phase Locking Protocol

A protocol that ensures transaction schedules are conflict-serializable.

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Strict two-phase locking

Transaction must hold all exclusive locks until commit/abort, guaranteeing recoverability and avoiding cascading roll-backs.

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Rigorous two-phase locking

Transaction must hold all locks until commit/abort, enabling serializing transactions based on commit order.

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Deadlocks

A situation where two or more transactions are blocked indefinitely, preventing any of them from proceeding.

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Concurrency control manager

A system component responsible for preventing starvation and managing concurrent transactions.

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Conflict serializability

A schedule of concurrent transactions that yields the same results as some serial execution.

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Two-phase locking not necessary

There exist conflict-serializable schedules that cannot be produced by the two-phase locking protocol.

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Lock points

The specific point in a transaction where it acquires its final lock.

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Deadlock Handling

Techniques to prevent or resolve situations where transactions are blocked indefinitely, waiting for each other to release resources.

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Deadlock Prevention

Strategies to ensure a system never enters a deadlock state by controlling resource acquisition orders.

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Wait-Die Scheme

A deadlock prevention technique where older transactions can wait for younger ones, but younger transactions are aborted if they request resources held by older ones.

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Wound-Wait Scheme

A deadlock prevention technique where an older transaction aborts a younger transaction instead of waiting for it to release a resource.

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Timeout-Based Scheme

A technique that sets a time limit for a transaction to acquire a resource. If the resource isn't acquired within the limit, the transaction is aborted.

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Wait-for Graph

A graphical representation of dependencies among transactions, where edges show which transaction is waiting for another.

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Tree Protocol

A deadlock-free protocol for transactions that leverages a hierarchical structure to order resource requests.

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Deadlock state

A situation where a set of transactions are blocked indefinitely, as each transaction awaits a resource held by another transaction in the set.

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Deadlock Detection

A system checks for cycles in a wait-for graph to identify deadlocks.

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Deadlock Recovery

Selecting a transaction to rollback (the victim) to break a deadlock cycle, minimizing the cost of rollback.

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Transaction Failure (Logical)

A transaction fails due to an internal error, thus unable to complete.

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System Crash

A database failure, often due to hardware faults, that interrupts ongoing activities.

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Partial Rollback

Rolling back a transaction only to the point where it releases locks needed by another transaction in a cycle.

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Study Notes

Unit V: Database Transaction Management

  • Unit V covers Database Transaction Management, including foundational concepts like transactions, transaction states, ACID properties, scheduling, concurrency control (lock-based, time-stamp based, deadlock handling), recovery methods (shadow-paging, log-based recovery, checkpoints), and database modifications.
  • A transaction is a unit of program execution that accesses and updates data. A common example is transferring money between accounts.
  • Key issues are failures (hardware, system crashes) and concurrent execution of multiple transactions.
  • ACID properties ensure reliable transactions:
    • Atomicity: All operations succeed or none do. If a part fails, the whole transaction is rolled back.
    • Consistency: A transaction leaves the database in a valid state.
    • Isolation: Concurrent transactions don't interfere with each other.
    • Durability: Once committed, changes are permanent, even after failures.
  • Transaction states include active, partially committed, failed, aborted, and committed states.
  • Schedules specify the order of instructions in concurrent transactions. Serial schedules execute transactions one after another. Non-serial schedules execute simultaneously.
  • Serializability ensures that a schedule yields the same outcome as a serial execution.
  • Conflict serializability: A schedule is conflict serializable if it can be converted to a serial schedule by swapping non-conflicting operations.
  • View serializability: A schedule is view serializable if every transaction's view of data is the same regardless of whether it is executed concurrently or in isolation.
  • Recoverable schedules ensure that if a transaction reads data from another transaction, that other transaction should have already committed.
  • Cascading rollbacks: If one transaction aborts, related transactions may also need to abort, causing cascading effects. Cascadeless schedules avoid this problem.
  • Concurrency control schemes manage concurrent transactions to prevent conflicts and maintain consistency.
  • Locking protocols control concurrent access with locks (X-exclusive, S-shared) to data items.
  • Deadlocks occur when transactions wait indefinitely for each other's locks. Detection and recovery strategies are crucial.
  • Starvation can happen if a transaction is repeatedly delayed or blocked indefinitely from accessing resources.
  • The two-phase locking protocol (2PL) is a common concurrency control mechanism, with growing and shrinking phases, ensuring atomicity.
  • Extensions to 2PL such as strict or rigorous two-phase locking address recoverability and avoid cascading effects.
  • Log-based recovery uses a log to record transaction operations (writes and reads) to rebuild the consistent state of the database after failures.
  • Immediate vs. deferred modification approaches describe when updates are made to disk storage and when they're written to the log.
  • Recovery techniques like shadow-paging, which maintains copies of data, and checkpoints, which periodically record the state of the system.

Other Important Concepts

  • Different strategies for deadlock prevention and handling.
  • Wait-die and wound-wait schemes.
  • Timeout-based schemes.
  • Wait-for graphs.
  • Recovery systems: methods for restoring a database to a consistent state after failures
  • Understanding the ACID properties of transactions.
  • Knowledge of failure modes (transaction and system failures).
  • Awareness of relevant graph algorithms (such as cycle detection).

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Related Documents

Unit V Database Transaction Management PDF

Description

This quiz covers key concepts in Database Transaction Management, including the ACID properties that ensure reliable transactions, various scheduling techniques, and recovery methods. Additionally, it explores issues like concurrency control and transaction states essential for maintaining data integrity and consistency.

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