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Which of the following describes the concept of interleaving in transaction processing?

  • Executing multiple transactions concurrently, potentially leading to inconsistencies (correct)
  • Executing multiple transactions sequentially without overlap
  • Creating a backup for each transaction before execution
  • Locking resources to prevent concurrent access

What is the purpose of a lock manager in database systems?

  • To back up the database to avoid data loss
  • To assign and manage locks for resource control (correct)
  • To enforce data consistency across multiple databases
  • To optimize the database queries for faster execution

Which of the following is NOT one of the ACID properties of a transaction?

  • Atomicity
  • Durability
  • Isolation
  • Concurrency (correct)

What is a deadlock in transaction processing?

<p>When transactions are unable to proceed because each is waiting for the other to release a resource (B)</p> Signup and view all the answers

Which locking mechanism allows different transactions to access different columns of the same row simultaneously?

<p>Field-level lock (D)</p> Signup and view all the answers

What is an optimistic method in transaction processing primarily focused on?

<p>Minimizing the use of locks during transaction execution (C)</p> Signup and view all the answers

Which of the following statements best describes serializable schedules?

<p>Schedules that produce the same result as executing transactions sequentially (B)</p> Signup and view all the answers

What is one method to prevent deadlocks in a database system?

<p>Implementing a timeout for transactions (A)</p> Signup and view all the answers

What is the primary benefit of interleaving transactions?

<p>It can potentially improve system performance. (B)</p> Signup and view all the answers

Which statement accurately describes a serial schedule?

<p>It processes transactions sequentially without overlapping. (B)</p> Signup and view all the answers

In the context of ACID properties, what does 'durability' refer to?

<p>Guaranteeing that once a transaction is committed, it will remain so even in the event of a failure. (B)</p> Signup and view all the answers

What is a key feature of cache matching algorithms?

<p>They group same reads from different threads together to optimize performance. (B)</p> Signup and view all the answers

What happens to a database when transactions are incorrectly scheduled?

<p>It may become inconsistent. (C)</p> Signup and view all the answers

Which of the following best defines the property of atomicity in transactions?

<p>Transactions must either complete entirely or not at all. (A)</p> Signup and view all the answers

What distinguishes a serializable schedule from an equivalent schedule?

<p>It yields the same output as some serial schedules. (B)</p> Signup and view all the answers

What is the result of interleaving transactions in a manner that is considered 'bad'?

<p>Inconsistent transaction results leading to potential data loss. (A)</p> Signup and view all the answers

What is the primary responsibility of the application-level code in relation to database transactions?

<p>Preserve the consistency of the database (A)</p> Signup and view all the answers

Which ACID property ensures that once a transaction is completed, the changes will survive system crashes?

<p>Durability (D)</p> Signup and view all the answers

In the event of a failure during a transaction, what mechanism allows the transaction to return to a previously defined state?

<p>SAVEPOINT (A)</p> Signup and view all the answers

Why is it important to log transaction details on disk rather than in memory?

<p>Disk logging guarantees data permanence after a crash (D)</p> Signup and view all the answers

Which of the following ensures that transactions are executed as if they are isolated from one another?

<p>Isolation (B)</p> Signup and view all the answers

What occurs if a transaction fails to complete its operations during execution?

<p>The system state may remain inconsistent (A)</p> Signup and view all the answers

What SQL command would be used to discard all pending changes during a transaction?

<p>ROLLBACK (D)</p> Signup and view all the answers

What is the effect of issuing a COMMIT command after a transaction?

<p>It makes all pending changes permanent (D)</p> Signup and view all the answers

Flashcards

Interleaving

Allowing operations from different transactions to execute in an unpredictable order.

Serial Schedule

A schedule where transactions execute one after another without any interleaving.

Equivalent Schedule

Two schedules that produce the same final state.

Serializable Schedule

A schedule where the final result is the same as if transactions had executed serially in some order.

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Atomicity

All operations within a transaction must complete successfully, or none of them do.

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Consistency

Database rules are followed throughout the transaction.

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Isolation

Transactions execute independently, without interference from other transactions.

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Durability

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

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Data Damage

When the actual data stored in the database is corrupted or lost, often due to physical media failure.

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Transaction Log Damage

When the record of changes made by transactions is corrupted or lost, making it impossible to recover the correct state of the database.

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Concurrency Control

A mechanism to manage simultaneous access to the database by multiple users or processes, ensuring data consistency and integrity.

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Lock

A mechanism used in concurrency control to restrict access to data by other transactions, ensuring that only one transaction can modify the data at a time.

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Lock Granularity

The level of detail at which data is locked, ranging from locking the entire database to individual rows or even fields.

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Deadlock

A situation where two or more transactions are waiting for each other to release resources, resulting in a standstill.

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Optimistic Method

A concurrency control approach that assumes conflicts are rare and allows transactions to proceed without locking, verifying data consistency later and rolling back if necessary.

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3-Phase Method

A popular optimistic concurrency control method that involves reading, validating, and writing data in separate phases, ensuring consistency before committing changes.

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Transaction Consistency

Ensures that a transaction maintains the database's integrity and leaves it in a valid state, even if the transaction is interrupted.

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Transaction Isolation

Guarantees that concurrent transactions execute independently, preventing interference and ensuring that results are not affected by other concurrent transactions.

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Transaction Durability

Ensures that once a transaction is committed, its changes are permanently stored in the database and survive system crashes or failures.

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Transaction Log

A record that keeps track of all transaction details, including changes made to the database, completion times, and methods used.

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COMMIT

Ends the current transaction and makes all pending changes permanent in the database.

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ROLLBACK

Discards all pending changes made within a transaction, effectively undoing any modifications.

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SAVEPOINT

A marker within a transaction that allows part of the transaction to be committed or rolled back independently.

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ROLLBACK TO SAVEPOINT

Reverts the transaction back to a specified SAVEPOINT, undoing only the changes made after that point.

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Study Notes

INF2003: Database Systems - Transaction

  • Transaction Definition: A program that reads and writes data (abbreviated as TXN). In SQL, a transaction is a series of SELECT, UPDATE, and INSERT statements.
  • Transaction Example: Transferring 100 dollars from one account to another. This would involve reading the balance, updating the balance, and writing the new balance.
  • Concurrency Issue: Multiple users accessing and modifying the same data simultaneously can lead to inconsistent results. Each user can start a transaction independently, and different transactions can access the same data, making the order of operations crucial.
  • Concurrency Example (TXN-1 & TXN-2): Illustrates how different transaction execution orders can lead to different outcomes like 106 dollars more for one account and 3 dollars less for another.
  • Interleaving: Arbitrary ordering of operations within transactions can lead to unexpected outcomes, such as inconsistencies in the database. Interleaving can make the final results unexpectedly different.

2nd Half Topics

  • W8: Indexing (mainly centralized)
  • W9: Transactions and Concurrency
  • W10: NoSQL
  • W11: Blockchain
  • W12: Data Warehouse

Transaction Properties (ACID)

  • Atomicity: All operations within a transaction must be successful, or none of them will be applied. If an operation fails, the entire transaction is aborted. Conceptual point that all happens or nothing happens.
  • Consistency: A transaction ensures that the database remains in a valid state after execution.
  • Isolation: Transactions are isolated from one another, meaning that the intermediate steps of one transaction are not visible to other concurrent transactions (as if they are happening in isolation).
  • Durability: Once a transaction is committed, the changes made to the database are permanent and cannot be lost even if the system fails.

ACID: Consistency and Isolation

  • Consistency: Before and after a transaction, the database must be in a valid state.
  • Isolation: Ensures that concurrent transactions execute as if they are running serially. The application-level software is responsible for ensuring that transactions are consistent.
  • Concurrency Control: Locks are used to manage concurrent access to database resources, preventing inconsistent data.

ACID: Durability

  • Durability: Ensures data integrity and persistence, even after system failures. A transaction's changes become permanent, even if the system itself crashes.

Transactions in SQL

  • COMMIT: Permanently saves all changes made during the transaction.
  • ROLLBACK: Reverses all changes made during the transaction if something goes wrong.
  • SAVEPOINT: Allows for partial rollback, saving a specific point within a transaction that can later be rolled back to.

Recovery

  • Transaction Failures: Various situations, like system crashes, power outages, or user mistakes, can interrupt transactions.
  • Data Recovery: Critical to ensure that the data is recoverable by various means, by backups, recovery tools, previous checkpoints/logs.

Concurrency Control: Locking

  • Granularity: Different levels of locking (database, table, page, row, field). Higher-level locks (db and table level) are generally not used as they are not very practical in concurrent systems.
  • Locking Methods: Techniques to prevent data inconsistency.
  • Deadlocks: Situations where two or more transactions are waiting indefinitely for each other to release locks.

Lock and Optimistic Methods

  • Deadlock Prevention: Techniques for preventing deadlock situations, such as timeouts on locks, and proper programming.
  • Optimistic Locking: Avoiding strict locks. Transaction runs by assuming no conflicts, then verifies if changes have occurred since the start in a 3-phase method.

Summary

  • Transaction Importance: Critical for maintaining data consistency in large-scale database systems.
  • ACID Properties: Fundamental to reliable database transaction management.
  • Concurrency Control: Essential for handling multiple simultaneous transactions.
  • Recovery Procedures: Need robust procedures in case of crashes.

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Related Documents

INF2003 Database Systems Transaction AY24/25 PDF

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