Concurrency Control in DBMS: Ensuring Serializability of Transactions Quiz and Flashcards

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Questions and Answers

What does a transaction aim to achieve?

Delete data from the database

Change the database state to an inconsistent state

Interrupt other transactions

Change the database state to another consistent state (correct)

Which property of a transaction ensures that all data should be entered or failed in one transaction?

Isolation

Consistency

Atomicity (correct)

Durability

What is the primary purpose of concurrency control?

Allow multiple transactions to interfere with each other

Speed up the processing of transactions

Ensure data is always inconsistent

Maintain data integrity and consistency (correct)

What problems can occur without proper concurrency control mechanisms in place?

Data inconsistency and integrity issues Signup and view all the answers

Which property of a transaction ensures that the persistence of a successful transaction should be guaranteed?

Durability Signup and view all the answers

What is the purpose of maintaining isolation between transactions?

To prevent other transactions from affecting an ongoing transaction Signup and view all the answers

What is the main purpose of lock-based protocols in DBMS?

To eliminate concurrency problems by locking a transaction to a single user Signup and view all the answers

Which type of variable is a lock in DBMS?

Data variable Signup and view all the answers

What does the timestamp-based protocol use to serialize the execution of concurrent transactions?

System time or logical counter Signup and view all the answers

In the timestamp-based technique, what determines the priority of conflicting transactions?

Time of execution Signup and view all the answers

What do locks in DBMS help synchronize?

Access to the database items by concurrent transactions Signup and view all the answers

Why is concurrency control important in a Database Management System (DBMS)?

To ensure data integrity and consistency Signup and view all the answers

What is the main purpose of concurrency control in a database system?

To guarantee data integrity and consistency Signup and view all the answers

Which problem arises when transactions update the same data simultaneously?

Lost insert Signup and view all the answers

What is the purpose of creating a serializable schedule in a database system?

To guarantee the possibility of transaction serialization Signup and view all the answers

Which issue occurs when other transactions refer to the intermediate result of a transaction?

Dirty read Signup and view all the answers

When does an unrepeatable read problem occur in a database system?

When a transaction executes the same query twice with different results Signup and view all the answers

Why is ensuring data integrity and consistency important in a database system?

To avoid inconsistency and maintain reliable data Signup and view all the answers

Study Notes

Concurrency Control Techniques

There are four concurrency control techniques: lock-based, timestamp-based, multi-version, and verification (optimistic) based.

Lock-Based Technique

Lock-based protocols eliminate concurrency problems in DBMS by locking or isolating a particular transaction to a single user.
A lock is a data variable associated with a data item, signifying the operations that can be performed on the data item.
Locks help synchronize access to database items by concurrent transactions.
All lock requests are made to the concurrency-control manager, and transactions proceed only once the lock request is granted.

Timestamp-Based Technique

Timestamp-based protocol uses system time or logical counter as a timestamp to serialize the execution of concurrent transactions.
The protocol ensures that every conflicting read and write operations are executed in a timestamp order.
The older transaction is always given priority in this method, which uses system time to determine the time stamp of the transaction.

Definition and Purpose of Concurrency Control

Concurrency control is a function that enables the successful execution of several transactions at the same time in a database system that supports a multi-user environment.
The purpose of concurrency control is to create a serializable schedule, ensure the possibility of transaction serialization, guarantee the maximum sharing level, minimum response time, and maximum system activity, and ensure data integrity and consistency.

Problems that Occur when Concurrency is Not Controlled

Lost update: occurs when transactions update the same data simultaneously, and the later transaction overwrites the update value before the previous transaction has completed.
Dirty read: other transactions refer to the intermediate execution result of a transaction.
Inconsistency: a database remains inconsistent when two transactions are executed at the same time.
Cascading rollback: when a specific transaction cancels processing, if data is shared by multiple transactions, the part processed by other transactions cannot be cancelled.
Unrepeatable read: when a transaction executes the same query twice, the query results differ because other transactions have modified or deleted the value in the middle.

ACID Properties of a Transaction

Atomicity: all data should be successfully entered or failed in one transaction.
Consistency: the transaction result should always be the same expected value, and the transaction should be controlled using Lock, Timestamp, Validation, etc. to prevent other transactions from intervening.
Isolation: another transaction should not intervene and process the data until transaction commit or rollback is issued.
Durability: the persistence of a successful transaction should be guaranteed, and the data should be restored using the forward recovery algorithm.

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Description

Learn about the definition and purposes of concurrency control in a database system that supports a multi-user environment. Understand how it enables the successful execution of multiple transactions simultaneously and ensures a serializable schedule.