Database Transactions and Concurrency Control

What is a transaction in a database?

• A collection of operations that form a single logical unit of work

• A request to read or write data in a database

• A constraint specified in the database schema

• A log used to track database updates

Which of the following is an example of a transaction?

• Writing a new customer's invoice

• Updating the sales in a database

• Reducing the quantity of on-hand products in inventory

• All of the above

What is a database request equivalent to in an application program or transaction?

• A single SQL statement

• A collection of SQL statements

• A database update

• A database query

What is a database consistent state?

• A state where all data is up-to-date

• A state where all data is accurate

• A state that satisfies the constraints specified in the schema

• A state that allows concurrent transactions

What is the purpose of a transaction log in a DBMS?

• To keep track of all the transactions that update the database

• To store the database schema

• To ensure data consistency

• To prevent deadlock

Which property of transactions ensures that all operations of a transaction are completed?

• Atomicity

• Consistency

• Isolation

• Durability

What does the consistency property of transactions ensure?

• Only valid data following all rules and constraints will be written in the database

• Data used during the execution of a transaction cannot be used by another transaction

• Once transaction changes are done and committed, they cannot be undone or lost

• All operations of a transaction should be completed

What does the isolation property of transactions ensure?

• All operations of a transaction should be completed

• Only valid data following all rules and constraints will be written in the database

• Data used during the execution of a transaction cannot be used by another transaction

• Once transaction changes are done and committed, they cannot be undone or lost

What does the durability property of transactions ensure?

• All operations of a transaction should be completed

• Only valid data following all rules and constraints will be written in the database

• Data used during the execution of a transaction cannot be used by another transaction

• Once transaction changes are done and committed, they cannot be undone or lost

What is a dirty read in transaction isolation levels?

• When a transaction reads data that is not committed yet

• When a transaction reads inconsistent data

• When a transaction reads data that has been modified by another transaction

• When a transaction reads additional rows that satisfy a query