Lecture - 1 Concurrency Control Introductory Lecture Fall2024

What are the four ACID properties of a valid transaction?

Atomic, Consistent, Isolated, Durable.

What does 'Atomic' mean in ACID properties?

A valid transaction is an atomic unit of processing, meaning there is no partial execution.

What is the purpose of the 'Consistent' property in transactions?

It ensures that the database goes from a consistent state to another consistent state after transaction execution.

What does 'Isolated' refer to in terms of transactions?

It means the transaction should not show uncommitted changes to other transactions.

Explain the concept of 'Durable' in ACID properties.

Once a transaction has been committed, its changes are permanent, even in the event of a system failure.

What are the two main files of a database?

Master Data File (MDF) and Log Data File (LDF).

Name a problem caused by concurrent execution of transactions.

Lost Update Problem, Dirty Read Problem, Incorrect Summary Problem, Unrepeatable Read Problem.

What is 'Recoverability' in the context of transaction scheduling?

It determines the ability to recover from a transaction failure without losing valid operations.

Define 'Serializable Schedule'.

A schedule is serializable if it is equivalent to a serial schedule of the same transactions.

What are the primary goals of concurrency control?

To enforce isolation, protect database consistency, and enforce serializability.

What is a lock in concurrency control?

A lock is a flag associated with a data item that controls access to it.

What are the two types of locks mentioned?

Binary Locks and Shared/Exclusive Locks.

What does the Two-Phase Locking Protocol (2PL) involve?

Locking operations precede the first unlock operation and consists of a growing phase followed by a shrinking phase.

What is the main principle of the conservative (static) version of 2PL?

A transaction should acquire all locks before it starts execution.

Can a schedule that follows the basic 2PL guarantee recoverability?

No, basic 2PL does not guarantee recoverability.

What ensures that Strict 2PL maintains serializability?

Strict 2PL does not allow unlocking of exclusive locks until the transaction commits or aborts.

What is the difference between Strict and Rigorous 2PL?

Rigorous 2PL does not release any locks until a commit or abort occurs, ensuring even stricter control over resource management.