A transaction manager is which of the following?

Solution (By Examveda Team)

A transaction manager in a distributed database system performs several critical functions to ensure the correctness, reliability, and consistency of transactions.

Option A: Maintains a log of transactions
The transaction manager is responsible for maintaining a log of all transactions executed in the system. This transaction log records details such as the operations performed by each transaction, timestamps, and transaction identifiers. The log serves as a record of the database's state changes and enables recovery in the event of system failures or crashes. By logging transactions, the system can ensure atomicity and durability properties of transactions.

Option B: Maintains before and after database images
In addition to maintaining a transaction log, the transaction manager often maintains before and after images of the database state for each transaction. These images represent the state of the database before and after the transaction's execution. By capturing these snapshots, the system can facilitate rollback operations during transaction aborts or recovery processes. Before and after images are essential for ensuring transaction consistency and integrity.

Option C: Maintains appropriate concurrency control
Concurrency control is vital for managing concurrent access to shared resources in a distributed database environment. The transaction manager implements concurrency control mechanisms to ensure that transactions execute serializably and without interfering with each other. Techniques such as locking, timestamp ordering, and optimistic concurrency control are commonly employed to manage concurrency effectively. By maintaining appropriate concurrency control, the transaction manager prevents data anomalies, such as lost updates and inconsistent reads, thereby preserving database consistency.

Option D: All of the above
All the mentioned functions—maintaining transaction logs, before and after database images, and appropriate concurrency control—are essential responsibilities of the transaction manager in a distributed database system. Together, these functions contribute to the ACID properties of transactions (Atomicity, Consistency, Isolation, Durability) and ensure the reliability and correctness of the database operations.

Therefore, in the context of a transaction manager in a distributed database system, the correct option is All of the above (Option D).