What is the role of the 'rollback' statement in transaction management?
- Committing the changes made by the current transaction
- Ending the current transaction
- Initiating a new transaction
- Reversing the changes made by the current transaction
The 'rollback' statement in transaction management is used to undo the changes made by the current transaction. If an error occurs or a condition is met, the 'rollback' command ensures that all changes made so far in the transaction are rolled back, maintaining data consistency.
What is the difference between 'dirty read' and 'non-repeatable read' in the context of transaction isolation levels?
- Dirty read: Reading committed data
- Dirty read: Reading uncommitted data
- Non-repeatable read: Reading committed data
- Non-repeatable read: Reading uncommitted data
In the context of transaction isolation levels, a 'dirty read' occurs when a transaction reads uncommitted data from another transaction, while a 'non-repeatable read' happens when a transaction reads data committed by another transaction but the data changes before the first transaction completes. Understanding these concepts is crucial in managing data consistency and isolation in concurrent transactions.
How do distributed transactions differ from local transactions?
- Concurrency and Durability
- Consistency and Recovery
- Isolation and Atomicity
- Scope and Participants
Distributed transactions involve multiple participants and a wider scope, whereas local transactions are limited to a single resource or database.
What is two-phase commit protocol in the context of transaction management?
- A protocol for authentication
- A protocol for coordination
- A protocol for data retrieval
- A protocol for voting
The two-phase commit protocol is a coordination protocol involving a voting phase and a decision phase to ensure distributed transaction consistency.
How do savepoints work within a transaction?
- Allow for partial rollback
- Commit the entire transaction
- Isolate a transaction
- Terminate the transaction
Savepoints allow for partial rollback within a transaction, providing a way to undo part of the transaction without affecting the entire operation.
In SQL, the command ________ is used to permanently save changes made by the current transaction.
- BEGIN TRANSACTION
- COMMIT
- ROLLBACK
- SAVEPOINT
The COMMIT command in SQL is used to permanently save changes made by the current transaction.
The isolation level that allows neither dirty reads nor non-repeatable reads is called _________.
- Read Committed
- Read Uncommitted
- Repeatable Read
- Serializable
The Serializable isolation level ensures neither dirty reads nor non-repeatable reads, providing the highest level of isolation.
The concept of ________ allows multiple users to make changes to the database without affecting each other.
- Concurrency Control
- Consistency Management
- Isolation
- Transaction Control
The concept of Concurrency Control allows multiple users to make changes to the database concurrently without affecting each other, ensuring data integrity and consistency.
In a distributed system, when two databases must be updated as part of a single transaction, which transaction management technique is most appropriate?
- Isolation (I)
- Optimistic Concurrency Control (OCC)
- Pessimistic Concurrency Control (PCC)
- Two-Phase Commit (2PC)
The Two-Phase Commit (2PC) is most appropriate for managing transactions in a distributed system involving updates to multiple databases, ensuring atomicity and consistency across the distributed environment.
In JDBC, how can you ensure that all resources are freed, even if an SQL exception occurs?
- Close resources in the catch block
- Implement a custom resource management mechanism
- Resources are automatically freed in JDBC
- Use the finally block to close resources
Using the finally block ensures that resources (like connections, statements, result sets) are closed, even if an SQL exception occurs, promoting proper resource management and avoiding leaks.