Distributed Transactions

Question 1

What are Transactions?

Answer 1

A transaction is a set of related sequential operations that is guaranteed by the server to be atomic in the presence of multiple clients and server crashes.

Question 2

What are the Properties of database transactions intended to guarantee data validity?

Answer 2

-Atomicity: a transaction should be all or nothing
-Consistency: a transaction takes the system from one consistent state to another consistent state.
-Isolation: each transaction must be performed without interference.
-Durability: After a transaction has completed successfully, all its effects are saved in permanent storage.

Question 3

Locking is a concurrency control method. How does it work?

Answer 3

-Locks regulate access and ensure transaction isolation and data consistency.
-Lock set on each object just before it is accessed.
-Lock is labelled with the transaction identifier.
-Only the transaction that holds the lock can access the object.
-Locks removed when the transaction has completed.
-Can lead to deadlocks.

Question 4

What is Optimistic Concurrency Control?

Answer 4

-OCC transactions proceed optimistically assuming that conflicts are rare.
-It allows multiple transactions to proceed concurrently without blocking each other.

Question 5

What are the steps of OCC?

Answer 5

1.Set up
2.Read phase
3. Validation Phase
4.Commit Phase

Question 6

What are Timestamp Ordering steps?

Answer 6

1.Timestamp assignment.
2.Read and write operations.
3.Validation phase.
4.Commit or Abort.

Question 7

What are Dirty Reads?

Answer 7

A dirty read occurs when one transaction reads data that has been modified by another transaction that has not yet been comitted.

Question 8

What are Premature Writes?

Answer 8

A premature write is when multiple transactions attempt to write the same object or data item.