Question

A transaction T1 may read a given value from a table. If another transaction T2 later updates that value and T1 reads that value again, T1 will see a _____?

1) Different value
2) Same value
3) Null value
4) Error

Answer 1

T1 will see a different value after T2 updates that value, depending on the database's isolation level.

Step-by-step explanation:

When a transaction T1 reads a value from a table and a different transaction T2 updates that value, if T1 reads the value again, T1 will see a different value. However, this behavior can vary based on the isolation level of the database transactions. In databases with higher isolation levels like Serializable, T1 would not see the update from T2 until after T1 has completed, to maintain consistency. But in lower isolation levels such as Read Committed, which is typically the default, T1 would indeed see a different value when it reads the same data after T2 has made the update and the transaction is committed.