Spring Boot Transaction Management Concepts Questions and Answers

Question 1

An `OrderService` method, annotated with `@Transactional`, calls a public method in an `InventoryService` bean which is annotated with `@Transactional(propagation = Propagation.REQUIRES_NEW)`. If the `InventoryService` method completes successfully, but an unhandled exception is thrown later within the `OrderService` method, what will be the final state of the database changes?

Accepted Answer

Changes made by `InventoryService` will be committed, while changes made by `OrderService` will be rolled back.

Answer

`Propagation.REQUIRES_NEW` starts a completely new, independent transaction. It suspends the outer transaction (from `OrderService`), executes, and then commits or rolls back on its own. Since the `InventoryService` method completed successfully, its transaction was committed. The subsequent failure in `OrderService` causes its own transaction to roll back, but this does not affect the already-committed independent transaction of `InventoryService`.

Question 2

What is the primary benefit of marking a transactional method with `@Transactional(readOnly = true)` in a Spring Boot application using JPA and Hibernate?

Accepted Answer

It signals to the underlying persistence provider to apply performance optimizations, such as disabling dirty checking.

Answer

The main purpose of the `readOnly = true` flag is to serve as a hint for the persistence provider. For Hibernate, this allows it to apply significant optimizations, most notably skipping the costly dirty checking process (as it doesn't need to track changes) and not maintaining snapshots of entities. This reduces memory usage and CPU overhead, improving performance for read-heavy operations.

Question 3

In a Spring Boot application, if a public method in a `@Service` bean is annotated with just `@Transactional` and throws a `RuntimeException` during its execution, what is the expected default transactional behavior?

Accepted Answer

The transaction will be rolled back.

Answer

By default, Spring's declarative transaction management is configured to automatically trigger a rollback for any unchecked exceptions (`RuntimeException` and its subclasses) and `Error`s. It does not, by default, roll back for checked exceptions.

Question 4

A financial reporting service needs to run a long-running transaction that reads multiple rows, performs complex calculations, and then reads the same rows again to verify data consistency. It is critical that the data from the initial read does not change during the transaction. Which transaction isolation level should be used to prevent this "non-repeatable read" phenomenon?

Accepted Answer

REPEATABLE_READ

Answer

`REPEATABLE_READ` is the isolation level that guarantees if a row is read multiple times within the same transaction, the result will always be the same. It prevents both dirty reads and non-repeatable reads. `READ_COMMITTED` (a common default) only prevents dirty reads, allowing other transactions to modify and commit changes that would be visible on a subsequent read within the original transaction. `SERIALIZABLE` also prevents non-repeatable reads but is stricter, also preventing phantom reads at a higher concurrency cost.

Question 5

A developer has a Spring `@Service` bean with two public methods. The first method, `processData()`, is not transactional. It calls the second method within the same class, `saveData()`, which is annotated with `@Transactional`. When an external bean calls `processData()`, what happens to the transaction for the `saveData()` call?

Accepted Answer

The call to `saveData()` is executed, but no transaction is created.

Answer

Spring's declarative transaction management is implemented using AOP proxies. When an external bean calls a method, it goes through the proxy which applies the transactional advice. However, a method call within the same object (a self-invocation) bypasses the proxy and calls the method directly. Because the call to `saveData()` does not go through the proxy, the `@Transactional` annotation is not processed, and no transaction is started for that method call.

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Spring Boot Transaction Management Concepts Questions and Answers