Hibernate First-Level Cache in Spring Boot

This project demonstrates how Hibernate's first-level cache operates within a Spring Boot application using JPA. It includes two endpoints that highlight the cache's behavior: one where the cache is not utilized due to separate transactions, and another where it is effectively used within a single transaction.

Project Components

• CustomerEntity: A JPA entity representing the customer table in the database.
• CustomerRepository: A Spring Data JPA repository extending JpaRepository for CRUD operations on CustomerEntity.
• CustomerController: A REST controller with two endpoints to showcase first-level cache behavior:
  • /without-first-level-cache: Shows the absence of caching when repository methods run in separate transactions (Sessions).
  • /with-first-level-cache: Demonstrates caching within a single transaction (same session) using @Transactional.

Scenarios

1. Without First-Level Cache (/without-first-level-cache)

This endpoint calls save and findById from CustomerRepository without an explicit @Transactional annotation on the controller method. As a result, each repository method executes in its own transaction, each with a separate persistence context.

Behavior

• Transaction for save: A new transaction begins, persists the customer entity to the database, and caches it in the persistence context. The transaction then commits and closes, ending the persistence context.
• Transaction for findById: A new transaction starts with its own persistence context. Since it doesn’t share the previous context, the entity isn’t available in the cache, and a SELECT query fetches it from the database.

Log Evidence

2025-03-19T21:54:51.184+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.save]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT
2025-03-19T21:54:51.184+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Opened new EntityManager [SessionImpl(810818063<open>)] for JPA transaction
2025-03-19T21:54:51.184+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@3b283604]
2025-03-19T21:54:51.185+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] org.hibernate.SQL                        : /* insert for dev.hamze.jpa.test.CustomerEntity */insert into customer (date_of_birth,first_name,last_name,id) values (?,?,?,default)
2025-03-19T21:54:51.185+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Initiating transaction commit
2025-03-19T21:54:51.186+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Committing JPA transaction on EntityManager [SessionImpl(810818063<open>)]
2025-03-19T21:54:51.186+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Closing JPA EntityManager [SessionImpl(810818063<open>)] after transaction
2025-03-19T21:54:51.186+03:30  INFO 1289930 --- [jpa-test] [nio-8080-exec-6] dev.hamze.jpa.test.CustomerController    : Customer saved without first level cache: CustomerEntity(customerId=5, firstName=John, lastName=Doe, dateOfBirth=2025-03-19)
2025-03-19T21:54:51.186+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Creating new transaction with name [org.springframework.data.jpa.repository.support.SimpleJpaRepository.findById]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly
2025-03-19T21:54:51.186+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Opened new EntityManager [SessionImpl(439371427<open>)] for JPA transaction
2025-03-19T21:54:51.186+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@5a909c5d]
2025-03-19T21:54:51.187+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] org.hibernate.SQL                        : select ce1_0.id,ce1_0.date_of_birth,ce1_0.first_name,ce1_0.last_name from customer ce1_0 where ce1_0.id=?
2025-03-19T21:54:51.187+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Initiating transaction commit
2025-03-19T21:54:51.187+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Committing JPA transaction on EntityManager [SessionImpl(439371427<open>)]
2025-03-19T21:54:51.187+03:30 DEBUG 1289930 --- [jpa-test] [nio-8080-exec-6] o.s.orm.jpa.JpaTransactionManager        : Closing JPA EntityManager [SessionImpl(439371427<open>)] after transaction
2025-03-19T21:54:51.187+03:30  INFO 1289930 --- [jpa-test] [nio-8080-exec-6] dev.hamze.jpa.test.CustomerController    : Customer found without first level cache: Optional[CustomerEntity(customerId=5, firstName=John, lastName=Doe, dateOfBirth=2025-03-19)]

• Key Observations:
  • Two distinct transactions are created: one for save and one for findById.
  • Each transaction uses a separate EntityManager (persistence context), which closes after the transaction ends.
  • A SELECT query in the findById transaction confirms the entity wasn’t retrieved from the cache.

2. With First-Level Cache (/with-first-level-cache)

This endpoint is annotated with @Transactional, ensuring that save and findById execute within the same transaction and share a single persistence context.

Behavior

• Single Transaction: Both save and findById run in one transaction, sharing the same persistence context.
• Cache Utilization: After save persists the entity, it’s cached in the persistence context. The subsequent findById retrieves it from the cache without issuing a SELECT query.

Log Evidence

2025-03-19T21:56:01.566+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Creating new transaction with name [dev.hamze.jpa.test.CustomerController.withFirstLevelCache]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT
2025-03-19T21:56:01.566+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Opened new EntityManager [SessionImpl(2067982765<open>)] for JPA transaction
2025-03-19T21:56:01.566+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Exposing JPA transaction as JDBC [org.springframework.orm.jpa.vendor.HibernateJpaDialect$HibernateConnectionHandle@62535865]
2025-03-19T21:56:01.566+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Found thread-bound EntityManager [SessionImpl(2067982765<open>)] for JPA transaction
2025-03-19T21:56:01.566+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Participating in existing transaction
2025-03-19T21:56:01.567+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] org.hibernate.SQL                        : /* insert for dev.hamze.jpa.test.CustomerEntity */insert into customer (date_of_birth,first_name,last_name,id) values (?,?,?,default)
2025-03-19T21:56:01.567+03:30  INFO 1289930 --- [jpa-test] [io-8080-exec-10] dev.hamze.jpa.test.CustomerController    : Customer saved with first level cache: CustomerEntity(customerId=6, firstName=John, lastName=Doe, dateOfBirth=2025-03-19)
2025-03-19T21:56:01.567+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Found thread-bound EntityManager [SessionImpl(2067982765<open>)] for JPA transaction
2025-03-19T21:56:01.567+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Participating in existing transaction
2025-03-19T21:56:01.568+03:30  INFO 1289930 --- [jpa-test] [io-8080-exec-10] dev.hamze.jpa.test.CustomerController    : Customer found with first level cache: Optional[CustomerEntity(customerId=6, firstName=John, lastName=Doe, dateOfBirth=2025-03-19)]
2025-03-19T21:56:01.568+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Initiating transaction commit
2025-03-19T21:56:01.568+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Committing JPA transaction on EntityManager [SessionImpl(2067982765<open>)]
2025-03-19T21:56:01.568+03:30 DEBUG 1289930 --- [jpa-test] [io-8080-exec-10] o.s.orm.jpa.JpaTransactionManager        : Closing JPA EntityManager [SessionImpl(2067982765<open>)] after transaction

• Key Observations:
  • One transaction spans the entire method, using a single EntityManager.
  • The "Participating in existing transaction" log indicates save and findById share the same context.
  • No SELECT query is logged for findById, proving the entity was retrieved from the cache.

Conclusion

This project highlights the role of transactional context in Hibernate’s first-level cache:

• Without @Transactional: Separate transactions create isolated persistence contexts, preventing cache reuse and requiring database queries.
• With @Transactional: A shared transaction enables the same persistence context, allowing the cache to optimize performance by avoiding redundant queries.