Query Cache in Hibernate

Query Cache in Hibernate

Query Cache  in Hibernate is a caching mechanism that stores the results of queries for reuse. This is particularly useful for queries that are executed frequently but return the same results. By caching the results of these queries, Hibernate can avoid hitting the database multiple times, thereby improving performance.

Key Points:

1.  Second-Level Cache : Query cache works in conjunction with Hibernate’s second-level cache. While the second-level cache stores entities, the query cache stores the actual query results.

2.  Configurable : The query cache can be configured for specific queries to ensure that only the required queries are cached.

3.  Performance Optimization : By reducing the number of database hits, the query cache can significantly improve the performance of read-heavy applications.

4.  Automatic Invalidation : If an entity involved in a cached query result is updated or deleted, Hibernate will automatically invalidate the corresponding cached query results to maintain data consistency.

Query Cache in Hibernate

Java Example with Query Cache

To use query cache in Hibernate, you need to enable it in the configuration and also enable caching for the specific query.

Configuration:

 hibernate.cfg.xml 
xml
<hibernate-configuration>
    <session-factory>
        <!-- Other configuration properties -->

        <!-- Enable second-level cache -->
        <property name="hibernate.cache.use_second_level_cache">true</property>
        <property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>
        
        <!-- Enable query cache -->
        <property name="hibernate.cache.use_query_cache">true</property>
    </session-factory>
</hibernate-configuration>


Entity Configuration:

 Employee.java 
java
@Entity
@Cacheable
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Employee {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @ManyToOne
    @JoinColumn(name = "department_id")
    private Department department;

    // Getters and Setters
}


Using Query Cache:
 3. Using Query Cache: 

 Querying with Cache: 
java
Session session = sessionFactory.openSession();
Transaction transaction = session.beginTransaction();

// Query with cache enabled
String hql = "FROM Employee e WHERE e.department.name = :departmentName";
Query query = session.createQuery(hql);
query.setParameter("departmentName", "HR");
query.setCacheable(true); // Enable caching for this query
List<Employee> employees = query.list();

for (Employee employee : employees) {
    System.out.println(employee.getName());
}

transaction.commit();
session.close();


Example of Query Cache in Hibernate

  • The query results are cached because query.setCacheable(true) is used.
  • The query cache works in conjunction with the second-level cache, which must be enabled and configured.

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