Query Cache | Caching | Hibernate Tutorial

What is Query Cache?

Query Cache is an optimization feature in Hibernate that allows the results of a query to be stored in memory. When the same query is executed again, Hibernate can retrieve the results from the cache instead of executing the query against the database, significantly improving performance and reducing database load.

How Does Query Cache Work?

When a query is executed, its results are stored in the Query Cache along with a unique identifier. If the same query is called again, Hibernate checks the cache for the results before contacting the database. This process can save time, especially for complex queries or large datasets.

Enabling Query Cache

To enable Query Cache in Hibernate, you need to configure it in your Hibernate configuration file (hibernate.cfg.xml) and annotate your entity classes appropriately.

Configuration Example

Add the following lines to your hibernate.cfg.xml:

<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>
<property name="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.EhCacheRegionFactory</property>

You also need to annotate your entity class with @Cacheable and specify the cache region.

Entity Example

Annotate your entity class like this:

@Entity
@Cacheable
@Cache(usage = CacheConcurrencyStrategy.READ_WRITE)
public class Product {
   @Id
   private Long id;
   private String name;
// getters and setters
}

Using Query Cache

Once the Query Cache is enabled and configured, you can use it in your queries. You can enable caching for specific queries using the setCacheable(true) method.

Query Example

Here is how to use the Query Cache in a Hibernate query:

Session session = sessionFactory.openSession();
Query query = session.createQuery("FROM Product");
query.setCacheable(true);
List products = query.list();
session.close();

Invalidating the Query Cache

It’s important to know that the Query Cache needs to be invalidated when the underlying data changes. This can be done using the evict() method on the cache region.

Cache Invalidation Example

Here is how to invalidate the cache:

Session session = sessionFactory.openSession();
session.beginTransaction();
// Update a Product
Product product = session.get(Product.class, productId);
product.setName("New Product Name");
session.update(product);
session.getSessionFactory().getCache().evictEntityRegion(Product.class);
session.getTransaction().commit();
session.close();

Conclusion

The Query Cache in Hibernate is a powerful feature that can significantly enhance the performance of your application by reducing the number of database calls for frequently executed queries. By enabling and configuring the query cache properly, you can improve the efficiency of your data retrieval operations.