ORM Caching Strategies

Well, well, well! Grab your hiking gear because we're about to explore the high peaks of Hibernate/JPA caching.

Now, imagine you're going to your favorite cafe and ordering the same grande, iced, sugar-free, vanilla latte with soy milk every day. Would it make sense for the barista to ask for your order every time? Of course not, that's where caching comes in, saving the day...and our order!

Hibernate/JPA provides a similar feature, with two levels of caching to boost your application's performance:

1. First-Level Cache: This is enabled by default and exists for the lifespan of a session. Every time a session retrieves an entity, it's stored in the session-level cache and reused whenever needed within that same session. However, this is a short-lived cache and isn't shared between different sessions.

2. Second-Level Cache: Unlike the first level, the second-level cache is session-independent. It's not enabled by default and needs to be configured manually. The entities in this cache are available across sessions and can significantly improve performance for read-heavy applications.

Ready to ascend to the second level, are we? Excellent! Here's how we enable the second-level cache in Hibernate:

Step 1: Add your caching provider to your pom.xml or build.gradle. For instance, if you are using EhCache, you'd do:

Maven:

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-ehcache</artifactId>
    <version>5.4.32.Final</version>
</dependency>

Gradle:

implementation 'org.hibernate:hibernate-ehcache:5.4.32.Final'

Step 2: Configure Hibernate to use the second level cache by adding these properties in your persistence.xml or hibernate.cfg.xml:

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

Step 3: Enable caching for specific entities by adding @Cacheable(true) and specify the caching strategy. For instance:

@Entity
@Cacheable(true)
@org.hibernate.annotations.Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class Book {
    // Your fields, constructors, getters and setters...
}

The usage attribute specifies the cache strategy to use. READ_ONLY is a simple strategy suitable for entities that never change. Other strategies include READ_WRITE, NONSTRICT_READ_WRITE and TRANSACTIONAL based on your specific requirements and use cases.

Et voila! You've activated the second level. Your database can now breathe a sigh of relief.

// Assuming we have an EntityManager "em"

// Read without cache
Book book = em.find(Book.class, 1L);

// Now let's update the book
book.setTitle("New Title");

// Clear the persistence context, simulating a new session
em.clear();

// Read the book again
Book updatedBook = em.find(Book.class, 1L);

In this code snippet, without enabling the second-level cache, the find() method will hit the database twice, once for each call. But if we enable the second-level cache, the second find() will retrieve the book from the cache, not the database. Pretty cool, huh? Your database is already thanking you for fewer hits!

Remember to use this wisely, though. While it's tempting to cache everything like a squirrel with acorns, incorrect caching can lead to outdated data if your data changes frequently. So cache responsibly, dear readers! And remember, not everything that glitters is gold, and not everything that can be cached should be.

Now, go and cache your world...within reason!