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Cache definition-
Cache is a temporary data which is used to speed up the performance.
Types of caching in hibernate-
| Caching Level | Default On | Session-Specific | Query Results Cached | Objects Evicted | Concurrent Access | Usage | Code Snippets |
|---|---|---|---|---|---|---|---|
| First-level Cache | Yes | Yes | No | Yes | Thread-safe | Storing and retrieving entities within a single session | //Loading an entity from the first-level cache Session session = sessionFactory.openSession(); Employee employee = session.get(Employee.class, 1); |
| Second-level Cache | No | No | No | Configurable | Configurable | toring and retrieving entities across multiple sessions | //Enabling second-level cache true //Configuring second-level cache provider org.hibernate.cache.ehcache.EhCacheRegionFactory |
| Query Cache | No | No | Yes | Configurable | Configurable | Caching the results of a query | //Enabling query cache true //Using query cache Query query = session.createQuery(“from Employee”); query.setCacheable(true); List employees = query.list(); |
In the table above:
- Caching Level : The level of caching, whether it’s first-level, second-level, or query cache.
- Default On : Whether the cache is enabled by default or not.
- Session-Specific : Whether the cache is specific to a single session or not.
- Query Results Cached : Whether the cache stores the results of a query or not.
- Objects Evicted : Whether the cache automatically evicts stale objects or not.
- Concurrent Access : The level of concurrent access support provided by the cache.
- Usage : The use case for which the cache is best suited.
- Code Snippets : Examples of how to use the cache in code.
1-Session Cache/First level cache in hibernate-
- First level cache is enabled by default.
- First level cache can’t be disabled.
- Objects are retrieved from current session.
Example-
// Open a session
Session session = HibernateUtil.getSessionFactory().openSession();
// Begin a transaction
session.beginTransaction();
// Retrieve a customer object from the database
Customer customer = session.get(Customer.class, 1L);
// Print the customer's name
System.out.println(customer.getName());
// Retrieve the same customer object again
Customer customer2 = session.get(Customer.class, 1L);
// Print the customer's name again
System.out.println(customer2.getName());
// Commit the transaction
session.getTransaction().commit();
// Close the session
session.close();
In the above example, the first call to session.get(Customer.class, 1L) retrieves the customer object from the database and stores it in the first-level cache associated with the current session. The second call to session.get(Customer.class, 1L) retrieves the customer object from the first-level cache instead of hitting the database again.
It’s worth noting that the first-level cache is associated with a session, so if you open a new session, it will not have access to the objects stored in the first-level cache of the previous session.
Also, it’s important to note that hibernate’s first-level cache is enabled by default, so there is no need to do anything extra to enable it.
2- SessionFactory Cache/Second level cache in hibernate-
- Second level cache is disabled by default.
- Second level cache is configured to use.
- Objects can be retrieved from various sessions.
Extra-Query Level cache in hibernate-
- Query Cache is used to cache the results of a query.
- Stepes to enable query level cache-
step 1- Only add this line to configuration.
i.e. <property name=”hibernate.cache.use_query_cache”>true</property>
Github project link for all 3 Cache in hibernate – https://github.com/kuldeep101990/cacheInHibernate