Distinction between First and Second Stage Cache in Hibernate [Answer]

When you have used Hibernate in previous then you recognize that one of many strongest factors of the Hibernate framework is caching, which might drastically enhance the efficiency of the Java software’s persistence layer if configured and used accurately. Hibernate supplies caching at many ranges e.g. first degree cache at Session degree, second-level cache on the SessionFactory degree, and question cache to cache regularly executed SQL queries. The primary degree cache minimizes database entry for a similar object. For instance, should you name the get() methodology to entry Worker object with id = 1 from one session, it can go to the database and cargo the thing into reminiscence, however it can additionally cache the thing within the first-level cache.

When you’ll name the get() methodology once more for a similar object from the identical session, even after doing a little updates on the thing, it can return the thing from the cache with out accessing the database. You may affirm this from Hibernate’s log file by observing what number of queries are executed.

That is additionally one of many regularly requested Hibernate Interview Questions, so it is not going to solely assist to enhance the efficiency of your Java software but additionally enable you to to do nicely in your subsequent interview.

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This session-level cache enormously improves the efficiency of Java functions by minimizing database roundtrips and executing fewer queries. For instance, if an object is modified a number of instances inside the similar transaction, then Hibernate will solely generate one SQL UPDATE assertion on the finish of the transaction, containing all of the modifications.

However, since this cache is related to the Session object, which is a short-lived object in Hibernate, as quickly as you shut the session, all the data held within the cache is misplaced. So, should you attempt to load the identical object utilizing the get() methodology, Hibernate will go to the database once more and fetch the document.

This poses a major efficiency problem in an software the place a number of periods are used, however you need not fear. Hibernate supplies one other application-level cache, often called second-level cache, which could be shared amongst a number of periods. This implies a request for a similar object is not going to go to the database even whether it is executed from a number of periods, the offered object is current within the second-level cache.

The second-level cache is maintained on the SessionFactory degree, which is used to open periods, therefore each session is linked to SessionFactory. This cache is reverse to first degree cache which is by default enabled in Hibernate, this one is by default disabled and you should configure the second degree cache in Hibernate configuration file to allow it.

The second-level cache is supplied with the assistance of caching suppliers e.g. EhCache and OSCache. In the event you take a look at the cache package deal in Hibernate, you’ll be able to see the implementation of Caching associated interfaces by these suppliers. Relying upon which cache you need to use, you’ll be able to configure them within the Hibernate configuration file.

As soon as configured, each request for an object will go to the second degree cache if it’s not discovered within the first degree cache. It will not hit the database with out consulting second-level cache, which suggests improved efficiency.

It is essential for a Java and Hibernate developer to learn about Caching in Hibernate. It isn’t simply vital from the Interview viewpoint but additionally from the appliance growth and efficiency enchancment viewpoint.

You’ll typically face performance-related challenges in a real-world software which comprise hundreds of thousands of data, by accurately configuring Hibernate periods and writing code which make use of caching, your Java software can float above water even within the case of a major load.

If you wish to be taught extra about Hibernate’s efficiency, I recommend studying  I recommend studying Excessive-Efficiency Java Persistence e-book by Vlad Mihalcea, top-of-the-line and up-to-date sources on hibernate efficiency in the meanwhile.

Distinction between First and Second Stage Cache in Hibernate

Now that we all know what’s first degree and second degree cache are in Hibernate, let’s revise some key variations between them from the interview viewpoint.

1. Scope

The primary degree cache is related to the Session Object, whereas the second-level cache is related to the SessionFactory object. This implies first-level cache’s scope is proscribed to session-level whereas second-level cache’s scope is on the software degree.

For the reason that Session object is created on-demand from the SessionFactory and it is destroyed as soon as the session is closed, the identical question is run from two completely different periods will hit the database twice if the second-level cache just isn’t configured.

However, second-level cache stays accessible all through the appliance’s life cycle.

2. Configuration

The primary degree cache is by default enabled in Hibernate, whereas the second degree cache is elective. In the event you want it then you should explicitly allow the second degree cache on the Hibernate configuration file i.e. the hibernate.cfg.xml file.

You should use the hibernate.cache.provider_class and hibernate.cache.use_second_level_cache properties to allow the second degree cache in Hibernate. The primary one is the identify of the category which implements Second degree cache and could possibly be completely different, relying upon which cache you utilize like EhCache or OSCache.

By default,  hibernate.cache.provider_class is about to org.hibernate.cache.NoCacheProvider class, which suggests the second-level cache is disabled. You may allow it by setting one thing like org.hibernate.cache.EhCacheProvider if you wish to use EhCache because the second-level cache.

Here’s a pattern configuration to configure Second degree cache with EhCache:

<prop key="hibernate.cache.use_second_level_cache">true</prop>
<prop key="hibernate.cache.provider_class">
org.hibernate.cache.EhCacheProvider
</prop>

Do not forget to incorporate hibernate-ehcache.jar into your classpath. This class comes from that JAR. You too can see Java Persistence with Hibernate, 2nd version to be taught extra about different configuration choices accessible to the second-level cache.

3. Availability

The primary degree cache is on the market solely till the session is open, as soon as the session is closed, the primary degree cache is destroyed. However, the second-level cache is on the market via the appliance’s life-cycle, it is just destroyed and recreated once you restart your software.

4. Order

If an entity or object is loaded by calling the get() methodology then Hibernate first checked the primary degree cache, if it would not discover the thing then it goes to the second degree cache if configured. If the thing just isn’t discovered then it lastly goes to the database and returns the thing, if there isn’t any corresponding row within the desk then it returns null.

When an object is loaded from the database is placed on each second degree and first-level cache, in order that different session who request the identical object can now get it from the second-level cache.

In case if the thing just isn’t discovered within the first degree cache however discovered within the second degree cache as a result of another periods have loaded the thing earlier than then it’s not solely returned from the primary degree cache but additionally cached on the first degree cache, in order that subsequent time in case your code request the identical object, it needs to be returned from 1st degree cache slightly than going to the 2nd degree cache.

Usually. When an object is cross to save(), replace(), or saveOrUpdate() methodology and retrieved by load(), get(), listing(), iterate(), or scroll() methodology, that object is added to the interior cache of the Session and when the flush() is subsequently referred to as, the state of the thing is synchronized with the database.

The second-level cache may also be configured on a per-class and per-collection foundation, which suggests it will possibly cache a category or a set. You should use class-cache and collection-cache parts in hibernate.cfg.xml to specify which class or assortment to cache at 2nd degree cache. You must do not forget that second-level cache by default would not cache any entity till you configure it.

You too can use JPA Annotation @Cacheable to specify which entity is cacheable. and Hibernate annotations @Cache to specify caching technique like CacheConcurrencyStrategies like READ_WRITE or READ_ONLY to inform Hibernate how the second degree cache ought to behave.

That is all in regards to the distinction between first and second degree cache in Hibernate. It isn’t simply an ORM software, hibernate is rather more than that and in-built caching is without doubt one of the largest advantages of utilizing Hibernate to implement persistence of DAO layer in Hibernate. By accurately configuring second-level cache and writing code to leverage each first-level and second-level cache in Hibernate, you may get improved efficiency in Java functions.

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