Difference Betwixt Outset As Well As Mo Score Cache Inwards Hibernate

If you lot bring used Hibernate inward past times so you lot know that i of the strongest points of Hibernate framework is caching, which tin drastically amend the surgical procedure of Java application's persistence layer if configured too used correctly. Hibernate provides caching at many levels e.g. kickoff flat cache at Session level, 2d flat cache at the SessionFactory level, too query cache to cache oftentimes executed SQL queries. The kickoff flat cache minimizes database access for the same object. For example, if you lot telephone yell upward the get() method to access Employee object amongst id = 1 from i session, it volition acquire the database too charge the object into memory, but it volition also cache the object inward the kickoff flat cache.

When you lot volition telephone yell upward the get() method over again for the same object from the same session, fifty-fifty after doing roughly updates on the object, it volition render the object from the cache without accessing the database. You tin confirm this from Hibernate's log file past times observing how many queries are executed. This is also i of the oftentimes asked Hibernate Interview Questions, so it volition non entirely assistance to amend the surgical procedure of your Java application but also assistance you lot to produce good on your adjacent interview.

This session flat cache greatly improves the surgical procedure of Java application past times minimizing database roundtrips too executing less set out of queries. For example, if an object is modified several times inside the same transaction, so Hibernate volition entirely generate i SQL UPDATE arguing at the halt of the transaction, containing all the modification.


But, since this cache is associated amongst the Session object, which is a short-lived object inward Hibernate, equally shortly equally you lot unopen the session, all the information held inward the cache is lost. So, if you lot effort to charge the same object using the get() method, Hibernate volition acquire to the database over again too fetch the record.

This poses meaning surgical procedure challenge inward an application where multiple sessions are used, but you lot don't demand to worry. Hibernate provides roughly other application flat cache, known equally second flat cache, which tin survive shared amid multiple sessions. This agency a asking for the same object volition non acquire to the database fifty-fifty if it is executed from multiple session, provided object is acquaint inward the 2d flat cache.

The 2d flat cache is maintained at the SessionFactory level, which is used to opened upward sessions, thence every session is linked to SessionFactory. This cache is reverse to kickoff flat cache which is past times default enabled inward Hibernate, this i is past times default disabled too you lot demand to configure the 2d flat cache inward Hibernate configuration file to enable it.


The 2d flat cache is provided amongst the assistance of caching providers e.g. EhCache too OSCache. If you lot hold back at the cache bundle inward Hibernate, you lot tin meet the implementation of Caching related interfaces past times these providers. Depending upon which cache you lot desire to use, you lot tin configure them inward the Hibernate Configuration file.

Once configured, every asking for an object volition acquire to the 2d flat cache if it is non works life inward the first flat cache. It won't hitting the database without consulting 2d flat cache, which agency improved performance.

It's rattling of import for a Java too Hibernate developer to know nigh Caching inward Hibernate. It's non simply of import from Interview indicate of persuasion but also from the application evolution too surgical procedure improvement indicate of view. You volition often confront surgical procedure related challenges inward a existent globe application which incorporate millions of records, past times correctly configuring Hibernate sessions too writing code which brand operate of caching, your Java application tin float higher upward H2O fifty-fifty inward the instance of a meaning load. If you lot desire to acquire to a greater extent than nigh Hibernate performance, I advise reading  I advise reading High-Performance Java Persistence by Vlad Mihalcea, i of the best too up-to-date resources on hibernate surgical procedure at the moment.

Difference betwixt First too Second Level Cache inward Hibernate

Now that nosotros know what is kickoff flat too 2d flat cache inward Hibernate, let's revise roughly telephone commutation differences betwixt them from interview indicate of view.

Scope
First flat cache is associated amongst Session Object, piece the Second flat cache is associated amongst the SessionFactory object. This agency kickoff flat cache's compass is express to session flat piece 2d flat cache's compass is at the application level. Since Session object is created on demand from the SessionFactory too it's destroyed i time the session is closed, the same query if run from ii dissimilar sessions volition hitting the database twice if the 2d flat cache is non configured. On the other hand, 2d flat cache remains available throughout the application's life-cycle.


Configuration
First flat cache is past times default enabled inward Hibernate, piece the 2d flat cache is optional. If you lot demand it so you lot demand to explicitly enable the 2d flat cache on Hibernate configuration file i.e. the hibernate.cfg.xml file.

You tin operate the hibernate.cache.provider_class too hibernate.cache.use_second_level_cache properties to enable the 2d flat cache inward Hibernate. The kickoff i is the cite of the degree which implements Second flat cache too could survive different, depending upon which cache you lot operate e.g. EhCache or OSCache.

By default,  hibernate.cache.provider_class is prepare to org.hibernate.cache.NoCacheProvider class, which agency the 2d flat cache is disabled. You tin enable it past times setting something similar org.hibernate.cache.EhCacheProvider if you lot desire to operate EhCache equally the 2d flat cache.

Here is a sample configuration to configure Second flat cache amongst EhCache:

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

Don't forget to include hibernate-ehcache.jar into your classpath. This degree comes from that JAR. You tin also meet Java Persistence amongst Hibernate, 2nd edition to acquire to a greater extent than nigh other configuration options available to 2d flat cache.

Availability
First flat cache is available entirely until the session is open, i time the session is closed, the kickoff flat cache is destroyed. On the other hand, 2d flat cache is available through the application's life-cycle, it is entirely destroyed too recreated when you lot restart your application.


Order
If an entity or object is loaded past times calling the get() method so Hibernate kickoff checked the kickoff flat cache, if it doesn't works life the object so it goes to the 2d flat cache if configured. If the object is non works life so it finally goes to the database too returns the object, if at that topographic point is no corresponding row inward the tabular array so it render null. When an object is loaded from the database is set on both 2d flat too kickoff flat cache, so that other session who asking the same object tin straightaway acquire it from the 2d flat cache.

In instance if the object is non works life inward the kickoff flat cache but works life inward the 2d flat cache because roughly other sessions bring loaded the object earlier so it is non entirely returned from kickoff flat cache but also cached at kickoff flat cache, so that adjacent fourth dimension if your code asking the same object, it should survive returned from 1st flat cache rather than going to the 2nd flat cache.

save(), update(), or saveOrUpdate() method too retrieved past times load(), get(), list(), iterate(), or scroll() method, that object is added to the internal cache of the Session too when the flush() is later called, the the world of the object is sychronized amongst the database.

Second flat cache tin also survive configured on a per-class too per-collection basis, which agency it tin cache a degree or a collection. You tin operate class-cache too colleection-cache elements inward hibernate.cfg.xml to specify which degree or collection to cache at 2nd flat cache. You should shout back that 2d flat cache past times default doesn't cache whatever entitty until you lot configure it.

You tin also operate JPA Annoation @Cacheable to specify which entity is cacheable. too Hibernate annoation @Cache to specify caching startegy e.g. CacheConcurrencyStrategies similar READ_WRITE or READ_ONLY to say Hibernate how the 2d flat cache should behave.


That's all nigh difference betwixt kickoff too 2d flat cache inward Hibernate. It's non simply an ORM tool, hibernate is much to a greater extent than than that too in-built caching is i of the biggest produce goodness of using Hibernate to implement psersistence of DAO layer inward Hibernate. By correctly configuring 2d flat cache too writing code to leverage both kickoff flat too 2d flat cache inward Hibernate, you lot tin acquire improved surgical procedure inward Java application.

Further Learning
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Thanks for reading this article, if you lot similar this article too interview inquiry so delight percentage amongst your friends too colleagues. If you lot bring whatever inquiry or feedback so delight drib a comment.

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