What is Persistence Context?

A persistence context handles a set of entities which hold data to be persisted in some persistence store (e.g. a database). In particular, the context is aware of the different states an entity can have (e.g. managed, detached) in relation to both the context and the underlying persistence store.

Although Hibernate-related (a JPA provider), I think these links are useful:

http://docs.jboss.org/hibernate/core/4.0/devguide/en-US/html/ch03.html

http://docs.jboss.org/hibernate/entitymanager/3.5/reference/en/html/architecture.html

In Java EE, a persistence context is normally accessed via an EntityManager.

http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html

The various states an entity can have and the transitions between these are described below:

http://docs.jboss.org/hibernate/entitymanager/3.6/reference/en/html/objectstate.html

https://vladmihalcea.com/wp-content/uploads/2014/07/jpaentitystates.png

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Entities are managed by javax.persistence.EntityManager instance using persistence context. Each EntityManager instance is associated with a persistence context. Within the persistence context, the entity instances and their lifecycle are managed. Persistence context defines a scope under which particular entity instances are created, persisted, and removed. A persistence context is like a cache which contains a set of persistent entities , So once the transaction is finished, all persistent objects are detached from the EntityManager's persistence context and are no longer managed.

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Taken from this page:

Here's a quick cheat sheet of the JPA world:

A Cache is a copy of data, copy meaning pulled from but living outside the database.

Flushing a Cache is the act of putting modified data back into the database.

A PersistenceContext is essentially a Cache. It also tends to have it's own non-shared database connection.

An EntityManager represents a PersistenceContext (and therefore a Cache)

An EntityManagerFactory creates an EntityManager (and therefore a PersistenceContext/Cache)

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A persistent context represents the entities which hold data and are qualified to be persisted in some persistent storage like a database. Once we commit a transaction under a session which has these entities attached with, Hibernate flushes the persistent context and changes(insert/save, update or delete) on them are persisted in the persistent storage.

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Both the org.hibernate.Session API and javax.persistence.EntityManager API represent a context for dealing with persistent data.

This concept is called a persistence context. Persistent data has a state in relation to both a persistence context and the underlying database.

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Persistence Context is an environment or cache where entity instances(which are capable of holding data and thereby having the ability to be persisted in a database) are managed by Entity Manager.It syncs the entity with database.All objects having @Entity annotation are capable of being persisted. @Entity is nothing but a class which helps us create objects in order to communicate with the database.And the way the objects communicate is using methods.And who supplies those methods is the Entity Manager.

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"A set of persist-able (entity) instances managed by an entity manager instance at a given time" is called persistence context.

JPA @Entity annotation indicates a persist-able entity.

Refer JPA Definition here

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In layman terms we can say that Persistence Context is an environment where entities are managed, i.e it syncs "Entity" with the database.

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While @pritam kumar gives a good overview the 5th point is not true.

Persistence Context can be either Transaction Scoped-- the Persistence Context 'lives' for the length of the transaction, or Extended-- the Persistence Context spans multiple transactions.

https://blogs.oracle.com/carolmcdonald/entry/jpa_caching

JPA's EntityManager and Hibernate's Session offer an extended Persistence Context.

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