What is First and Second Level caching in Hibernate?

Question

in simple words, any one?

Answer 1

1.1) First-level cache

First-level cache always Associates with the Session object. Hibernate uses this cache by default. Here, it processes one transaction after another one, means wont process one transaction many times. Mainly it reduces the number of SQL queries it needs to generate within a given transaction. That is instead of updating after every modification done in the transaction, it updates the transaction only at the end of the transaction.

1.2) Second-level cache

Second-level cache always associates with the Session Factory object. While running the transactions, in between it loads the objects at the Session Factory level, so that those objects will available to the entire application, don’t bounds to single user. Since the objects are already loaded in the cache, whenever an object is returned by the query, at that time no need to go for a database transaction. In this way the second level cache works. Here we can use query level cache also. Later we will discuss about it.

Quoted from: http://www.javabeat.net/articles/37-introduction-to-hibernate-caching-1.html

Answer 2

Theres a pretty good explanation of first level caching on the Streamline Logic blog

Bascially, first level caching happens on a per session basis where as second level caching can be shared across multiple sessions.