What's the use of session.flush() in Hibernate

Flushing the session forces Hibernate to synchronize the in-memory state of the Session with the database (i.e. to write changes to the database). By default, Hibernate will flush changes automatically for you:

• before some query executions
• when a transaction is committed

Allowing to explicitly flush the Session gives finer control that may be required in some circumstances (to get an ID assigned, to control the size of the Session,...).

As rightly said in above answers, by calling flush() we force hibernate to execute the SQL commands on Database. But do understand that changes are not "committed" yet. So after doing flush and before doing commit, if you access DB directly (say from SQL prompt) and check the modified rows, you will NOT see the changes.

This is same as opening 2 SQL command sessions. And changes done in 1 session are not visible to others until committed.

I only know that when we call session.flush() our statements are execute in database but not committed.

Suppose we don't call flush() method on session object and if we call commit method it will internally do the work of executing statements on the database and then committing.

commit=flush+commit (in case of functionality)

Thus, I conclude that when we call method flush() on Session object, then it doesn't get commit but hits the database and executes the query and gets rollback too.

In order to commit we use commit() on Transaction object.