Is Hibernate's session thread safe?

Question

I need to know, whether the Hibernate's session is thread safe or not. But obvious a new session is attached to every thread for execution. But my question is if in one thread I have updated some value of an entity, so will that be reflected in other thread during same time execution?

My problem is when I fire update from two threads sequentially, the value is updated properly but when I fire the update almost altogether then it fails.

for eg. current stage of table.

  ID      NAME      MARKS
------- --------- --------
  1       John       54

I am trying to do follwing :

Student student = session.load(Student.class, 1);
student.setMarks(student.getMarks() + 1);
session.update(student);
session.close();

When I try to run the above code in loop say 10, then value of "marks" in table "student" is properly updated i.e. the value gets updated to 64 which is proper.

But when I try to run the same code in threaded environment, it gives bad results.

Answer 1

It is not intended that implementors be threadsafe. Instead each thread/transaction should obtain its own instance from a SessionFactory.

Even with this in mind, your behaviour might still not be what you expect, because transactions come into play. You will have to set a proper transaction isolation level. See the configuration guide, hibernate.connection.isolation property.

Answer 2

Hibernate session and threads do not mix.

You should not use a session from multiple threads at once, and I recommend you only use a session from a single thread. DB session implementations are not even required to be theadsafe.

You also must consider what happens to the transactions when you start doing things in multiple threads. Transactions are tied to the current thread. This becomes quickly mindblowing and you enter areas where the implementers have not tested their products.

In the end life is too short to get lost in that swamp.