Hibernate and multiple threads, synchronize changes between multiple users

Question

I am using Hibernate in an Eclipse RAP application. I have database tables mapped to classes with Hibernate and these classes have properties that are fetched lazily (If these weren't fetched lazily then I would probably end up loading the whole database into memory on my first query). I do not synchronize database access so there are multiple Hibernate Sessions for the users and let the DBMS do the transaction isolation. This means different instances of fetched data will belong to different users. There are things that if a user changes those things, then I would like to update those across multiple users. Currently I was thinking about using Hibernate session.refresh(object) in these cases to refresh the data, but I'm unsure how this will impact performance when refreshing multiple objects or if it's the right way to go.

Hope my problem is clear. Is my approch to the problem OK or is it fundamentally flawed or am I missing something? Is there a general solution for this kind of problem?

I would appreciate any comments on this.

Answer 1

The general solution is

• to have transactions as short as possible
• to link the session lifecycle to the transaction lifecycle (this is the default: the session is closed when the transaction is committed or rolled back)
• to use optimistic locking concurrency to avoid two transactions updating the same object at the same time.

If each transaction is very short and transaction A updates some object from O to O', then concurrent transaction B will only see O until it commits or rolls back, and any other transaction started after A will see O', because a new session starts with the transaction.