This is a general question regarding Hibernate in a multi-threaded environment. I am writing a server that uses multiple threads to service an incoming queue of messages. Each thread attempts to write the results of it's processing to a common database through a Hibernate interface. So far so good. If I light off just one thread everhthing is fine; if I light off more than one I get stale object exceptions. I've looked at the adivce in the documentation and each thread opens a new connection to the database.

My question is simple - are stale object excepitions a feature of muti-threaded access or is there a general approach (locking?) that makes them go away? I can deal with the exceptions but I'd like not to see them in the first place.

Thanx,
Allan Clearwaters, The Object Forge

You say connection, but I hope you mean Session, right ?

If you get StaleObjectException, then you are having a good old transaction conflict - two users have written or deleted the same data!

From the javadoc:

"Thrown when a version number or timestamp check failed, indicating that the
* <tt>Session</tt> contained stale data (when using long transactions
* with versioning). Also occurs if we try delete or update a row that does
* not exist.<br>
* <br>
* Note that this exception often indicates that the user failed to specify the
* correct <tt>unsaved-value</tt> strategy for a class!"

So - is it the case for your app ? Are you having conflicting writes/deletes or are you specifying an incorrect value for unsaved-value ?

And wether you should start to use locking is all up to your application....

Max,

I do mean session as well but as I read the documentation it says "... never create more than one concurrent session or transaction per database connection"; it take this to mean that each thread should have it's own SessionFactory despite the assretion that SessionFactories are thread safe and intended to be shared (is this correct?).

It is certainly the case that individual threads may well modify the same object. I don't belived this is a versioning problem.

Any more insight would be most useful.

Thanx,
Al

No use 1 SessionFactory for all your threads and sf.openSession() for each thread. What is forbidden is to share the same connection object between several sessions


Since session object isn't thread safe, the don't share sessions between threads.

No - SessionFactory IS thread safe....but Session is not.
Use only a session in one thread at a time.

And regarding versioning - then it gotta be something about that since that is the only reason why you would get StaleObjectException!

When two threads can write to the same row in the database at the same time, then you should have some mechanisms to avoid inconsistency!
What do you do to prevent that ? Use optimistic locking and then report failure to the user or you use pessismistic locking and lock people out if necessary....basic database stuff ;)