I must rewrite my last but one reply. I was trying it ones more how it behaves and the blocking I was writing about is not truth. Hello Alex, anonymous wrote : | No updates will be ever lost with higher isolation levels. The database will ensure that no two transactions that update the same data item can proceed. | Yes, I agree. If we set transaction to repeatable read isolation level, in my opinion optimistic locking does not work, because during whole transaction we always read same version of our row. The application can not see that another commited tx updated some row (bacause we have repeatable read). I think that optimistic locking needs non-repeatable read to work but jbpm docs says opposite. Regards Pavel View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4159422#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...