Because hibernate does write behind transaction, does it mean that when i call session.beginTransaction();, hibernate may not actually start transaction, rather, it will first try to resolve all data integrity/dependency issues mentioned via configuration files and once found valid, it will open a transaction, execute sql and commit. this will ensure that transaction is opened for min. amount of time. OR does hibernate open transaction when i call session.beginTransaction() ?

I believe it's pretty pro-active. When you call for a transaction to start, it's started.