What are the drawbacks to leaving a Hibernate Session open for a really long time? I'm working on a DB-backed DESKTOP app (using Java SE 5, not a web app, not Java EE) that constantly needs to gather more info from the DB as the user decides to look at various screens, etc.

The biggest place where this occurs is in a tree-like viewer. When the user expands nodes, the DB is queried for the child nodes. I would like to be able to simply start one Session for the tree viewer and leave it open until the tree viewer screen is closed.

Does this sound reasonable to anyone?
What's wrong, if anything, with this plan?

What you describe is called the "Session-per-conversation" pattern and is documented in Chapter 11.3.2 of the reference manual.

http://www.hibernate.org/hib_docs/v3/re ... ongsession

The longer you leave it open, the more stale the data you have cached in your session becomes--other users could have modified it. Hibernate checks instance versions when you flush your changes to the database, throwing an exception if concurrent modification is detected. It is up to you the developer to catch and handle this exception in an intelligent way. Common options are the opportunity for the user to merge changes or to restart the business conversation with non-stale data.

Bruce