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copied!<p>Single session. Start transaction when you need to do a set of operations (like update data after dialog box OK button), commit the tx at the end. The connection though is constantly open (since it's the same session), and thus all opportunities for caching can be used by both Hib and RDBMS.</p> <p>It may also be a good idea to implement a transparent session re-open in case the connection went dead -- users tend to leave applications open for extended periods of time, and it should continue to work Monday even if DB server was rebooted on weekend.</p> <p><strong>Update</strong></p> <p>Jens Schauder provided a reason to use multiple sessions: partial (unwanted) updates to the session. Well, that comes down to the way you use Hibernate. </p> <p>Suppose we have two dialogs open (as in Jens' blog example). If user clicks a radiobox, and we immediately update a Hibernate entity associated with this radiobox, then, when user clicks Cancel, we're in trouble -- session is already updated.</p> <p>The right way, as I see it, is to update dialog variables (non-Hibernate objects) only. Then, when user clicks OK, we begin a transaction, merge updated objects, commit the transaction. No garbage gets ever saved into session.</p> <pre><code>MyHibernateUtils.begin(); Settings settings = DaoSettings.load(); // update setttings here DaoSettings.save(settings); MyHibernateUtils.commit(); </code></pre> <p>If we implement such a clean separation of concerns, we can later switch to multiple sessions with a simple change of MyHibernateUtils.begin() implementation.</p> <p>As for possible memory leak, well... Transaction.commit() calls Session.flush(), which AFAIK, cleans the cache too. Also, one may manually control the caching policy by calling Session.setCacheMode().</p>

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