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    <p>I would use a session per request to the server, and one transaction per session. I wouldn't optimize for performance before the app is mature.</p> <p>Answer to your solutions: </p> <ul> <li>Have a single session that's always opened that all clients use: You will have performance issues here because the session is not thread safe and you will have to lock all calls to the session.</li> <li>Have a single session for each client that connects and periodically flush it: You will have performance issues here because all data used by the client will be cached. You will also see problems with stale data from the cache.</li> <li>Open a session every time I have to use any of the persisted entities and close it as soon as the update, insert, delete or query is complete: You won't have any performance problems here. A disadvantage are possible concurrency or corrupt data problems because related sql statements are not executed in the same transaction.</li> <li>Have a session for each client, but keep it disconnected and only reconnect it when I need to use it: NHibernate already has build-in connection management and that is already very optimized. </li> <li>Same as above, but keep it connected and only disconnect it after a certain period of inactivity: Will cause problems because the amount of sql connections is limited and will also limit the amount of users of your application.</li> <li>Keep the entities detached and only attach them every 10 minutes, say, to commit the changes: Will cause problems because of stale data in the detached entities. You will have to track changes yourself, which makes you end up with a piece of code that looks like the session itself.</li> </ul> <p>It would be useless to go into more detail now, because I would just repeat the manuals/tutorials/book. When you use a session per request, you probably won't have problems in 99% of the application you describe (and maybe not at all). Session is a lightweight not threadsafe class, that to live a very short. When you want to know exactly how the session/connection/caching/transaction management works, I recommend to read a manual first, and than ask some more detailed questions about the unclear subjects.</p>
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    1. COI'm not trying to optimize it; I'm just trying to figure out what the different methods are of doing it, what they're generally good or not good for, how well they scale and perform etc. before commiting to one. It's about making sure I don't do anything stupid and choose a reasonably sensible solution. Not performance tuning. So, as for your answer, what do you mean by "request" - what "request"? You mean each time a player does something?
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    2. COYes with request I mean "each time a player does something" or "each call from the client to the server"
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    3. COHaving read the edits you added in later, I have one question about something you said. Regarding having a single session per client, I thought that NHibernate guarantees that methods like ISession.Find won't ever return stale data. Secondly, you seemed to be discouraging using Reconnect/Disconnect because "NHibernate already has build-in connection management" yet the manual uses that in a concurrency example called "Long session with automatic versioning".
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