db4o best practice to query objects from db

I am using two different ways to query objects in db4o and I would like to discuss about it.

1) In this first example, I create an instance of ObjectContainer, I open the connection, and then I close it.

ObjectContainer db = Db4oEmbedded.openFile(Db4oEmbedded.newConfiguration(), "User");
ObjectSet result = db.queryByExample(user);
db.close();

2) In this second example, I create an ObjectServer and let the connection open for the whole lifecycle of the application. I also open ObjectContainer from the ObjectServer, make my query and then close it:

ObjectServer userDb = Db4oClientServer.openServer(Db4oClientServer.newServerConfiguration(), "User", 0);
ObjectContainer client = client = userDb.openClient();
ObjectSet result = client.queryByExample(user);
client.close();

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What are the main difference between both methods? Is it dangerous if I never close the ObjectServer?

In my opinion, the second method is better, because if two different instances call the method showed in the first example, the second caller will get an exception, cause the database would be locked, but in the second example I do not have such a problem. As I do not have much experience with db4o I prefer to ask if I am on the right way.