Probably important to notice: If you start a long query, then start something else, let's say the user manager, or click a table or a database in the tree, this is of course a problem as the server is not able to run parallel queries in one connection. Queries are run in a separate Windows thread, but do not mix up - they are runing in the same connection thread currently. Just had the idea of opening a new connection for each user query execution, which would heal this problem. On the other side this would break usage of cached objects, and session based variables etc., so that's not a good idea.