Other folks have answered. I'll try to summarize: It's an impedance mismatch, you have a long-running background operation (sql query) that is running within t

Other folks have answered. I'll try to summarize: It's an impedance mismatch, you have a long-running background operation (sql query) that is running within the context of an event driven system (a windowing GUI). In this case the problem is that the sub-system that runs the query will only receive cycles when the main thread for the app fires mouse events. This is due to poor application design, of course, though not necessarily to the extent that it may seem, sometimes this sort of thing can be a harder problem than it may seem.