the game fills allocated memory, freezes for approx. 1 second, then jumps back to normal levels of memory usage. then the memory allocation starts going up again for 1-3 seconds (I think depending on how much memory is being used to render) and the process repeats. during the time frozen the display is frozen and the game does not accept inputs, but the world still runs (gravity and mobs still are simulated) this is extremely annoying when you are trying to go up hills and makes the game hard to play. This does not appear to happen on multiplayer servers.