Now, after did /spark heapdump I have a bigger problem. Very big. When I start the server with xms set to 4GB the server on idle with 0 players take 12GB RAM! I noticed that the ram grows very fast from 4 to 12GB when the worlds are loading. I deleted plugin Multiverse-Core and problem dissapeared but this plugin is most important for me. I dont know why this happened. Before /spark heapdump everything was OK and server on idle take only XMS value (4GB) (I checked it by htop on ubuntu). Now server takes 12GB on idle and turns on about 20secs! Before spark heapdump it was take to turn on about 9 - 11 secs..