In early 1.9.4 spigot builds the chunks would just go up to 20 k and stay very high. But in git-Spigot-8a048fe-d8637df (built with buildtools on 2016-05-20) there seems to be some new cleanup mechanism which still has the behaviour of the chunks loading very fast but it seems to have some cleanup triggered so now and then which makes the chunk count lower but then rise again. And this very fast chunk loading and unloading causes a lot of cpu load (and the chunk count is still 4-5 times higher compared to spigot 1.8.8.)
I have set up a system that logs the loaded chunks and loaded living entities and dead entities into graphs. I have used spigot for 3 years now and i was always impressed on how low it could keep the chunk and consequenctly the living and dead entities counts. 1.8.8 was perfect in this regard but when i updated to 1.9 the issues began.
I have included a graph with the counts. might help to see some patterns in the changed chunk loading behaviour
Expected: When 2 players are on the server only the spawn chunks and the chunks around the players are loaded. about 2 k chunks and not 10 or 20 k.