Commit c576054539790bdeb35285f62863d74b48c0782d removed the chunklist collection stored in ChunkProviderServer, however it has been partially restored in some places by 7e1ac0a77129b169704c1e222ff2deb3ab6cd2d2. As not all references to this were restored, this has caused the chunklist and chunks collections to become out of sync, resulting in a memory leak.
There is very little reason to keep track of Mineshafts as the only persistent behaviour within them is through the use of mob spawners, which are of course stored within the map itself. As such we can disable them from being saved, indefinitely, until there is reason to do so.
This brings back the option that the Spigot version of netty saw. By default Netty will try and use cores*2 threads, however if running multiple servers on the same machine, this can be too many threads. Additionally some people have 16 core servers. If 32 Netty threads are allowed in this setup, then the lock contention, and thus blocking between threads becomes much greater, leading to decreased performance.
Useful for larger servers who want a nice performance boost at the expense of a little bit of gameplay mechanic changes. I believe this brings the mechanics of zombie vs villager back in line with 1.5.
Now we maintain a new list of blocks to replace with ores in engine mode 2, to ensure that we only update when players mine blocks that are potentially not an ore. We could perhaps even elimate this slight lag from mode 2 by reducing the need for calling update(x,y,z)
As of 1.7, Mojang added a check to make sure that only chunks which have been lit are sent to the client. Unfortunately this interferes with our modified chunk ticking algorithm, which will only tick chunks distant from the player on a very infrequent basis. We cannot unfortunately do this lighting stage during chunk gen as it appears to put a lot more noticeable load on the server, than when it is done at play time. For now at least we will simply send all chunks, in accordance with pre 1.7 behaviour.
