1. Optimize Region File Cache (commit: 1571211) (details)
Commit 15712119ad2f47608105e9f13b669393b4f45972 by aikar
Optimize Region File Cache
CraftBukkit added synchronization to read and write methods. This adds
much more contention on this object for accessing region files, as the
entire read and write of NBT data is now a blocking operation.
This causes issues when something then simply needs to check if a chunk
exists on the main thread, causing a block...
However, this synchronization was unnecessary, because there is already
enough synchronization done to keep things safe
1) Obtaining a Region File: Those methods are still static synchronized.
  Meaning we can safely obtain a Region File concurrently.
2) RegionFile data access: Methods reading and manipulating data from
  a region file are also marked synchronized, ensuring that no 2
  are reading or writing data at the same time.
3) Checking a region file for chunkExists: getOffset is also
  ensuring that even if a chunk is currently being written, it will be
By removing these synchronizations, we reduce the locking to only when
data is being write or read.
GZIP compression and NBT Buffer creation will no longer be part of the
synchronized context, reducing lock times.
Ultimately: This brings us back to Vanilla, which has had no indication
of region file loss.
(commit: 1571211)
The file was addedSpigot-Server-Patches/0359-Optimize-Region-File-Cache.patch