Blocks do not render, cpu hits ~100%

Firstly this problem happens with a map that I have generated through another program that I've written. There is the possibility that the problem is due to how I have written the region files and not a MC bug at all. However, given the behaviour, it could be a MC bug.

I have a map which is 100kmx100km (about 117 billions blocks in total). Regularly when I walk or teleport around the map, MC stops drawing blocks other than those a short distance around me. When this happens, the CPU usage rises to about 95%. the "pC" count on the debug screen rises up between 200 and 2000 and does not decrease again.

You can walk over the areas that haven't rendered and the terrain is the expected height. If you destroy a block near the un-rendered area then the blocks around it then get displayed.

If I generate a subsection of this map (10kmx10km), I still get the same problem but it seems to happen less frequently

I can only reproduce the problem in single player mode. If I run it on a server then it works ok, at least as far as my testing as gone.

The server logs do not report any errors.

If this was a problem with the way I'd written the region files then I would expect MC to fail on the same regions every time. Instead it fails in different areas at different times. I've tried various 3rd party programs to read the map (eg MCEdit, NBTExplorer) and they all read the maps without any problems. To me the problem looks like a timing/threading issue in the MC software.

To reproduce:

• Run MC in single user mode using the map. I've shared the map from Onedrive: https://onedrive.live.com/redir?resid=F7A10771AFD6ECB8!1714&authkey=!ANvR7CU3ggGc3vY&ithint=file%2czip

• Work around and teleport around until the blocks the "pC" count get won't drop to zero the blocks stop rendering. Some sample (x,z) coords for teleporting are (320326,248322), (329185,251007) and (332687, 252042)

• Try to save and quit the game, the regions seems to be saved successfully but it will hang.

I have attached screenshots of how it looks when it doesn't render properly and how another area looks when it is working.

(In case you're wondering, this is a 1:1 scale map of north east Scotland, to be extended to cover all of the UK if I can ever get this issue sorted out)