Block ID mapping was destroyed -- world corrupted. in Support & Bug Reports Posted October 26, 2014 This happened with Forge 1208. I am aware that this is not latest. This is not repeatable reliably -- I have run this same setup many times without problems, and do not know why it decided to die on me now. EDIT: Potentially, the crash happened in single player when the client ran out of memory. Again: My block/item ID mapping was wiped. All ID numbers in the region files were claimed by a different block, so anything not vanilla became something else. Opening a chest resulted in a client D/C. Restoring a copy of level.dat from a backup did recover blocks properly (* but NOT their orientations *) in the overworld and most ages, but the most recently used mystcraft age had horrific wrong blocks. This is sufficiently catastrophic (loss of ID map destroying everything) that I felt it should be reported even though it's not latest. Logs: First, starting up the world in SMP mode. No problems -- everything worked just fine. https://gist.github.com/keybounce/b77dc5f2f2cf893fb694 Then, I realized that I was planning on doing long-term chunk profiling -- and trying to run my client by itself will result in a random d/c after somewhere from 30 minutes to 2 hours. (This happens when minecraft falls 25-30 seconds or more behind, and skips ticks to catch up -- the client complains, D/C's, and on reconnect the player's position is far, far away from any place the minimapper remembers getting data for from the server. I don't think this is a forge error; I think this is just chunk generation slowness.) So, I stopped the server, and restarted in single player. Startup was no problem. Logs: https://gist.github.com/keybounce/8525a6c45859329fb3ea Again, at this point, no problem. So now, I start up again, set flight mode, fly off in a diagonal, and plan to come back in the morning with many hundreds of thousands of chunks profiled overnight while I slept. After about 30 minutes, the client ran out of memory, and shut down. https://gist.github.com/keybounce/f448ecb8e9494ee80e36 The crash happened at 1 am. level.dat from that timestamp has a broken set of ID mappings in it. level.dat from 11:58 pm the previous day has proper ID mappings. (no copy between those two timestamps is available) ... reviewing that log, I had been under manual control until about 12:40 am, put it on auto-pilot at that point, and it ran out of memory 20 minutes later. Again: At this point, the level.dat saved and in Time Machine shows a broken set of block ID mappings, while the one from the previous night just before midnight has a good set of block ID mappings. World sharing: The client has a symbolic link from the save directory into the server's directory. Other than getting a different inventory/location when logging in single player than server, everything works fine in both setups.