Chunk reverts to an earlier state

Can you attach a screenshot?

The first screenshot shows the chunk before i place the blocks.
The second screenshot shows the chunk after removing and placing some blocks.
The third screenshot shows the chunk after relogging in the world.

After the second log in in the world, theres a block update and the changes on the chunk disappear.

Is this singleplayer or multiplayer?

This is in my singleplayer world, which i created in the version 1.2.5.

Can you provide seed + coordinates?

The seed is -1063925407743966132

The coordinates are:
x: 428
y: 70
z: 316

Well I cannot seem to recreate this. Does this occur without any mods installed?

Yes, this appeared a few month ago and i just had installed optifine.
This appears everytime when i play this world.

Can you try this without optifine?

With a unmodded Minecraft.jar it is the same. I had already tried this. It was in every version i had updated to.

The error persists at any height in the chunk. I tried building on top of where I was getting the error initially, and the same happened. All of this with and unmodded Minecraft.jar.

How is the progress on this issue going on? I thought the past several snapshots would probably have it covered. Any news?

In snapshot 13w10a, it looks like this.If you try to fly trough it, you stuck in it. Minecarts can drive normally trough it.

The Minecarts, who are in this chunk, will double itselfs after relogging.
(you can see it on the new screenshot)

I've got this problem, too. A chunk where I built a staircase to traverse a cliff keeps reverting to an older state with a shoddy older staircase I built. Something strange used to happen, for a while, the old chunk (with the nice stone staircase) would flicker for a moment before going back to the old wooden shoddy one.

Please start Minecraft by

minecraft.bat

java -Xmx1g -Xms512M -cp minecraft.exe net.minecraft.LauncherFrame 1> log.txt 2> error.txt

and attach log.txt and error.txt after the error occured.

I´ve fixed my world a few days ago. I put my world into a Bukkitserver with the Worldedit plugin and marked the Chuck with the //wand tool. I made //expand vert, so that the whole Area is marked and i typed //regen and the chunk was regenerated. Since i´ve made this the Error is gone 😉

Seems like a very obnoxious bug. I have probably a couple of those phony chunks in my world.

Is this still a concern in the latest Minecraft version 14w05b? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

I have this problem in 14w05b but i am a noob! How do i update affected versions?

It is only my spawn chunk that is affected

affecting 14w06b

This is a video where you can clearly see what's is going on.The chunk recreate itself at each relog. I'm in the latest snapshot.

14w07a, bug still there...

14w08a sadly still have the bug. Is anybody taking care of the bug or I should restart a new world?

@Francisco, can you open your world, try interacting with this chunk, close your game, then do the following:
Please attach the complete output of the "Development console" which can be found on the second tab of the launcher.
If the launcher closes after game start, please edit your profile and select "Launcher visibility" then, "Keep the launcher open".

Yep, there you have the report.

I posted a duplicate of this (because I was specifically having problems with command block and didn't know it was a chunk error) This is on an adventure map I have been working on for ages, and the most recent bug fixes apparently caused all the chunks I have worked on to reload.... I am going to experiment with MCedit, but is there any thing I can do to save all of my bug fixes? If not I have a back up so that wont be a problem.... any help will be appreciated.

I can confirm that I have the same problem in my survival world.

Francisco Gimeno : Is your issue described in MC-18495 ?

I don't think so.

This is still occurring in the latest snapshots.

I have a potential cause, or at least a curious correlation. The chunk that I notice resetting in my SSP world happens to also be a slime chunk. Could someone else with this problem check and see if the affected chunks are slime-spawning chunks?

Hay mates! I noticed something really strange on the Defect chunk on my server. There is a Fletcher Villager with the following incompletable trade: Air + Air = Emerald. I'm putting a link to a video for more detail, in which I import it to single player and will do a bit of experimenting. Fingers crossed this at least helps! Link: https://www.youtube.com/watch?v=n83-Q-_g44E&feature=youtu.be

P.S.: BREAKTHROUGH! I FOUND THE CAUSE! Now that I've provided info for the it, the good gentlemen form mojang may have something to clink to. My guess is that it is an NBT error but let the experts say. HOPE THIS HELPS! Note: After the video ends and the villager is gone, all is normal. No chunk error, no crashes, propper chunk updates. Also, what I ment at the end is, if someone needs more info, or say mojang wants the world for closer inspection, then PM me. I will make a backup with the saves showed in this video (3 total: the gliched, the one where I kill the Villager and the one where he dissappears). Regards, Doomkaliber!

Interesting! I know that there is a broken Fisherman villager in the chunk I have problems with. I will try killing him. I know that the chunk duplicates mobs that were in the chunk in the previous state. I had a fletcher in that chunk, moved him, and now there's two of him. But when I moved one of my dogs into the chunk, the dog vanished upon reloading. So entities could be the source of the issue.

My real hope is that, as said, Mojang can somehow use the information I was able to provide (I think this is the first ever chunk issue solved) as a guidelight to the solution. (Looking at the kind gentlemen form Mojang) As I said, for any more info, that I can provide ofcourse, PM me on youtube, I check that most often.

added a logfile from today
with Version 1.7.10...
I also tried recreating the Map with the same seed and the chunk worked as it should, it seems the bug is not easily repeatable without the Mapfiles (~250mb in my case)...

oh right and in my 'failchunk' there isn't any generated Structure apart from Caves and an Abandoned Mineshaft, that stretches in the chunk from outside, that was also the cause for noticing the Bug.

it's impossible to play in that area of my game now because some things, like lava, torches, dogs and water, are refusing to update. just my luck that I have farms for several things in that chunk.
so yes, I believe that Entities are most likely suspect.
but it's hard to say whether defective entities cause the defective chunk, or it's the other way around. since the start of my game, I knew that there were defective entities, because my dogs would refuse to "get up" from their sitting positions.
there is no naturally generated structure in said failchunk, but there is a nether portal nearby, between two failed chunks, so I believe that chunk is suspect as well. i'm grateful that there's only one missing chunk in my world so far.

Ok, I have a suspicion. Both me and Etho had an identical issue, which was cased by villagers transferred form 1.7 to 1.8 snapshots. My suggestion is, check entities who's behavior/AI/visuals or whatever has been changed. Back up the world before doing anything. After backing the world just "/kill @e". See if issue persists. If not, reload the backup and start picking out the corrupting entities. If not, open another ticket with the same name to attract the attention of a developer, who will refer you to this issue. Note that in my case the corrupting entity was only one, where as in Etho's case it was two villagers in the chunk who were both causing the issue, which can tell us there can be multiple causes for chunk corruption. Hope this helps.

Is this still a concern in the current Minecraft version 1.8.1 Prerelease 3 / Launcher version 1.5.3 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.

I ran my old world which had this issue and it still persisted with the troublesome villager alive. As for whether it appears or not in a world where it previously wasn't a thing I'd suspect not as to my understanding it was caused by the villager transition form 1.7 to 1.8. Note that I am not backing up my suspicion nor my understanding of the matter with facts or code elements and may be completely in an opposite direction form the truth. I'm still too new to java to be able to inspect the code myself for such flaws. Yet I still keep the worlds archived and could easily send them to anyone willing to look into the matter.

Reopened, thanks

I'm having an issue where I use a command block to spawn a custom mob (a villager,) then I do something else where the chunk gets unloaded, and come back and the mob has vanished and the command block that I broke has returned. This happens on the same chunk every time.

I've been having issues with this in pretty much every world I have. Like Thomas said, I can confirm that after the chunk is defect for an unknown reason it may reset every time it is re-loaded. It reverts to it's previous state even though all other chunks surrounding it have maintained their latest data. My first guess of the cause was having a fast clock running somewhere in the world that would somehow delay chunk saves, but now I see that must not be the case.
I really hope this gets fixed, because it is not rare. It is a very big threat for both survival worlds and creative builds.

Can anyone confirm for 1.10.2 or attach a test world with coordinates?

Chunks reverting to an earlier state can be triggered reliably and I know one of the causes. I have just watched a Youtube video that demonstrates how to force a chunk to revert to an earlier state for the purpose of duping items. The video is here: https://www.youtube.com/watch?v=sd8SM8YWP9U

What's happening here is the chunk has too much data in it and Minecraft is refusing to save it. This is due to a known limitation of the Anvil file format.

The Anvil file format stores data for up to 1024 chunks in 4096-byte sectors that are the same size as a hard disk cluster. The first sector in the file is reserved for headers. Each chunk in the Anvil file has its own header which consists of a 24-bit offset to the chunk data and an 8-bit length in sectors. The chunk data is stored compressed in one of two different formats.

This 8-bit length is the limitation that can cause chunks to revert. This imposes a maximum chunk size of 1,044,480 bytes after compression. If a chunk is too large after compression, it cannot be saved, and it will revert to an earlier state.

As for the causes, I suspect there are several. Some of these have since been patched, such as slimes not despawning. Others still exist, such as entity duplication. Still others can be forced by players, especially in situations where players have some control over the NBT content.

1.13 has introduced another potential cause. The Flattening has introduced block palettes for each chunk section in the Anvil files. These can be space inefficient if each chunk section has 4096 different blocks (including block properties). This is unlikely to be a problem for block data in chunks, but this possibility should not be ignored.

The issue is going to keep happening randomly with different triggers until the real underlying cause of the issue is addressed. The limited size of chunks in the Anvil file format is one known cause as is demonstrated in the Youtube video. Expanding the Anvil file format so compressed chunks can be larger than 1,044,480 bytes is needed. One possibility is giving each chunk two 32-bit headers instead of one (32 bits for the length, 32 bits for the offset). The Anvil format was originally introduced when block data was only 12 bits and written books did not exist. Now that block data can be significantly larger, the Anvil file format is starting to show its age and some consideration should be given to replacing it.

I have attached a test world "ChunkRevert.zip" created with the instructions provided in the Youtube video: https://www.youtube.com/watch?v=sd8SM8YWP9U. Credit goes to the creators of this video and another linked video there.

In this test world, the chunk at spawn has been almost filled. In this chunk are two chests: a chest filled with two different written books arranged in a specific alternating checkerboard pattern. A second chest has the same written books in two stacks of 8. If these written books are arranged alternately in the second chest, the chunk will become too large to be saved and will revert when it is unloaded. The cause is almost certainly the Anvil file limitation I described in my previous comment.

Tested and is still a problem in 1.14.2.

I used a method detailed in https://www.youtube.com/watch?v=sd8SM8YWP9U

Possible fixes:

• Move the data for written books out of chunks and into a separate location, similar to how maps are handled.

• Reinterpret a length of 255 in the header to mean 255 or more. To find the actual length, query the first 4 bytes of the chunk data. The maximum chunk size will be increased to 2^31-1 which may cause its own problems (such as the file system being unable to handle many overlarge chunks in the Anvil file).

Still an issue on 1.14.3 pre 1, used the book duping method to reproduce this, note I didn't use the checkerboard pattern but instead used creative inventory to dupe a book 100 pages in size filled with random text and kept the duplicates to fill in 1x1 chest, as you can see from the logs, it surpassed the max allowed size which causes the exception and the revert

first exception is thrown for pressing esc (which saves the world on singleplayer), 2nd is thrown upon exiting the world, which again saves the world, while I don't know if there are any differences for these functions, I assumed it'll be best if both were logged

also note this behavior is similar in multiplayer, which makes this an exploit in many servers

14:25:29
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:the_end
14:25:29
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:overworld
14:25:29
r
Client thread
info
Loaded 143 advancements
14:25:30
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:the_nether
14:25:47
dxl
Server thread
info
Saving and pausing game...
14:25:47
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:the_end
14:25:47
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:overworld
14:25:47
us
Server thread
error
Failed to save chunk -8,20 java.lang.RuntimeException: Too big to save, 1363104 > 1048576 at bya.a(SourceFile:244) at bya$a.close(SourceFile:231) at java.util.zip.DeflaterOutputStream.close(DeflaterOutputStream.java:241) at java.io.FilterOutputStream.close(FilterOutputStream.java:159) at java.io.FilterOutputStream.close(FilterOutputStream.java:159) at byb.a(SourceFile:61) at bxy.a(SourceFile:58) at us.a(SourceFile:695) at us.e(SourceFile:371) at us$$Lambda$2976/1348121416.accept(Unknown Source) at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184) at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175) at java.util.Iterator.forEachRemaining(Iterator.java:116) at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Spliterators.java:1801) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502) at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418) at us.a(SourceFile:368) at ve.a(SourceFile:282) at vg.a(SourceFile:741) at net.minecraft.server.MinecraftServer.a(SourceFile:529) at dxl.a(SourceFile:120) at net.minecraft.server.MinecraftServer.run(SourceFile:632) at java.lang.Thread.run(Thread.java:745)
14:25:47
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:the_nether
14:25:48
vy
Server thread
info
KillA2k18 lost connection: Disconnected
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
KillA2k18 left the game
14:25:48
vy
Server thread
info
Stopping singleplayer server as player logged out
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
Stopping server
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
Saving players
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
Saving worlds
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:the_end
14:25:48
us
Server thread
info
ThreadedAnvilChunkStorage (DIM1): All chunks are saved
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:overworld
14:25:48
us
Server thread
error
Failed to save chunk -8,20 java.lang.RuntimeException: Too big to save, 1363104 > 1048576 at bya.a(SourceFile:244) at bya$a.close(SourceFile:231) at java.util.zip.DeflaterOutputStream.close(DeflaterOutputStream.java:241) at java.io.FilterOutputStream.close(FilterOutputStream.java:159) at java.io.FilterOutputStream.close(FilterOutputStream.java:159) at byb.a(SourceFile:61) at bxy.a(SourceFile:58) at us.a(SourceFile:695) at us$$Lambda$3125/1876601227.test(Unknown Source) at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:174) at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175) at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374) at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:512) at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:502) at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151) at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174) at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418) at us.a(SourceFile:358) at ve.a(SourceFile:282) at vg.a(SourceFile:741) at net.minecraft.server.MinecraftServer.a(SourceFile:529) at net.minecraft.server.MinecraftServer.l(SourceFile:564) at dxl.l(SourceFile:251) at net.minecraft.server.MinecraftServer.run(SourceFile:666) at java.lang.Thread.run(Thread.java:745)
14:25:48
us
Server thread
info
ThreadedAnvilChunkStorage (New World (2)): All chunks are saved
14:25:48
net.minecraft.server.MinecraftServer
Server thread
info
Saving chunks for level 'New World'/minecraft:the_nether
14:25:48
us
Server thread
info
ThreadedAnvilChunkStorage (DIM-1): All chunks are saved

Can this be reproduced in the latest snapshots (currently 19w37a)? There have been various fixes in regards to word saving and chunk storage.

This report is currently missing crucial information. Please take a look at the other comments to find out what we are looking for.
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