MC-177542Chunk loading and saving is extremely slow when sync-chunk-writes=true
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.
Update: I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes. Other users have reported this issue to occur on Windows; the severity of this issue may be setup-dependent.
Update 2: Attempted running 20w15a on Linux with Oracle Java (1.8.0_241 64-bit) instead of OpenJDK, issue persists.
Environment
OS: Kubuntu 18.04 64-bit
Linux 4.15.0-46-generic
Java: OpenJDK 1.8.0_242 64-bit
Linked Issues
Created Issue:
World generation and saving is extremely slow
Starting in 20w14a, world generation seems to have taken a massive performance hit. Generating new chunks is much slower than usual, to the point even gliding with elytra in singleplayer has me floating over a void for a good 15 seconds. Saving and returning to the main menu is also around ~10-20 times slower than in 20w13b (and even 20w14∞), often hanging in the "Saving world" screen for over a minute after generating a fairly modest amount of chunks.
How to reproduce
- Create a new world
- Equip elytra and fly away in any direction
- Admire the emptiness
- After the chunks finish generating, save and quit to title
- Grab some popcorn and enjoy the "Saving world" screen
I've attached a video of the above, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
Environment
OS: Kubuntu 18.04 64-bit
Linux 4.15.0-46-generic
Java: OpenJDK 1.8.0_242 64-bit
Attachments3
World generationand saving is extremely slowChunk loading and saving is extremely slow when sync-chunk-writes=true
Starting in 20w14a, world generation seems to have taken a massive performance hit. Generating new chunks is much slower than usual, to the point even gliding with elytra in singleplayer has me floating over a void for a good 15 seconds. Saving and returning to the main menu is also around ~10-20 times slower than in 20w13b (and even 20w14∞), often hanging in the "Saving world" screen for over a minute after generating a fairly modest amount of chunks.
How to reproduce
- Create a new world
- Equip elytra and fly away in any direction
- Admire the emptiness
- After the chunks finish generating, save and quit to title
- Grab some popcorn and enjoy the "Saving world" screen
I've attached a video
of the above, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.
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The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.I've attempted to reproduce this on Windows (64-bit)
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.I've attempted to reproduce this on Windows (64-bit)
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with drivers
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between OSes
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes.
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.Update: I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes.
Update 2: Attempted running Minecraft on Linux with Oracle Java (1.8.0_241 64-bit) instead of OpenJDK, issue persists.
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.Update: I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes.
Update 2: Attempted running
Minecrafton Linux with Oracle Java (1.8.0_241 64-bit) instead of OpenJDK, issue persists.The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.Update: I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes.
Update 2: Attempted running 20w15a on Linux with Oracle Java (1.8.0_241 64-bit) instead of OpenJDK, issue persists.
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The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.Update: I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes.
Update 2: Attempted running 20w15a on Linux with Oracle Java (1.8.0_241 64-bit) instead of OpenJDK, issue persists.
The sync-chunk-writes server option added in 20w14a, when enabled, causes massive server lag when loading and saving chunks; both in singleplayer and multiplayer. This is most easily noticed when generating new terrain and traveling through portals, and is so severe that merely flying with elytra through new chunks easily brings the server to a halt, leaving the player suspended over a void while the chunks are being generated. Saving chunks also takes much longer (~10-20 times slower) and causes lengthy loading screens when e.g. changing dimensions or returning to the main menu.
Choice of storage medium has an effect; worlds stored in faster media, such as SSDs, experience less severe (but still very noticeable) effects than those in slower media, such as HDDs. Overall, opening region files in synchronous mode seems to limit the game speed more directly to the (slower) underlying disk speed.
This option is enabled by default and cannot be changed in singleplayer, rendering the game nearly unplayable when traveling long distances. Disabling it in a dedicated server by setting sync-chunk-writes to false in server.properties resolves the issue.
I've attached a video demonstrating the issue in singleplayer, a corresponding server log excerpt (notice the "Can't keep up!" messages and the time gap between "Saving chunks for level" and "All chunks are saved"), and a crash report from holding F3+C while flying over the unloaded chunks.
I have only tested this on Linux (Ubuntu), need confirmation on other OSes.Update:
I've attempted to reproduce this on Windows (64-bit, Java 1.8.0_51), but it does not seem to occur. Saving does still take slightly longer, but it's not much of an issue. This might have to do with driver differences between the two OSes.Other users have reported this issue to occur on Windows; the severity of this issue may be setup-dependent.Update 2: Attempted running 20w15a on Linux with Oracle Java (1.8.0_241 64-bit) instead of OpenJDK, issue persists.
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This also happens in minecraft bedrock. In my phone
Maybe cause by this bug:
Does setting "sync-chunk-writes" to false increase the chunk loading performance? If so, see MC-177542.
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Resolved as a duplicate of MC-177542.
Does MC-177542 explain your issue?
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Thank you for your report!
However, we are already tracking this issue, and this report is a Duplicate of MC-177542.
Please use the search function in the future to prevent duplicate reports.
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If you have this issue – please check whether sync-chunk-writes is disabled or enabled. If you're on linux, try disabling it and check if it's better. Linux is known to not handle sync chunk writes very efficiently, see MC-177542.
I have launched a dedicated Minecraft Java Edition 1.20 server for a couple of friends on an Ubuntu machine. As the server grew the autosave time has become increasingly longer to the point when the game became unplayable. Disabling the autosave and saving with /save-all every hour or so helps, but at this point saving the world takes longer than 9 seconds (judging by the "Can't keep up" message that pops up after each save).
This time does not seem to be affected by anything that is currently happening in the world, including when no one is logged in. The server has several datapacks and fabric mods on it (which do not require client to use any mod loader), but the issue is precisely reproduced on the purely vanilla copy on 1.20.1, just with same world directory (including the datapacks, I forgot to remove them when testing).
The issue also appears to be directly tied to the size of world directory, because a new world with a lot of pregenerated chunks weighs next to nothing and does not experience same issues, but my main world directory weighs more than 9GB already. All of this suggests that autosaves save all chunks, regardless of whether they were changed or not, but this seems unreasonable.
An extensive search for a complaint about a similar issue has led me to MC-177542, but setting sync-chunk-writes=false did not help at all. Strangely, I did not find any other similar complaints about this topic, although it seems to be a particularly widespread issue if we assume that all it takes to reproduce is just a large minecraft world.
This happens to me too. It says in f3 debug mode that my game ticks running with 5-20 ms but I opened my task manager and it using 100 % of my harddrive. In the latest snapshot it is impossible to fly with elytra.
I'm on windows 10.
CPU: Intel(R) Core(TM) i5-4570 @ 3.20 GHz
GPU: GeForce GTX 1050 ti
Ram: 8 GB
For anyone voting, can you put information about your setup here? (mostly interested in OS and if it's SSD or spinning drive)
I have a HDD. TOSHIBA HDWD110.
Windows 10 pro.
Manjaro Linux 20.0.1 on a Schenker XMG A507-vsy, Minecraft data is on the HDD.
I just tested it with the SSD and it seems to be much better there (of course, SSDs are faster), but still noticeably slower than in past versions at least sometimes. When using the SSD, Minecraft does not appear with "100%" in the output of "iotop", which it does for minutes on the HDD.
Kubuntu Linux 18.04.1, Minecraft is on HDD (Seagate ST1000DM010-2EP102, 1TB, 7200RPM, 64MB cache)
Debian 8.10 (way old, I know
) and spinning HDD. Chunk loading can't keep up with elytra anymore.
Edit: I'd be happy if there was just a way to turn this feature off for singleplayer mode.
I experience this on the latest snapshot (20w22a), both on HDD and NVME SSD. Granted, on the SSD, the saving time is much lower (about 3 seconds), whereas on the HDD it is about 10-15 seconds.
I am on Arch Linux, 5.6.14-arch1-1 kernel.
This is my experience on this bug:
https://drive.google.com/file/d/1ny1qxYzQeT315XRoa1kRTr35cqt4xXsM/view?usp=sharing
And when the chunks are loading the whole world freezes.
May I know what the solution was to this?
When sync-chunk-writes=true, (for java dedicated server) it still causes a large amount of IO usage, slowing down chunk generation and overall server performance in proportion to the speed of the disk drive.
Was the solution just to set sync-chunk-writes to false ?
Yes, the solution is to set sync-chunk-writes to false.
Rapidly flushing in-mem data naturally always comes with a performance hit. Depending on how how severe this affects you, you should indeed disable this option.
Im sorry, maybe i dont understand this. After running timings i see to be having the same issue, where can i edit that setting in my Minecraft server? Thanks!
Gaston Vionnet, as per the ticket description, you have to set sync-chunk-writes=false in your server.properties file.
I know, this is gonna sound stupid, sorry in advance. But what if, there´s no Config like it in the server.properties? Should i write it down myself or am i doing something wrong?
Yes that's right, just add it yourself.
Did this regress?
I just pulled server.jar version 1.16.2[1], running it in an otherwise empty directory, and `sync-chunk-writes` defaulted to `true` when running on Arch. Performance matched descriptions here. A naive reading of the documentation following 1.16 PR3 would suggest that `sync-chunk-writes` would default to false under this scenario, given the platform was not Windows.
[1] (sha256: 2902ed3ff84e4f810a2c0620c6b6df9c3ef8488b272c61274d5eac2433876f39)
I think this is still an issue. At least in singleplayer. Saving worlds in 1.16.5 (and 1.17 snapshots) always takes minutes, but in 1.15.2 it took less than a second for me. I think this should be reopened.
I was having the exact same problem in 1.17.1. I was very confused why my server was lagging so much when players were exploring new chunks. When I found out it was due to this setting I was very surprised.
Like the opener of this issue stated this is terrible for world files stored on HDD's because HDD's aren't well-suited for random IO. Using the DSYNC option for file I/O doesn't give the OS a chance to coalesce these writes resulting in 100% disk activity at a puny write speed of around 700KB/s. While the disk is busy writing at those slow speeds the server is waiting for the write call to complete. With sync-chunk-writes set to false the disk is active for very short periods of time writing at several megabytes per second.
As expected moving the world files over to an SSD alleviates the issue somewhat.
https://www.minecraft.net/en-us/article/minecraft-snapshot-20w14a
The original motivation for this change was that it should prevent data loss or corruptions in the case of a crash. I don't think this is a good argument. As soon as the write system call has completed it's the operating system's job to commit the changes to disk at it's discretion. By default the linux kernel flushes queued data every 5 seconds, or when free memory goes below a certain limit. The only reason that the operating system wouldn't get the chance to commit to disk is when the entire system goes down unexpectedly (like power outages) in which case all bets are off in terms of data integrity anyway.
https://old.reddit.com/r/admincraft/comments/hn0g84/syncchunkwrites_causing_lag/
There are more people who complained about this and it seems that unofficial servers like paper ignore the sync-chunk-writes property and hide it as a command line flag instead.
For those reasons I think this issue should be reopened.
goeiecool9999, this bug report is mostly about the issue affecting users in single-player, since it is only a setting in multi-player. The reason it is enabled for the purpose of preventing data loss is for Windows users specifically, and as such it is not enabled by default (again, in single-player) on Linux. The ability to change the default setting is the easy solution to not experience this problem on Linux servers.
For any additional discussions about bug reports, please take them onto our subreddit.
This could also be fully fixed by writing chunks to regions in batches instead of one by one, which I have implemented as a proof of concept mod (is it ok to link the code here?), while keeping the safety properties regarding data loss. It makes a huge difference with an HDD, time to save the world can go down from minutes down to the normal few seconds. This would likely also benefit servers, as it would allow to actually use that option without being forced to have an SSD.