I’ve previously covered fixing Valheim’s dedicated server lag by modifying the dedicated server’s send receive limits. Since I wrote that article not long after launch though the game has been updated that the old method no longer applies. I had theorized in the comments of that article how to address this and today Sam R. confirmed that this method did indeed alleviate most congestion on the server in the places that the send/receive limits are known to bottleneck.
This updated guide will show some updated methods you can use to help reduce lag on your Valheim dedicated server!
Symptoms of lag on Valheim dedicated servers
The symptoms you are experiencing on the server can help narrow down what type of lag you are experiencing and what may be causing it. Lag caused by your CPU being too overloaded for example will have different symptoms than lag that is caused by your server hitting the maximum send/receive limit as an example.
By far the most common type of dedicated server lag seen in the early access Valheim release so far has been mainly due to the low send/receive limit if 64KB/s that is hard coded into the server. This means that when you do something like take your character a heavily populated area on the server it has to send all that information about all the buildings/players through an artificially limited very narrow 64KB/s pipe.
Symptoms of the send/receive limit type of lag include things like chests taking a very long time to open, sometimes 10-30 seconds or never opening while at the same time being able to see players walking around normally. This is because the other people’s X / Y / Z positions is a very small amount of data compared to all the items/names/attributes that are stored in the chest. The other players moving easily fits through the narrow pipe while the chest full of loot’s data chokes since it is much larger.
I’ll specifically lay out how to modify your server and increase this limit in the “Modifying your server’s send/receive limit” section below. Before that though let’s cover a more specific type of lag to watch out for (mostly by being avoided) related to terrain manipulation.
Avoid extensive terrain manipulation (for now)
Another commonly observed source of lag has to do with terrain manipulation. Some players have found that if they take a big chunk out of the ground in Valheim and make extensive terrain modifications that the area gets filled with separate “instances” of terrain for each modification people make. Think of the original ground as one big piece in the game files. Valheim has the very cool feature of letting you modify terrain by raising it/lower it/level it/etc. Each time you do this though the game has to store what you did as a new “instance” or a modification.
The way Valheim seems to work now is it renders that original piece and then the modifications afterward. Early reports suggest having a whole bunch of them in one spot seems to sometimes cause everyone’s in-game FPS on the server to drop as low as 40 when the clients normally are much much higher than that.
The best way to avoid this type of lag at the moment is to limit how much terrain modification you are doing in areas near your base. It is likely this will be addressed/eased in future patches. There should be some things the developer team can do to clean up/merge these instances or at least reduce their effect on the rendering process so it doesn’t drop the in-game FPS so dramatically.
Prebuilt Binaries Links (Added 1/10/2023)
Sketaful has volunteered to put together binaries of the modification in this article.
His file repository is located here.
Thank you for doing this Sketaful for as long as you are able. If the files are no longer working let me know in the comments and I’ll remove the link but as long as Sketaful wants to compile the binaries I’ll link to them here!
If you want to use Sketaful’s binaries you can skip way down to the “Backing up original file and replacing with our new one” section. That will tell you where this file needs to go and let you safely back up your original one first.
Modifying your server’s send/receive limit
At this time there is no options file for Valheim unfortunately. The only way to change it is to modify the server’s code and recompile the module that controls this.
Fortunately this is a lot easier than it sounds because the module we need to change is in .NET instead of something like C++ which would be much more difficult to do this with. I did not come up with this method, a very clever user on reddit (maximgame) shared it here and I want to give credit where credit is due!
Despite it not being too difficult these modifications are at your own risk. I haven’t experienced any problems so far but technically we are modifying the server’s code with the following procedure so understand that this isn’t an officially supported method and could have side effects or if you make a mistake could cause serious problems. Make sure you have backed up everything (your game world files especially) before you try anything!
Another important note is that it’s very likely you will have to make the changes again each update since the file we are going to modify is going to get replaced by updates. Until they add either a launch option or options file to officially change/control this property that is unfortunately unavoidable.
With all that being said if you understand the above and still feel comfortable let’s proceed!
Get dnSpy utility
We are going to use the utility dnSpy to modify the server code and recompile the module. The utility is free and is available here (download the Win64 build or dnSpy-net-win64.zip): GitHub dnSpy Official Page
Extract the archive and run the program dnSpy.exe from inside the folder you extracted. The dnSpy application will open.
Modifying server with dnSpy
We are going to go to the “File” menu in the top left and choose “Open” like this:
Now you need to navigate to the Valheim dedicated server folder which is located in your “steamapps” folder. If you left all the options default when you installed it’s typically “C:\Program Files (x86)\Steam\steamapps\common\Valheim dedicated server\valheim_server_Data\Managed”.
We are looking for the file “assembly_valheim.dll” in that folder:
Select the file “assembly_valheim.dll” and click “Open” and the server’s assembly will load into dnSpy.
Once it has finished loading we are going to go to the “Edit” menu and click “Search Assemblies” like this:
For the search criteria enter “ZDOMan” like this:
After the search completes you should see a list of results like the one above. Double click on one of these entries on the list and it should place you in the ZDOMan section of the assembly (seen on the left hand side of the screen):
Perfect. We are now in the right place to make the changes. We just need to locate the line that has the send/receive limitation. To find that press Ctrl+F to bring up the find box (or choose “Edit” -> Find from the menu) and search for:
which should bring up the following lines:
If you are having trouble finding the lines make sure you’re using Ctrl+F to search this time and not the “Search Assemblies” from earlier at the bottom of the screenshot, that’s a different type of search. Make sure you’ve disabled the case sensitive options (the Aa right below the box) or any other search filters. Your search query box should be in the top right of the screen like the above screenshot that has sendQueueSize in it.
Now right click on this line:
int num = 10240 - sendQueueSize
and click “Edit Class (C#)…”. Another window will open that will let you make changes to the file. We are going to modify ‘10240’ to a variable of our choosing. I made mine 30720 since after doing some conversion math that is the equivalent increase from my previous launch version guide that provided great performance and I kept them the same. If you followed my last guide this will give you the exact same performance as the old one did.
There are two instances of this variable. The second instance is 3 lines above the highlighted line we searched for and is:
if (!flush && sendQueueSize > 10240)
Modify both instances of 10240 to 30720.
Theoretically setting a limit too high could cause the server to swamp your internet connection if you have a large number of players on and there’s essentially no limit but there shouldn’t be any other effects of a very high number.
Once you’ve changed both numbers to the desired value we need to press the “Compile” button in the bottom right corner of this new window. This window will close and take you back to the previous one.
Saving the new assembly
It’s time to save our changes into a new .dll file. Choose “File” -> “Save Module…”:
Change the file name to assembly_valheim_modded.dll. Don’t overwrite the original file just yet as we will want to take a backup and make sure that the server is closed before we do that. Press “OK” to write the new assembly_valheim_modded.dll file.
Backing up original file and replacing with our new one
Now it’s time to back up the original file and replace it with our new modded file. First make sure your dedicated server is closed otherwise the dll file will be in use. It is also a good time to make a backup of your world file just in case (see my Valheim Dedicated Server Backup Location / Guide for instructions)
Navigate in a file explorer window to your Valheim server directory where we saved the new assembly file (usually C:\Program Files (x86)\Steam\steamapps\common\Valheim dedicated server\valheim_server_Data\Managed).
First make a copy of the original assembly_valheim.dll file. You can just select the file and “copy” then paste a copy of it in that same folder and Windows will make a “valheim_assembly Copy(1).dll” file for you or you can back it up to a separate folder. Now remove the original file and rename your “valheim_assembly_modded.dll” file to the original file name of “valheim_assembly.dll”.
That’s it, you’ve now replaced the old assembly with the new one! Go ahead and start your server normally and the changes will have taken effect.
Make sure you are taking constant backups of your Valheim dedicated server: Backup Valheim Dedicated Server – World Folder Paths / Guide
It’s also important to back up your local game’s characters and local worlds if you are using them. I have written a guide for the local game side that is available here!
For historical reasons I’ve left up the post with the old method here as it helped me devise the new method: Fixing Valheim’s dedicated server lag by modifying the dedicated server’s send receive limits
Other Valheim Lag Issues
If you know of other Valheim lag issues that I didn’t cover here or are still having problems let me know in the comments and I will update this guide with other tips/tricks and try to answer any questions. It’s still a very new game and there isn’t very much out there for it yet. Have fun and enjoy!
Came across this article after I had already invited 8 or so of my friends to my shiny new self-hosted server before realizing Valheim’s capacity shortcomings. While imperfect, this mod DOES help a bit with the rubberbanding and general lag with so many online, I think maybe we might just have to deal with ‘acceptable’ at this point.
Though something I did notice, is even after applying this modification and verifying that it did produce good results with about 5 people, once we got to around 8 people online, it looked like our send and receive speeds kept dipping below 30 and the lag started to come back. Is this normal for a larger set of players? Is the rate distributed amongst people in the server?
Thank you so much for this helpful writeup and the work you’ve done!
Thank you so much for your kind words here, and you are most welcome! So I think what you are describing is about right. This mod buys you about 1 additional player slot before the problem starts.
It gets worse every update. If you read through the comments here this is a pretty universal sentiment. At launch this mod would probably get you up to 6 roughly. It’s probably about 5 now. Without it it starts lagging at 3-4.
The reason for this is that each update they add new features and data. For example this update has a new stat (Eitr or basically mana/magic). That’s all additional data that is being sent around that didn’t exist at launch. This system was already woefully inadequate at launch but it was less taxed than it is now after all of the updates.
In other words this workaround is basically like using a band-aid to close up a wound that actually needs several stitches. It’s not going to be enough. The Valheim developers need to go in there and do some serious operating and then stitch the patient back up. That’s not going to happen though. It has been this way since launch and it has only got worse unfortunately.
I gave up hope for them fixing this a long, long time ago. I’m not sure they’re even capable of it or that they even understand the problem. If it’s ever fixed it will be via player mods that completely throw out Valheim’s networking code. It has to literally be the worst multiplayer code ever released rivaling like old original Xbox games that were purely P2P.
It’s actually worse than those old Xbox P2P games because Valheim uses a bastardized mix of P2P and standard client/server multiplayer models that literally make no logical sense. Instead of the advantages of one or the other since they mixed them it has the disadvantages of both.
It’s like mixing a bunch of flavors together at the soda fountain. If the flavors aren’t complimentary such as lemon lime with a specific other compatible soda (and most of them won’t be) the taste you get will *not* be better. Most of them will clash and be *nasty* and that is exactly how I would describe Valheim’s networking code and how they mix multiplayer models. You end up with the disadvantages of each multiplayer model and there ends up being no advantage. They’re behaving like children trying to mix a bunch of soda flavors together with absolutely no understanding of which flavors can go together thinking it’s going to end up awesome with superpowers from all the different flavors. Then it turns out super nasty which any adult that has the slightest clue what they’re doing could have told them. That’s how I see them.
Hopefully that helps!