Revisiting Fixing Valheim Lag – Modifying Send/Receive Limits

My Valheim Dedicated Server Castle
My Valheim Dedicated Server Castle

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.

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 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:

dnSpy - File -> Open Menu
dnSpy – File -> Open Menu

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:

dnSpy - Select File
dnSpy – Selecting Valheim server assembly file

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:

dnSpy - Search Assemblies
dnSpy – Search Assemblies

For the search criteria enter “ZDOMan” like this:

dnSpy - ZDOMan Search
dnSpy – Searching for ‘ZDOMan’

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):

dnSpy - 'ZDOMan' section of assembly
dnSpy – ‘ZDOMan’ section of assembly

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:

dnSpy - sendQueueSize Variable
dnSpy – sendQueueSize Variable

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…”:

Saving New Assembly
dnSpy – Save Module as assembly_valheim_modded.dll

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.

Other Resources

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!

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11 days ago

We got a Massive improvement using this fix when we got to the ashlands and the mobs where desyncing all over the place, the players with weaker hardware had to do it on their own machines aswell but other than that it works great

1 month ago

When I try to decompile it gives an error:
Severity Code Description File String
Error CS0518 Predefined type ‘System.Single’ is not defined or not imported main.g.cs 440
Severity Code Description File String
Error CS1069 Could not find name of type ‘List’ in namespace ‘System.Collections.Generic’. This type was submitted to assembly “System.Private.CoreLib, Version=, Culture=neutral, PublicKeyToken=7cec85d7bea7798e”. Try adding a link to this assembly. main.g.cs 467

4 months ago

anything we can do to help FPS drops in base? i see 10000+ instances being generated when pressing F2.

such as would chopping all nearby trees next to base increase FPS/reduce lag?


28 days ago
Reply to  lex

If you’ve generated your world long time ago, (before april 2022 i think), and did lot of terrain modifications. You can use the “optterrain” in-game command. But first, I recommend you to make a backup of your worldmap. The principle of this command is to migrate old terrain code to more new efficient terrain code on certain radius arround you character. Since april 2022, an update optimize terrain modifications.
There is another ingame command, that “maybe” will help you to improve perfromances. With cheat codes enabled, type in “removedrops” into the console. Doing so will remove all items dropped on the ground in the worldmap.

4 months ago

Has there been an update, because when going into one of my portals I saw, data recv: hit 124kb, I have not modded or done anything to the base game.

4 months ago

Update… I realized after your specific words in a response to another post. In the “compiler window” search Ctrl +F , then the replace all command was available. Changes were compiled and saved. Launched local dedicated headless server without issue. Loaded the game into the server no issues. Although need to wait for my buddies later to test for their gameplay. I have done the decompiling and editing of the client DLL as well but have not applied it yet to the client files as there is no mention anywhere about the client side aspect or whether the other clients joining the server need the client side dll modification as well ?

However being both locally hosted on the same pc I didn’t expect results of the data transmission edit for myself but was hoping. Just started playing the game on December 22nd via steam. Amazing game and loved it !! High FPS 140-150’s …looked and felt great! However noticing after a while of gameplay with 2 other friends in this dedicated private public server. We started to notice severe lag at our home base that I mostly developed in debug. With that I did severe Terraforming across from our landed base. Built up a huge area of land to create a natural wall, and the ability to dig a deeper basement tunnel system. After a while started to notice that my video card wasn’t even pushing the game anymore (RTX306012GB) thought it was weird and noticed our home base was giving me around 20-30fps.. sometimes less than 20. I tried drivers, video card, load treating … everything ! Now reading about unity engine games and terrain modifications or terraforming is a big NoNo in Valheim or Unity Engine games. However possibly because I am hosting on my pc and joining and playing on the same system. However I tested that by moving the server to another local pc and same results at home base where all the major terraforming was done. I tested the theory further by loading my character into a default dedicated server but in a new world nothing done … my vid card amps up, fans speed up, gets to about 60 degrees c … perfect!! And about 140-150 fps !! Then I load back into our dedicated server with all the terraforming, drops the vid card to nothing and 20-30 fps…. Then in our same server I decide to portal to another area in the world where no terraforming has been done but have a couple buildings , lights, fires etc and get between 80-100fps … average around 90. Just on the load start screen of Valheim is crisp and pushes the video card , looks great and 160-170 fps .
This is also with a gsync 240hz monitor. Older i7 processor and 32Gb ram.
So the result is clear, terraforming is a big no no . Our world file size went from 5-6MB to 19-20MB now. Sure I have around 140 hours of game time , only having purchased it 2 weeks or so ago. Lol Amazing game ! Love it , but the low FPS lag at home base is almost enough to sour me and not feel like playing it. The video lag just bothers me. Made me spend countless hours on hardware and software diagnosing before finding the posts everywhere about terraforming and creating unmanageable instances in the game. I could load my backup world file from Dec 25th lol … pre terraforming craziness! But also lose all world progression since then, however thankfully not character progression! But …I now know to NOT Terraform!! I’m hoping the game gets fixed for this sooner than later. However I understand likely not till full release… if and when?

Hopefully this post makes it through as it could be helpful.


6 months ago

Hi James! I’m getting the same CS0104 error that everyone else is getting. I tried spinning up a fresh windows 10.0.19045 virtual machine and running it through that, but it’s the same error even on a fresh windows installation! Any tips?

5 months ago

Thanks for posting this. I ran into the same thing on a Windows 11 computer too and this seems to compile and work fine after for me.

5 months ago

Thanks for the reply James, and sorry for the slightly longer wait. Replacing Debug.Log with UnityEngine.Debug.Log did indeed allow it to compile on the VM! The server booted successfully using the new modded .dll. The VM has never had the server installed on it, and neither has my main machine. The only machine the server was installed on was a remote managed server that I was not able to run DNSpy on. This may be the cause? Regardless, I can’t muster enough people to test the server yet, due to Christmas, but I will let you know the results once we have managed to test it. Thanks for the help!

4 months ago

I tried to do this, I replace all but when I press compile it doesn’t actually change any of them. Any ideas?

2 months ago

That worked for me! Thanks a bunch 🙂

6 months ago

Hi! Thank you for the continued posts and updates. Just attempted a change of send/receive rate for my server and had compile issues after changing the values. Booted up a virtual machine with a fresh install and no luck, same error type and lines of code.

Any way to just edit the text of the file and call it good? I’m pretty sure this is my only bottleneck for my performance and would love to solve it.

Thank you in advance for your help.

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