KeyNotFoundException in new client instance when a certain number of NetworkObjects are present

[lcompton]

Describe the bug
If there are more than 41 non-player network prefab instances, new clients consistently throw a KeyNotFoundException. The client is left in a broken state. It looks like the player prefab is prevented from spawning due to the exception.

I have tried different ways of creating the objects in the server including manually adding them to the scene and spawning via the NetworkManager. The results are strangely consistent (it always fails at 42 or more objects).

Sample project attached.

To Reproduce
This is a Netcode application. The best way to reproduce the problem is to build it (with Development Build selected) and run two instances of it. There's a simple UI. In one instance, click "Start Host", in the other click "Start Client". You should see the error in the client instance.

I don't know if the number of prefab instances is significant, although I have recreated this problem on two computers.

In the "Root" scene, there's an object called "DynamicObjects" that has a component called "ObjectSpawner". You can change the number of objects spawned in the Inspector.

Environment (please complete the following information):

• OS: Windows 10
• Unity Version: 2021.2.7f1
• Netcode Version: 1.0.0-pre.3

Sample Project
SpawnBug.zip

[NoelStephensUnity]

Hello @lcompton,

I looked through your project (thank you for including this, it made it very easy to assist you with this issue) and determined that you were most likely experiencing a limit of the UNet network transport's Message buffer size. It would appear that the default U Net Transport Message Buffer Size of 5120 bytes was too small to be able to update the client with all of the spawned objects (i.e. Host starts and immediately spawns 100 objects, then client joins, Host tries to send the client the information for the 100 objects but the message is truncated and only 42 + a portion of a 43rd is sent to the client). This is why you should get one error about that partial 43rd client:

By increasing the Message Buffer Size to 65535 (maximum size) you will see that all 100 objects are synchronized properly.

Let me know if this addresses you issue?

[PunnetRed]

Hi @NoelStephensUnity ,

I had the same issue as @lcompton, as per the forum thread: https://forum.unity.com/threads/netcode-for-gameobjects-keynotfoundexception-in-client-for-non-player-networkobjects.1217268/

Your suggestion has resolved the issue in my project - thank you very much for your help!

Would you also be able to explain if there are any negative ramifications for maxing out the Message Buffer Size?

[lcompton]

@NoelStephensUnity,

Thanks for the reply. This does solve the problem that I described, although it'll reemerge with a higher number of network managed objects.

Since UNet is deprecated, I'm satisfied with this resolution. I've played around Unity Transport and have run into similar problems to those described in #1570. I'm concerned with scale limitations and will be keeping a close eye for a resolution to that issue.

Thank you for your time.

[NoelStephensUnity]

@lcompton
I have opened a discussion on this issue as it does pertain to something that should be "automatically" handled based on the transport's current buffer size whether it is the default, max, or minimum value. There are a couple of ways this could get fixed, but it depends upon when certain features are rolled out for the snapshot system.
worst case scenario: there could be a fix in the near future where the initial client synchronization handles fragmenting the serialization data for the NetworkObjects
best case scenario: in the near future the snapshot system takes over the initial client synchronization of NetworkObjects and it naturally handles the issue.

We are aware and hope to have a path to fixing this issue in the near future.

Thank you for your patience!

[NoelStephensUnity]

@lcompton
As a side note, I was just made aware of this PR that should at least provide you with the ability, using Unity Transport and not UNet, to bypass the 44KB packet size limitation.
There are on-going discussions on a more final solution.

[lcompton]

@NoelStephensUnity,

Thanks for opening the discussion and for the link to the other PR. I appreciate the help!