[Bug] Copycat blocks on trains causing lag

[dti131]

Too many copycat blocks (of any type) on trains will cause FPS lag for some people, including game crashes. This isn't a system issue: most of the people I know who experience this have at least decent PCs/laptops that are otherwise capable of running Minecraft at 90+ FPS with high render distances, Distant Horizons, Create machines, etc

Steps to reproduce the behavior:

1. Build a large train using at least a couple hundred copycat blocks of any type (panels, bytes, slopes, whatever)
2. Assemble the train
3. Drive train around
4. Decent likelihood that you, or another user on the same server for multiplayer, will experience drops to below 10 FPS or instant game crashes.

Expected behavior
The same framerate as a user would get from looking at any other assembled train, with no crashes or other issues.

Desktop (please complete the following information):

• Minecraft Version: 1.20.1
• Mod Loader: Fabric
• Mod Version: 2.1.4

Additional context
This problem ONLY happens with trains made from hundreds of copycat items. It doesn't happen with trains made with a small amount of copycats or static blocks.
The framerate issues persist, even after leaving the area containing a train built from copycats. The only solution for this is a game restart.

[embeddedt]

Can you run a Spark profile on the client thread with /sparkc profiler start when the lag is happening?

[dti131]

If the trains that were causing the issues are still assembled by the time I get home I can try that. They might have been disassembled and destroyed though, since the issue was affecting all but two players.

…

On Thu, Jan 16, 2025 at 9:01 AM embeddedt ***@***.***> wrote: Can you run a Spark profile on the client thread with /sparkc profiler start when the lag is happening? — Reply to this email directly, view it on GitHub <#187 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AMQBLY5NBGUATQ662VUFTFL2K7QVLAVCNFSM6AAAAABVJ4GVESVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDKOJWGI2DQOJZGQ> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[hlysine]

We do have a few performance fixes in the next update which may help, but without a Spark profile we can't locate the cause.

[carbonatek]

Heyo,
I have fortunately found this issue as I'm experiencing a similar/same issue as the one here, mostly consisting of lag on my work laptop and stutters on my 5700X3D equipped desktop computer when my large (8 carriage) passenger train passes by. Unlike OP, I have recorded a spark profile.
There's only about 300 blocks from Copycats+ on the entire 190m long train.
Online:
https://spark.lucko.me/BFhchEPz8n
Offline (GitHub does not support *.sparkprofile schema):
BFhchEPz8n.sparkprofile.zip

Hope it helps!

EDIT: It's on Forge 43.3.x on 1.20.1 - that is probably the only difference. Oh, and it's Copycats+ 2.2.0.