Low TPS on 1.20.1 Forge server (~100 mods, 3 players). SOLVED: Valkyrien Skies memory leak
Hello, I am running a private Forge server for myself and my friends, but the server isn't performing well.
While not visible in this Spark report, I have tried closing out of every other program to free up 10GB of RAM headroom, and also allocated an additional 2GB (6 -> 8GB) of RAM to the server, but I don't think RAM is the issue. Even with plenty of headroom, the high MSPT persists even though GC is quick and sufficiently infrequent.
Additionally, TPS remains low regardless of if all players are in the same location, loading the same chunks, or if they are spread far apart and loading different chunks. So it doesn't seem to be view- or simulation-distance related (both are set to 10 chunks)
I am certain there are no "lag machines". This is just a normal modded survival among friends.
- Starlight
- C2ME
- Mobtimizations
- Chunky (Used to pre-generate world. There is no chunk generation happening during this spark profile)
Appreciate any help! A second pair of eyes on this report would be wonderful.
Symptoms:
After freshly restarting the server, the TPS sits at a healthy 20.0. But over the course of about an hour, TPS gradually drops down to 10 or even 5 TPS. From the Spark report, there doesn't seem to be any obvious offending mod causing the majority of the lag, nor are there that many entities loaded to result in such low TPS. My hardware should be quite capable of hosting just 3 players (i7-12700K, Samsung 990 Pro M.2 nvme ssd, DDR5 5600MHz memory)While not visible in this Spark report, I have tried closing out of every other program to free up 10GB of RAM headroom, and also allocated an additional 2GB (6 -> 8GB) of RAM to the server, but I don't think RAM is the issue. Even with plenty of headroom, the high MSPT persists even though GC is quick and sufficiently infrequent.
Additionally, TPS remains low regardless of if all players are in the same location, loading the same chunks, or if they are spread far apart and loading different chunks. So it doesn't seem to be view- or simulation-distance related (both are set to 10 chunks)
I am certain there are no "lag machines". This is just a normal modded survival among friends.
Installed Performance Mods:
- FerriteCore- Starlight
- C2ME
- Mobtimizations
- Chunky (Used to pre-generate world. There is no chunk generation happening during this spark profile)
Spark Report:
https://spark.lucko.me/JSj5zA06fkAppreciate any help! A second pair of eyes on this report would be wonderful.
Solution
Thanks for the response! These are good insights. However, I believe I found the true culprit after disabling mods one by one. Seems that Valkyrien Skies: Clockwork has a memory leak. Would explain why TPS starts at 20.0 after restart and slowly dips over the course of an hour. After removing Valkyrien Skies and Clockwork, server is maintaining 20.0 TPS for hours on end without changing anything else 
