- 07-06-2026, 17-55-25.png (4.71 MiB) Viewed 175 times
I am observing a strange performance issue and I am not sure what is causing it.
I started a local dedicated server with mods and connected to it from the same machine via localhost. When playing through the local server, the game has a very significant FPS drop. However, if I open the same save directly in single-player on the same PC, the game runs at stable 60 FPS / 60 UPS.
I understand that in this setup there are effectively two simulations running on the same machine: the dedicated server simulation and the game client. However, the performance drop seems much larger than expected, especially considering the hardware.
PC specifications:
- CPU: AMD Ryzen 9 9950X3D 16-Core Processor
- RAM: 96 GB DDR5, 6000 MT/s
- GPU: 5080 16 GB VRAM
The save is heavily modded. I am using the Py / Pyanodons modpack. I know that this modpack is very large and demanding, but the difference between single-player and localhost dedicated-server gameplay seems unusual.
What I observe:
- Same machine
- Same save
- Same mods
- Single-player: stable 60 FPS / 60 UPS
- Local dedicated server + client connected via localhost: severe FPS drop
What I expected:
- Some additional CPU load because both server and client are running
- But not such a strong FPS degradation when both are on the same high-end PC
What I need help with:
- Understanding whether this is expected behavior
- Finding out if the bottleneck is CPU scheduling, client-server synchronization, networking/transport layer overhead, mod scripting, or something else
- Identifying what diagnostics I should collect to make the issue easier to investigate
Additional context:
Factorio is my favorite game.
I really enjoy building megabases and large-scale factories. I usually play with a friend, and we prefer very large modded playthroughs, especially with complex modpacks like Py/Pyanodons. Because of that, multiplayer performance and scalability are very important for this kind of gameplay.
I know that the next update will be the last of the major ones, and I would really like to see additional optimization time (both UPS and client-server). We've been playing our huge card for literally years.
It would be great if the developers could give more attention to performance in large modded multiplayer saves, especially around the transport/network layer, synchronization overhead, and general optimization for large-scale factories. Factorio is already very well optimized, but large modded megabases can still hit performance limits very quickly.
Please let me know what additional information would be useful. I can provide logs, the save file, the mod list, profiler screenshots, or any other diagnostics needed.
Additional note about multiplayer, trains, and large-scale transport performance:
We also play multiplayer over the network. In this case I usually start the server directly from inside the game client, and the overall performance is also not always ideal. It is playable, but there are already some noticeable delays, small stutters, and synchronization-related issues for the other player.
A particularly important area for us is the train and rail system. Our current base already has more than 3,000 train stations, and this is still not really a megabase by Py/Pyanodons standards. We are only progressing toward the second Pyanodons science pack, so the factory is still at a relatively early stage of the full modpack progression. Even at this point, we can already notice some light performance degradation.
I understand that this is probably not one single isolated bug, but rather a complex performance and scalability issue involving many systems: train pathfinding, rail scheduling, station logic, circuit-controlled logistics, mod scripts, multiplayer synchronization, and general update cost.
It would be very valuable to see further optimization work around large rail networks and train-heavy bases, especially for multiplayer. In large modded factories, trains become one of the core systems, and the number of stations, paths, interrupts, schedules, and logistic dependencies grows very quickly.
For the multiplayer side, I do not necessarily mean a full technical desync. It is more about the gameplay feeling slightly out of sync for the connected player: small delays, uneven responsiveness, occasional stutters, and visible performance drops when the factory becomes more complex. Ideally, even if some latency is unavoidable, it would be better if the experience could remain smoother and more predictable.
I fully understand that Py/Pyanodons is an extremely demanding modpack and that this may not be a simple issue to solve. Still, from the perspective of players who enjoy very large-scale factories and long multiplayer playthroughs, further optimization of trains, rail pathfinding, station handling, and multiplayer synchronization would be extremely useful.
