SmoothServer

Actively maintained for Valheim 1.0. Rebuilt for 1.0.7 on launch day and kept current as patches land; version 1.x of the mod is in the works. Bugs and ideas: GitHub issues.

Designed and thought up by Nosferatu from real pain points hit running a co-op server. Coded using Claude, tested by humans.

Networking and performance tuning for Valheim dedicated servers — and, since 0.3.0, an optional client half in the same DLL.

The server half is the point of the mod and it still needs zero client installs: [General] EnforceClientMod defaults to false, so vanilla players can always join. Install the same package on players' machines as well and you additionally get packet compression, a client send budget and a server-wide shared map.

Installing

Server admins — install into the server's profile (BepInEx/plugins/SmoothServer/). Everything under "Server modules" below starts working immediately; nobody has to install anything. Config file: Nosferatu.SmoothServer.cfg in the server's BepInEx/config/.

Players — install into your own profile only if the server also runs SmoothServer 0.3.0+. [General] Mode is Auto: a dedicated server runs the server half, your game runs the client half. You get compression, the client send budget and the shared map; server-owned settings are pushed to you by the server.

The package contains six DLLs, not one: SmoothServer.dll plus ZstdSharp.dll, System.Memory.dll, System.Buffers.dll, System.Numerics.Vectors.dll and System.Runtime.CompilerServices.Unsafe.dll (the zstd codec and its dependencies — none ship with Valheim or BepInEx). A mod manager handles this; hand-installers must copy all six.

Mods this replaces — uninstall them first

Uninstall	Replaced by	Where
CW_Jesse / BetterNetworking	Compression + SteamRates + SendQueueGuard	server and clients
Mydayyy / ServerSideMap	SharedMap	server and clients

Both must go from every machine. If BetterNetworking is still installed, Compression refuses to patch (FAILED(...) in the module summary) and the rest of SmoothServer loads normally — it will not break your server, it just will not compress. SharedMap imports an existing <world>.mod.serversidemap.explored file once on first start, so no exploration is lost.

Server modules

Each module has its own Enabled toggle in its config section.

• Telemetry [Telemetry] — periodic fps / frame-time / ZDO-rate log line. No gameplay effect.
• FrameRate [FrameRate] — raises the dedicated server's Unity frame cap. 60 is a good default on modern hardware: roughly +4pp of one CPU core for half the tick latency.
• SendCadence [SendCadence] — sends ZDO updates to every peer on a fixed interval (SendHz, default 20) instead of vanilla's one-peer-per-frame round robin. Scales with player count.
• SendBudget [SendBudget] — the ZDO send-queue high-water mark and minimum chunk size, exposed as config: HighWaterBytes defaults to 65536 (vanilla 10240), MinChunkBytes to 2048 (same as vanilla). Acts as the fallback when AdaptiveBudget is off.
• CreateBudget [CreateBudget] — objects created per frame, exposed as config (default matches vanilla, i.e. a no-op until raised).
• PeerTelemetry [PeerTelemetry] — per-peer ping, throughput and Steam send-queue sampling. No patches; feeds AdaptiveBudget.
• AdaptiveBudget [AdaptiveBudget] — a per-peer send budget from each peer's measured bandwidth-delay product, clamped, EMA-smoothed, and backed off while Steam's pending byte count says the pipe is congested. A player on fibre next door and one on satellite no longer share one number.
• SteamRates [SteamRates] — raises Steam's SendRateMax (default 1 MB/s). SendRateMin stays at vanilla on purpose: it is a floor on Steam's own bandwidth estimate, and raising it stops the congestion controller backing off for weak connections.
• SendQueueGuard [SendQueueGuard] — defers, never drops, while a peer's Steam send queue is backed up, and survives the Steamworks throws that can occur mid-handshake.
• SyncListCache [SyncListCache] — caches the per-peer sector scan in ZDOMan.CreateSyncList briefly; the filter and sort still run on every send.
• VPOServer [VPOServer] — the server-safe parts of ValheimPerformanceOptimizations (MIT): WearNTear support caching and a faster ReleaseNearbyZDOS scan.
• AsyncSave [AsyncSave] — pre-sizes the save clone list. Measured on a 136 000-ZDO world, main-thread autosave stall 67 ms → 47 ms and 78 ms → 45 ms.
• GcThrottle [GcThrottle] — rate-limits Resources.UnloadUnusedAssets on an idle server.
• OwnershipRelease [OwnershipRelease] — shortens the ZDO ownership-release interval from vanilla's 2 s (default 0.5 s) so objects change hands faster as players move.
• MapSelfTest [MapSelfTest] — headless unit tests for the shared-map codec at load; shows up as applied PASS in the module summary.
• PriorityLane [PriorityLane] — both ends. Holds this machine's outgoing backlog in a priority queue instead of letting it pile up inside Steam's own buffer, and hands Steam only about one bandwidth-delay product at a time, latency-critical traffic first. A melee hit no longer waits behind tens of kilobytes of bulk world data: the residual delay drops from the 80–430 ms band to roughly 25 ms. Unmodded clients benefit too — only the send order changes, every byte stays vanilla. Coexists with SendQueueGuard and Compression; the ordering rules that keep it safe (never let a destroy overtake the object it destroys, never promote a message whose target the receiver has not been sent, never cross Compression's handshake) are unit-tested at load.
• StatsLog [StatsLog] — writes stats-YYYY-MM-DD.jsonl (fps/frame time, ZDO counts, per-peer network/budget/compression state) every IntervalSec (default 10s) and events-YYYY-MM-DD.jsonl (joins/leaves, save stalls, GC sweeps, AdaptiveBudget backoff transitions, SendQueueGuard drops, config reloads) as they happen, to BepInEx/config/smoothserver/stats/ by default. Rotates daily, prunes past RetentionDays (default 30). Run tools/analyze.py against a few days of these files for a markdown report — see the repo's tools/README.md.

What the client half adds

• Compression [Compression] — both ends. zstd over Steam sockets using BetterNetworking's trained dictionaries, with an explicit per-message frame tag and an SS_Caps/SS_Ready capability handshake, so the receiver always knows whether a message is compressed. Peers without the mod stay uncompressed with no penalty. Typical self-test ratio on real ZDO traffic: ~8 % of the original size.
• SharedMap [Map] — both ends. The whole server shares map exploration and pins. The store is bit-packed and compressed (1.7 KB where ServerSideMap wrote 4.2 MB for the same world), the map size is read from your client rather than hardcoded, and updates are batched at 1 Hz into sparse chunks instead of one RPC per explored pixel. Merging goes through vanilla Minimap.Explore, so shared terrain bakes into your own map file and nothing is lost if the module is turned off. Pin sharing is configurable per pin type; death pins are off by default.
• ClientNet [Client] — client only. Your client's own ZDO send high-water mark (default 48 KB, vanilla 10 KB) and Steam SendRateMax. Inactive on a dedicated server.
• CombatOwnership [CombatOwnership] — client only. On a dedicated server the ore, tree or vine you are swinging at is simulated on another player's PC, so every hit is a round trip to them and back — about half a second in a busy cave. This takes ownership of the object the moment you hit it, after which your damage lands on your own machine in the same frame and the hit message never goes on the wire at all. Ore, trees, vines, destructibles and building pieces; bows and AoE included. Creatures are deliberately left alone. Wards, other players' builds, ships and carts are all respected.
• LagProbe [LagProbe] — both ends, diagnostics only; it changes nothing about the game. The server pings each player every 5 s over a routed RPC and reports that player's real RTT, jitter, packet loss and frame rate (all measured on the server's own clock, so it works whatever Steam reports). On your client it times hit registration — from the moment you hit something someone else owns until the owner's answer comes back — and keeps a p50/p95/max histogram plus a per-owner breakdown, and it counts how often objects near you change owner. Type ss.lag in the console for the current summary on either side.

Config

One file, Nosferatu.SmoothServer.cfg. Edits are picked up live on a running server ([General] HotReload) — no restart. Settings the server owns are pushed to clients that run the mod (ServerSync); [General] entries stay machine-local.

Dependencies

• BepInExPack_Valheim 5.4.2350

Credits

• zstd dictionaries and the compression idea: CW_Jesse's BetterNetworking (MIT).
• VPOServer: ValheimPerformanceOptimizations (ontrigger, MIT).
• Config sync: blaxxun-boop's ServerSync (MIT-0).
• SharedMap is a clean-room reimplementation inspired by Mydayyy's ServerSideMap (MIT/Unlicense).
• Server-authoritative ownership idea: ddormer's Serverside Simulations (no published license — idea only, no code taken).

Source & issues

https://github.com/MJensen01/SmoothServer — MIT licensed.