How to reduce lag on a Minecraft server

Which kind of lag is it?

Only the first one is about the server. The server runs at 20 ticks per second (TPS). Each tick has 50 milliseconds; when a tick takes longer, the server falls behind and the whole world slows down for everyone.

Measure it with spark

spark is a free profiler that shows exactly what the server spends its time on. It is available as a plugin for Paper and as a mod for Fabric, Forge and NeoForge.

1. Install spark from the Plugins or Mods tab and restart.
2. When the lag happens, type /spark tps. It shows TPS and MSPT, the milliseconds per tick. Under 50 MSPT is healthy.
3. Start a profile with /spark profiler start, let it run for two or three minutes while the lag is there, then /spark profiler stop.
4. spark gives a link to a report. Open it and expand the biggest entries: they tell you whether entities, chunk loading, redstone or a plugin eats the time.

View distance and simulation distance

These two settings in server.properties have the biggest effect of anything you can change, and they do different things.

• view-distance is how far players can see. Chunks in that range are sent to players but not simulated.
• simulation-distance is how far around each player the world is alive: mobs move, crops grow, redstone runs.

Simulation is the expensive part. Lowering simulation-distance to 6 while keeping view-distance at 10 keeps the view the same and takes a large load off the server. Players only notice that farms far away from them stop running, which they do in singleplayer too.

Entities: the usual suspect

In most spark reports on busy survival servers, entities are at the top: mobs, dropped items, minecarts and item frames. Common causes:

• Mob farms that collect hundreds of animals or villagers in one place.
• Item farms without a collection system, so thousands of items lie on the ground.
• Large animal pens. Cows and chickens tick like any mob.

Talk to the owners of big farms first. On Paper, config/paper-world-defaults.yml also has limits, for example on how many entities can push into each other, and bukkit.yml controls how many mobs spawn per player.

Pre-generate the world

Generating new terrain is one of the heaviest things a server does. When players explore in different directions on a fresh world, TPS drops. Generating the area in advance, while nobody plays, removes that cost. Pre-generate your world shows how, straight from the World tab.

Server software and mods

• On vanilla? Switch to Paper in Settings. It is the same game with much better performance, and the world stays as it is.
• On Fabric? Add performance mods such as Lithium and FerriteCore. They change nothing about gameplay.
• Heavy plugins: if spark points at one plugin, look for a lighter alternative or check its settings. Plugins that scan the whole world, like some anti cheat or map plugins, can be heavy.

When it is not the server

If spark shows 20 TPS and players still complain, look at their side. High ping comes from distance and the player's own connection; a player far away from the server always has more delay. Low FPS is solved on the player's computer, for example with the Sodium mod, lower render distance, or closing other programs.