Reduce lag on a small Minecraft server

A Minecraft server tries to update the world 20 times a second. Each update is a tick. When there's too much to do in one tick, the server falls behind and the game slows down for everyone. Paper's tps command shows ticks per second over the last 1, 5 and 15 minutes. 20 is perfect; below about 18 people start to notice.

The biggest setting is how much of the world stays loaded around each player. In server.properties:

• simulation-distance decides how far away crops grow, mobs move and redstone runs. Dropping it from 10 to 6 cuts the work a lot, and most players never notice.
• view-distance decides how far players can see. It costs less than simulation distance but still adds up with several players. 8 is a good balance.

Restart the server after changing either.

Making new chunks is the heaviest thing a server does. When people fly with elytra or explore in different directions at once, the server generates terrain as fast as it can and everything else waits.

The Chunky plugin generates an area in advance while nobody needs the server. Install it, then run:

chunky radius 2000
chunky start

Keep the server open while it runs; it naps after 5 minutes with nobody online, and Chunky continues where it left off next time. Watch your storage: a radius of 2,000 blocks takes a few hundred megabytes.

Every mob, dropped item, minecart and armor stand is an entity, and every entity costs something each tick. The usual culprits:

• Animal pens that grew to hundreds of cows. Cook some.
• Mob farms that store mobs instead of killing them.
• Item sorters and hoppers by the dozen. Each hopper checks for items every tick.
• Villager trading halls. Villagers are among the most expensive mobs.

Paper already limits many of these, but a few big farms can still bring a small server down.

Guessing wastes time. The spark plugin measures what the server spends its time on. Install it, and when it's lagging run:

spark profiler start
spark profiler stop

The report shows which parts of the game, which plugins and often which chunks take the most time. If one plugin is at the top, update or remove it. If it's entities, the report lists where they are.

Kiphost servers have 3 GB of memory. That's plenty for a group of friends on a vanilla-style world with a handful of plugins. It gets tight with lots of plugins, very high view distance, or many players spread out across the map. If the console shows OutOfMemoryError, remove plugins you don't use and lower the distances.