Lag Guidelines

Villagers are consistently terrible for server performance. Best practices are:

Share trading halls with other players where possible, or keep villagers to a minimum if you're using them solo.
Ensure trading halls are loaded only when in use, and are built 9+ chunks away from your base.
Ensure villagers aren't perpetually scared by zombies, as it a) causes small calculation bursts and b) spawns iron golems that will lag the server even more.
- Breaking line of sight between villagers and zombies will prevent them from being perpetually scared.

For automatic farms in general (private or public), best practices are:

Use community farms instead - there are a variety of effective and efficient farms for most essential items.
Use overflow protection in the farm design, so items don't get bunched up anywhere when overproducing.
Make the farm shut down as soon as its storage is full.
Make sure the farm is only loaded when in use, especially farms with a lot of mob spawns or item drops.

For animal farms, killing chamber, or any other similar situation, best practices are:

Ensure mobs are not crammed in small areas, 1x1 holes or water streams, as mob collisions are terrible for server performance and one of the main sources of lag.
Cull any colliding mobs to as few entities as possible, particularly where mobs are bunched up for a long amounts of time.
- For longer AFK sessions, use wither roses or similar mechanics to kill mobs as efficiently as possible.
- For animal farms, simply breed them when required.
Use vines to reduce collisions if you cannot avoid having multiple mobs in a smaller chamber.