Redstone is only expensive when it is running. The trouble is that a lot of common designs run permanently, twenty times a second, in a chunk somebody keeps loaded — and unlike a mob farm, there is nothing to see.
Cost by design
| Design | Cost |
|---|---|
| A door, a lamp, a lever | Nothing. It updates when you use it. |
| An observer watching a crop | Very low. Observers only fire on change. |
| A repeater or comparator clock | High. It updates continuously, forever. |
| A hopper clock | High, and it also pays the hopper cost. |
| A piston loop or flying machine left running | Very high. Block updates are the most expensive kind. |
| Redstone dust in long lines | Moderate. Each dust update propagates to its neighbours. |
Why clocks are the problem
A clock exists to do something repeatedly, so by definition it never stops. In a loaded chunk, a fast clock generates block updates every couple of ticks indefinitely, and each update touches its neighbours.
One clock is nothing. Twenty players each with a clock in their base, all in loaded chunks, is a measurable share of your tick — and no single one of them looks like a problem.
Finding them
- Profile and look for block-entity or redstone time
Spark separates this out. Redstone high in the tree points at a specific chunk.
- Check the spawn chunks first
The always-loaded area is where clocks do the most damage, because they run even when the server is empty.
- Ask before removing
A clock is usually part of something the player built deliberately. Offering an observer-based alternative keeps the machine and the player.
An observer fires only when the block it watches changes. Replacing a repeater clock that polls with an observer that reacts usually keeps the same behaviour and drops the idle cost to zero.
A piston-based loop generates block updates and moves entities every cycle. One abandoned in a loaded chunk can run for months. If your baseline load rose one day and never came back down, this is a candidate.