Minecraft Optifine Lagometer - meaning of white bar?

I am currently trying to figure out why Minecraft is running extremely slow on a specific computer. So I enabled the lagometer an it shows me a huge white bar. Unfortunately, the meaning of white is not explained in the lagometer tooltip. Can anyone tell me what it means? I am running Minecraft 1.12.2 on Windows 10 with Optifine.

Solution 1:

The white top of the line shows the time in the world update part of the code. This is where world blocks and entities get updated, for example: mobs spawning, water flowing, redstone working, trees and plants growing etc. The world update is also known as tick and is performed every 50 ms (20 times per second) independent from the screen update rate. This is why on higher FPS not every lag line has a white top, the tick skips some frames to keep the rate of 20 updates per second.

It means that you aren't rendering everything on screen fast enough. Try turning down render distance.

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