The bug
When using flint and steel for deforestation, the game performance worsens until is unplayable.
How to reproduce
Go to a forest, light it on fire, wait for the fire to spread.
Examples
[media][media]
Linked issues
is duplicated by
Attachments
Comments


I can confirm this for 1.14-pre1, and 1.13.2 as well - 1.12.2 performs much smoother when there is a large fire. Added two screenshots, one on 1.14-pre1 on a Buffet Dark Forest set on fire, the other one 1.12.2 with a customised Dark Forest only world set on fire, With the F3-Shift screen turned on, going down to the thing that seems to cause the most lag (root.gameRenderer.level.terrain_setup.rebuildNear).
Edit: I do realise that my 1.14 is running on Java 12 (running quite well actually) - I also tested it on the bundled Java with the same result.

Still in all 1.14 Pre-Releases

Still in 1.14 Release

It was easier to have a tree lit on fire and have the game run smoothly pre-1.14. Now it lags too much.

Still in 1.14.1 Release

Still in 1.14.2 Pre-Release 1 and 1.14.2 Pre-Release 2

Still in 1.14.3 Pre-Release 2.

Still in 19w45a and 19w45b.
[media]
What is your biome blend setting?

@slicedlime The biome blend is at its default setting (5x5).

Thanks. Could you post another screenshot like the previous one - with the performance graph, on 19w46a or later please?

@slicedlime Here there are!
[media][media]

@slicedlime Just wanted to add some screenshots on a different system setup.
Biome blend= 3x3 on both versions.
Just to clarify, these are not very trustworthy because at some point being a block or two nearer the fire provokes a HUGE performance drop. I can elaborate more on this if needed.
[media][media]

Affects 20w12a

Affects 1.16 pre release 2

Can confirm for 1.16 pre release 5

still happens in 20w27a

Reporter changed to @unknown upon request in Discord, since the original reporter has been inactive.

Why did you light this poor forest on fire in the first place?

It might not be caused by purposely lighting it on fire, it could also be caused by a lava lake.

Can confirm in 1.17.1. Doesn't even need to be a large forest; a few burning trees are enough to cause frame rate issues.

That's worse in 21w39a

Can confirm in 21w40a.

This issue was fixed, but keeps being reopened. The amount of lag has been reduced by a drastic amount to when this was first introduced. This one must stay closed.

I have created a new ticket for the post-19w45a issue: MC-240450.
I'm afraid this is not a bug, this is lag due to a lot of fire needing to be processed on your PC, just like igniting a ton of TNT at the same time.