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MC-168419

Massive frame drops caused by light update while crossing certain chunks

The Bug

Duplicates MC-162253. Why you always find your own ticket duplicate after you create one 😞

Moving from certain chunk to another chunk with certain Render Distance in the certain world will cause massssive FPS lag. I don't know what causes this, but I can provide as much information as I can.

Here's a table with several sets of Render Distance, source chunk, and destination chunk which cause massive FPS drop. I believe the spawn chunk is (1, 5).

Render Distance

Source Chunk

Destination Chunk

2

(0, 0)

(0, 1)

2

(0, 8)

(0, 7)

2

(1, 8)

(1, 7)

2

(2, 8)

(2, 7)

2

(3, 8)

(3, 7)

2

(-3, 8)

(-3, 7)

2

(-2, 8)

(-2, 7)

3

(-4, 3)

(-3, 3)

3

(-4, 4)

(-3, 4)

4

(-5, 1)

(-4, 1)

4

(-5, 2)

(-4, 2)

5

(-6, 0)

(-5, 0)

6

(-6, -3)

(-6, -2)

7

(-7, -4)

(-7, -3)

7

(-6, -4)

(-6, -3)

8

(-9, -4)

(-8, -4)

8

(-8, -5)

(-8, -4)

h3. To Reproduce

  1. Download the attached World File.7z. Extract it to .minecraft/saves/. (The whole world is too large to upload, so I deleted many regions.Β The bug is still reproducible with the attached world file.)

  2. Enter the world.

  3. Set your Render Distance to 2.

  4. Move from chunk (0, 0) to chunk (0, 1).

    • ❌ Notice massive lag.

    • ❌ Notice root.gameRenderer.level.light_updates takes too long in the game log.

  5. Move from chunk (0, 1) back to chunk (0, 0).

    • βœ” Notice little lag.

  6. Set your Render Distance to 4.

  7. Move from chunk (0, 0) to chunk (0, 1) again.

    • βœ” Notice little lag.

  8. Move from chunk (0, 1) back to chunk (0, 0) again.

    • βœ” Notice little lag.

Linked issues

Attachments

Comments

migrated

I checked this out and can confirm that this occurs for me too. I also didn't know there was a log so thanks for that.

The lag spike will occur crossing -9, -4 into -8, -4 all the way up to -9, 11 into -8, 11 when render distance is set to 8. A total of 15 chunks along the Z axis.

SPGoding

(Unassigned)

Confirmed

(Unassigned)

1.15.1

Retrieved