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  1. Minecraft: Java Edition
  2. MC-129620

Mob spawning algorithm is super slow


    • Icon: Bug Bug
    • Resolution: Fixed
    • Minecraft 1.13-pre2
    • Minecraft 18w20a, Minecraft 18w20b, Minecraft 18w20c, Minecraft 18w21a, Minecraft 18w21b, Minecraft 18w22a, Minecraft 18w22b, Minecraft 18w22c, Minecraft 1.13-pre1
    • None
    • Community Consensus

      The bug

      The mob spawning algorithm is slow and impacts the game's TPS. This is mostly noticeably in a flat world with the gamerule doMobSpawning enabled; the tps heavily decreases. When checking the source with /debug, it showed mobSpawner as source:

      [00] levels - 99.62%/99.62%
      [01] |   New World - 99.82%/99.45%
      [02] |   |   tick - 98.85%/98.30%
      [03] |   |   |   mobSpawner - 91.42%/89.87%
      [03] |   |   |   entities - 6.79%/6.67%

      The lag impacts all worlds, but the amount of impact depends on how many mobs are able to spawn. (normal world with high render distance will lag more than a normal world with low render distance, for example)

      How to reproduce (using a flat world, since it's most noticeably there)

      1. Create a flat world (default settings)
      2. Observe that everything is really slow (slimes, animals, sun)
      3. Disable doMobSpawning:
        /gamerule doMobSpawning false
      1. Now the tps is back to normal

            rherlitz Rikard Herlitz
            AlexMCool Alex³
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