Slabs in the nether (and other places)

Today I found out that covering areas with slabs to prevent mob spawning causes lag. On a large scale, it can cause so much lag that it uses 50% of the CPU of the whole server. So if you use slabs on a few places to prevent mob spawning, it’s fine. Once you count the places where you use it in the hundreds, or if you cover whole chunks with slabs, you are creating an issue.

The problem comes from the fact that the mobs spawn and de-spawn again on the slabs, as opposed to properly lit areas, where the spawning is prevented before it happens. When the mobs de-spawn, the server has a lineup of mobs to populate the chunk, and it starts from scratch.

So please do not use the slabs as a broad method to prevent mob spawning.

20 thoughts on “Slabs in the nether (and other places)

  1. Question, what about glass and other transparent blocks like glowstone and ice? Do those spawn-despawn mobs like slabs and cause lag?

    • Good question, I have no idea. I would assume they do. If you leave places where the mobs can spawn, it should be OK, but if there is no space, then you create an issue.

    • Slabs are bad in large numbers, Pretty self explanatory.

  2. If I understand well placing glowstone/lanterns to light up the areas is enough to solve the problem, there’s no need to dismount the slabs (I have an ocean monument covered with slabs on the surface).

    • BTW I also assume that water would be another legit way to avoid spawning on a wide scale (in non nether biomes)?

  3. I have most of an empire lot covered in layers of slabs (not to stop mobs from spawning, but because it uses less materials) they are all lit up with torches, so mobs should not try to spawn on them anyway. What do I need to do?

    • If they are lit up with torches.. maybe they are placed in the upper half of the bloc? In that case, they should be no problem, slabs only prevent spawning – apparently despawning right after spawning – if they are placed on the lower half of the bloc, in which case you can’t place a torch on them.

  4. For information, I have placed a few lanterns in the slabs next to the portal at DL’s spawn.

    If anyone want to make that look nice (I just put them randomly) please feel free to do so, I won’t take offense.

  5. This is a big thing in the aether, most plots are covered at the walkway level. There is a lot to be done.

    Will there be a punishment for players that don’t fix their lots? A time frame to do so?

  6. It means glass or stationary water (source blocks of water) should be used in Darklands to prevent mobs spawning. I was using slabs, since it’s the simplest way to have areas safe. It’s just unrealistic to have huge battles every time I need to resume mining.

    So, HUGE amounts of sands will now become very requested.Looks like I know now where to put the sand I am collecting off my desert lots…

    Glowstone is just too tedious to mine. No transparent block can be generated in arbitrary amounts, correct?

    • Stairs also prevent spawning. I suppose some study should be performed whether there aer blocks preventing mob spawning without actual despawning them right away (perhaps water can do that; if it’s stationary, it shouldn’t affect server’ s load that much.)

      • Stairs will create the same lag since the method is the same as the slabs.

        Please consider the following: If you have a wide open area, covering thousands of blocks with whatever is not the way to go. You rather dig a tunnel and you will be able to put slabs there. If you just put one row of slabs per chunk that you move along on, you do not have an issue. Rather think about what kind of structure you can build to move safely along on than converting the nether into a 100% safe area with huge efforts.

        • While we’re at it, I’d like to clarify one assumption that I always make: is it right to think that no calculation at all is done by the server for a zone in which no player is remotely near? (“near” being in the order of 128 blocks in my head).

          • Correct. Areas are loaded when a player is near. Until then, they do not affect the server. I do not know the exact distance though. I assume that there is a mixed effect of general vicinity and if the place is within a certain visible distance.

            • I was curious how far the server loaded chunks from where I play so I planted saplings every 5 blocks to a tremendous distance. I found that they will grow up to 180 blocks away.

              • That’s why I don’t want people to have stuff that causes lag on their lot. The neighbor will trigger it.

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