Chicken Jockeys causing lag on Multiplayer servers

I was just about to report this also. Good Job reporting it and it explains the problem very well! 🙂

I just wanted to add when these zombies that don't despawn will cause areas of the map to become void of mobs except where the chickens are laying eggs and zombies are picking them up. This causes pockets of 100+ egg holding zombies in a very small area. When you find this Mega mob pockets fighting them although fun is almost completely impossible.

Found the same on SMP. I was getting block lag for the first time and did a force crash wondering if this was happening to me as well. Sure enough, I found a number small pockets (near each of my bases, reached via a nether hub) with dozens of zombies and 5-6 chickens in each. I was clearing them out manually, but it got to the point that I just switched to peaceful and visited all my primary areas to force them to clear. Of course this will be very temporary as there are still chickens in those places and the next time zombies start spawning in them, it will happen all over again.

To try and show the scale of this issue, and to try and help fix it: I've had one of my friends write a bukkit plugin that scans loaded chunks for zombies, checks their inventories for eggs and despawns them. I loaded my servers world in 1.7.2 bukkit and flew around places to try this "fix" and counted hundreds of zombies each time we ran the wipe command. In one area people frequent almost 24/7, there were almost 300 zombies with eggs underground. In a span of 15-20 minutes we killed close to a thousand in different bases, and this has only been in the last week. I am seriously considering reverting back to 1.7.2 and telling my users to stop using minecarts again. 😞

It seems that the chicken jockeys continuously spawn in more chickens, which begin laying eggs everywhere, which causes the zombies to pick them up, which causes pockets of persistent zombies who do not contribute to the mob cap. This generates much more lag than you would think because the server is loading in more hostile mobs than it should be.

I don't know about the lag. I can confirm that I'm seeing chickens running around in the nether, and their eggs are all around as well. I have an overworld mob farm where it "seems" that chicken jockeys are falling from a height of 40+ blocks, they rarely survive the fall, but the chickens do survive. So at my collection base (hoppers/chest) way out above the ocean I have chickens running around and laying eggs.

If this is a complex issue to resolve, I suggest a simpler work around for the time being:

• Don't let zombies pick up eggs

You'll still end up over time with an entity count problem for chickens, but the chicken jockey spawn rate should be much lower than the regular zombie spawn rate.

I'm not sure I would support such a workaround, but it would probably be a quicker hack. Also keep in mind that the zombie AI is much heavier than chickens so even if the number of chickens were high, it wouldn't have quite the same impact on performance as 40-50 zombies. I do however have a concern on how to resolve existing occurrences of this once fixed - my only current thought is to use one of the x-ray glitches in areas I have FPS issues and try to locate pockets of zombies already spawned...

That sort of fix is lazy patching that should not be promoted.

Dropped items have a "Thrower" NBT tag, which exists only when a player drops an item themselves, storing the name of the player that dropped the item. A better fix would be to only apply the "PersistenceRequired" tag to mobs picking up items if the item was dropped by a player. That, or prevent them from picking up items that weren't dropped by the player at all. That information is already stored on the item, so it could be a viable fix.

That sounds better to me, but I do know of a few (very few) users who have created mob cap holds by using something like a cave with a dropper in it to force this issue and prevent spawning elsewhere. Obviously these users developed them before 1.7 caused this...

I'm not sure the inner workings of minecraft. But isn't the most appropriate solution to somehow attach the chicken to the rider, and on whatever event that despawns the rider, despawn the chicken as well?

As a temporary fix (On my servers) we've reverted to 1.7.2 bukkit, and I've had a friend write a plugin to remove any zombies holding eggs every hour.
What once was thousands of zombies-holding-eggs have now lowered to near nothing, and the "leftover" chickens underground catch 2-3 zombies an hour.

I'd love to be able to use vanilla 1.7.4 again! But, any large server is going to (eventually) lag like crazy.

If the chicken can lay eggs while having a zombie ride it, the issue would still remain although rarer.

EDIT: So an additional fix on par with what you suggest would be to change the logic of when the chicken can lay an egg - if something is riding it, it can't lay an egg.

This is a HUGE issue. I started a new world just a few days ago as a tryout server for my main server and have (among other things) been AFKing near spawn to let plants grow and a chicken farm run. Then when I get around to going caving the caves are FULL of chickens. Chicken jockeys may be rare but leave a world running for a while and you get a huge buildup of chickens, which cannot be removed by any means except exploring dark areas to kill them by hand because switching to peaceful doesn't even despawn them. Never underestimate the amount of lag that can be caused by passive mobs, because they simply build up without disappearing. Within a matter of weeks (if not days) every survival world will be brought to its knees by an invasion of thousands of unsolicited chickens. You might as well implement Zelda chicken AI and label them as hostile mobs. 😉

In all seriousness, I suggest making chickens despawn when the riding zombie despawns (although not when it is killed via other means) and making eggs part of a list of items that mobs cannot pick up (including rotten flesh and other common mob drops). That second point should help clear up the issue of passive (not initiated by a player) zombie buildup because as it is zombies can also build up in cases when other mobs die near them. Simply making zombies despawn if the item is not dropped by a player would not be ideal because a zombie could pick up an item that a player mined or shot from a dispenser and despawn with it.

For what it's worth, one of the Mindcrack guys (GenerikB) just did a video today discussing this and cleaning out a bunch of their server's spawn area caves. He mentions that these kinds of fixes are on their way (no clue when the next snapshots will be...), but that the players on the server would need to clean out their base areas manually - just as you note. He uses a resource pack that would normally be cheating (to turn the world transparent), but in the case of this issue it allows you to find the pockets of zombies and chickens much quicker. Of course he isn't one of the Mojang guys so it can't be called official, but those guys seem to know fairly far in advance on some of these things...

The chickens in the Nether have some game balance implications, being "food native to the nether". I suspect that en masse they'll eventually drift down to the lava sea or set themselves afire, but that'll be slow, and the egg thing is a problem. The idea of a hostile nether-chicken has its points...

ETA: But "chicken clubs" in the overworld could be a problem....

SkylinerW: The problem with your fix is that then zombies/pigmen can swipe the drops of their fellows and despawn with them, which is the OTHER half of why picked-up items make mobs persistent. Frankly, I'd be fine with zombies not picking up eggs.

I apologise for asking this question here but how was this issue resolved? I no longer have Twitter to ask a Mojang staff member.

@Martin:

I'll do it for you! I'd like to know, too.
I just tweeted to Dinnerbone asking how he fixed it.

I've done some testing of this and from what I can see it looks to be only partially fixed. Here's my test:
Spam zombie eggs until you get a jockey (I used a dispenser hooked to a clock) into a sealed chamber. Make it with glass so the zombie doesn't take suffocation damage when the chicken is too close to the wall, cover it with opaque blocks to prevent sunburn.
Teleport 128 blocks away and wait about 30 seconds
Teleport back, and I found that the chicken and zombie were both gone (hard to say if they despawned or glitched into oblivion somehow).
Repeat the test, however instead of teleporting away, walk 128 blocks away and walk back. 9 out of 10 times, the zombie was gone but the chicken remained.

Assuming the intention was for both chicken and zombie to despawn, it doesn't always work as intended.

After doing various tests it doesn't seem fixed at all. The chickens don't despawn when the zombies do, the chickens still lay eggs and zombies still pick up eggs.

I'm starting to reach the same conclusion. Also, without getting an answer on "how" the fix was supposed to work, we still don't know if existing chickens and/or zombies will despawn. Do I need to go flush all the random chickens running around the world out or do some kind of kill command (and then rebuild my farms from eggs)?

The fix for 14w02a was broken, it only started working in 14w03a. The fix was put in 1.7.5 as well.

According to Reddit, this has been fixed in 1.7.5 as well.

But only because I claimed so. Don't worry though, I quickly tested one aspect of the fix: I had a chicken jockey spawn, flew away so the zombie would despawn and when I came back, the chicken was gone as well.

...that was actually your post, I just didn't see your comments as the time iI changed the Fixed Versions. Thanks.

Not fixed in 1.7.5
Chicken Jockeys are still lay eggs. And Egg Zombies will not despawn.

Oh, you are right. The bug only is half fixed: chickens now despawn with their riders, but they still lay eggs.

edit: 1.8 snapshot chicken jockeys do not lay eggs, however.

Very good, that is the only reason I updated my server software to 1.7.5. I hated my console being spammed with "Can't keep up!"

This is definitely still causing problems in 1.7.5, possibly because of MC-44778. This morning I found a bunch of chicken jockeys in the collection area of my mob farm (not unexpected). However, the zombies were quickly suffocating in the walls of the collection area and the chickens were left behind and definitely laying eggs. I just upgraded the server yesterday, so I may restore a 1.7.2 backup as I am worried about the potential lag issues.

Still lay eggs in 1.7.6 pre-1

still an issue in 19w46a

This issue can be confirmed on 1.17, can this be reopened?

Issue back in 1.17 Please re open this issue. It has actually gotten so bad on our server it can actually crash. 

Same problem. Hope be solved soon.