Here’s my assumption-
When 1.7.4 was released they introduced the chicken jockey, the baby zombies that ride on chickens. Before that, chickens were only coded in the game to spawn on the surface, but with 1.7.4, it allowed them to spawn anywhere a zombie could, because the game registers them as a zombie. So, now they’re allowed to spawn underground. Due to the fact that chickens lay eggs, eggs will now be underground as well and seeing as how the caves are an enclosed area, the chickens will not despawn because the game registers them as “trapped” since they are confined. Any time a zombie with the ability to pick up an item walks by, he will snatch up an egg and hold it. Any zombie holding an item will not despawn. Therefore, the damn chickens running around are actually creating a zombie army that will never leave. I went underground in spawn, which is a chunk that stays loaded into the game at all times. I counted and I literally found 111 zombies in about a 50×50 block area. Every single one of them was holding an egg. Now picture that happening under spawn, under Skampp’s place, your place, TimeLord’s, Nuke’s… you get the point. Anywhere we go and hang out for any length of time will create a zombie horde underground that won’t despawn.
GenerikB did a video on the MindCrack server titled “Lag Busters” and demonstrated the same problem. I really do feel like this is the cause of the problem from what I can gather. So, when someone goes afk for 10 hours at an iron farm or something like that, not only are they producing iron, but they’re also creating 100s of mobs underground. This is why it’s so crucial to light up every single cave underground to a block light level of 8 or higher. http://www.youtube.com/watch?v=OteFh8Y0QDY
I’ve researched and Mojang claims that the problem will be resolved in 1.8 (June), by A)making chicken jockeys unable to lay eggs and B) having the chickens from the jockeys despawn after a normal time instead of hanging around.
My suggestion to fix the problem-
Change the server back to a previous snapshot, preferably 1.7.2, before chicken jockeys were introduced. No reset would be necessary or anything. It’s just a simple matter of a few clicks by the admin and everything’s great. Problem evaded.
As for the mobs that already exist… thats a bit harder to deal with. We could all team up together and go caving for a few days, killing off every zombie underground holding eggs. This will take ages. We’ve all spread out so there is probably 1000s of zombies running around at this point.
Another solve, which is not vanilla in the least bit, is for the admin to switch the game mode to peaceful, killing all hostile mobs and then back to Hard… or whatever the difficulty is. That would clear out every single zombie in the game, holding an egg or not, and reduce lag instantly.
If everyone wants to keep the 1.7.4 snapshot (we didn’t get anything that cool in that one… just saying) instead of 1.7.2, another option is that we could use command blocks at spawn to change the gamemode and flip the difficulty back and forth. That way when lag starts getting bad, just go to spawn, push 2 buttons, and leave.
Personally, I think that until the chicken jockeys have been fixed, we should revert back to 1.7.2, flip the difficulty to peaceful one time to kill off all the baddies underground and switch it back to its current difficulty and continue on. Update 1.7.4 didn’t offer anything in the way of new content other than the chicken jockeys so technically we wouldn’t be losing any new content at all. It was a pretty lame update honestly. I think they did a little work to the render distance of chunk updates (no big deal), added a Twitch integration (cool, but no big deal), added some bug fixes (as always) and created these damned demonic fucking chickens!!! I really do believe that this will be the easiest, fastest and most logical fix to the game until 1.8 corrects the issue.
I would urge that this be the course of action. I’m very confident that this will fix our problem. Even if people don’t agree and believe I’m wrong, I’d still like to insist on trying this solution, just to see if it will make a difference. It wouldn’t take but 60 seconds or so and wouldn’t do anything at all to break the game. I’ve dealt with this same issue on another server and no one would listen to my suggestion and instead decided to fiddle with the game code and link command blocks to timers and added bukkit plug-ins and all sorts of nonsense and it didn’t work out for them at all. They ended up screwing the server up and every night cycle the amount of mobs spawned in would cut in half, until about 3 nights passed and no mobs whatsoever spawned into the overworld unless you were by a dungeon spawner. Ask Death_Crusader about it, he’s dealt with it too.
I hope this suggestion will be taken into account and strongly considered. I really do feel like this will solve the problem at least until the next update, without the need of any non-vanilla interference. No bukkits, no plug-ins and no days of work underground lighting up the whole server. In less than one minute, the problem can be corrected.