Minecraft – How to protect the Iron Farm villagers from lightning

Most of what you're asking can be found on a couple of articles on the minecraft wiki site, but I'll summarize the big points:

• Villages are specified by the existence of doors that meet certain conditions. For a door to be counted as "in a village," the door must have more blocks on the outside than on the inside and a villager must exist nearby - no more than 16 blocks horizontally and 3 to 4 blocks vertically. A block is counted as inside if it is shaded from above. A block is counted as outside if the sun hits it from above. Here are some common techniques for registering doors.

• If the distance requirement for a villager nearby a door is not met, the door can become unregistered after some time. That can be resolved by destroying it and replacing it.

• Each door can support .35 of a villager, i.e. you need about 3 valid doors for each villager (more precisely, every 20 doors support 7 villagers).

• The boundary condition seems a bit hazy, but the 16 block requirement in the first point seems to imply that it's 16 blocks from the most outlying door. However, villagers can move up to 40 blocks beyond that before they actually unregister from their village.

• You must have at least two villagers if you want to start an entirely new village. That means you've either got to find a village and transplant villagers from there, or cure Zombie Villagers using a Splash potion of Weakness, Golden Apples and time.

  • Once you have two villagers, you can have them create new villagers by "making love" (villagers are genderless, so any 2 will do).

  • Villagers will attempt to birth new ones when the village can support more than the current number, as per the third point (doors can support .35 of a villager).

• Iron golems spawn when there are at least 16 adult villagers and at least 21 valid doors.

• Iron golems and villagers both will wander aimlessly if they are not created naturally or are not in a village, respectively.

This information is valid as of snapshot 12w21a, version 1.3.1.

EDIT: To answer the more specific questions OP had...

I don't think anyone really knows, except for the developers, where the hard cutoff for the village is, or if this is one. Apparently at some point, Notch was going to put in some physical boundaries for the villages, but they might not even exist in newer releases.

This mod claims you average out all the locations of the valid doors for the village center, then that the boundary is the largest distance from the center to the farthest house (or 32, if there are no other houses) but it's not clear whether the mod maker thought of these arbitrary boundaries or whether they're actually in the game. I'm going to stick with what the wiki implies and say that villagers register to a village and probably wander up to 16 blocks beyond the outermost doors, and only deregister from the village if they're beyond 40 blocks.

Other than the typical solutions such as installing optifine, you can also dive deeper into the game mechanics and modify those to improve performance.

Vanilla achieves 'random' growth by selecting several thousand blocks each server tick, checking if they can grow or decay, and if they can, applying the growth or decay. This is the 2nd biggest drain on CPU, behind entities.

Seeing as its a farm... there's going to be a lot of calculations going on.

You can of course reduce this number of blocks per tick by installing Spigot and changing the config there, at the cost of slower growth of your crops on your farm.

There are various options you change to be checked at slower intervals, just a few are:

• Snow form
• Ice melt
• Reducing number of mobs that spawn (those in caves under your farm still use up resources)
• Leaf decay

Of course, upgrading your hardware is probably the most effective solution. It is most likely that the CPU will be your bottleneck, but RAM may also be the issue. Use F3 to check the RAM usage in-game.