This isn't a mod, but it will help with your issue.
I have used this method on my server, and it helped cut down on A LOT of lag.
Download
MCEdit, a world-editing tool, from their website ( http://www.mcedit.net ).
Inside of MCEdit, chose which world you would like to create the border on.
Make walls around the area you wish to have players kept in, using the invisible Block 36.
This method above will keep everyone within the walls of Block 36, allowing no new chunks to form, so your game runs faster!
Hope this helps!
gaming.stackexchange.com/users/63122/Andrew
Not to my knowledge.
The only mods that are still up to date with Minecraft are Bukkit plugins only.
Also, while it is possible for large worlds to cause memory usage issues, it's not the most common of issues.
I'm sure you've already done your research, but you may want to verify that it is in-fact, a world size issue.
gaming.stackexchange.com/users/50823/Linuxmint
Yes, you can, and you can do it without any mods or external editors, and without generating all of the terrain you want to section off.
You can do this by setting up a simple redstone clock circuit connected to one or more command blocks .
If, for example, you wanted to limit players to within 2500 blocks of 0,0, you could then use the player selector @a[x=0,y=64,z=0,rm=2500] to select all players "out-of-bounds".
Just make sure that this setup is encased in bedrock or inaccessible from non-op players.
Using this, you could do things like tell them to turn around using /tell , teleport them back to spawn using /tp or /kill them outright, or anything else you want such as progressively slowing them down with /effect as they wander off.
gaming.stackexchange.com/users/9350/dlras2
As anyone hasn't said anything about the reasons behind exploring, I thought I could share some experience (although this might be dated).
Maps more often than not concentrate a very large featureless biome (desert or tundra) on the start point.
As Minecraft concentrates certain resources (such as sugar cane, or snow, or even wood) on certain biomes, the key to having a good map would be to get a seed that somehow concentrates any desirable feature around 640 to 1152 blocks of the center point (as all strongholds are located at random positions in that radius).
Then, as suggested by @Tech, you can wall off the exterior sections.
I must tell you that it is impossible to completely cut off a section of a map.
Minecraft was made to be an endless experience.
Walling the "real world" doesn't wall off the Nether.
Assuming you could wall off the Nether, people could, with some effort, climb the walls.
I have sporadically used some mods but they failed more often than they should.
The best course of action, all considered, is to ask gently not to explore much.
And the best way to prevent that is by limiting the urge to explore.
gaming.stackexchange.com/users/54659/Doktoro Reichard
I had a similar issue.
I bought a $10 a month hosting plan from DigitalOcean, and needed it to not use up the 1 gig of memory I had, as I needed to run some other servers.
Simply use world border!
If you have a 1.8 server, you can use /worldborder
set number of blocks to set the maximum number of blocks players can go from the world spawn point.
You can set that too with /setworldspawn.
You can read more about these commands at http://minecraft.gamepedia.com/Commands#worldborder and http://minecraft.gamepedia.com/Commands#setworldspawn
You can also disable the Nether in server.properties if you wish!
gaming.stackexchange.com/users/138538/atoms118
I was hoping to have a pure vanilla server, but the size of the world is causing huge memory usage when only a few players are on the server. Is there a way I can prevent users from exploring so far in the vanilla version of Minecraft?
How can I prevent a world from getting too large without installing plug-ins?
gaming.stackexchange.com
<minecraft-java-edition><minecraft-java-edition-server>
gaming.stackexchange.com/questions/144800
gaming.stackexchange.com/users/63143/crmepham
Try limiting the urge to explore. While it is nearly impossible to limit a Minecraft world, without mods, it seems that the user can take some actions that might work, such as using commands.
Users suggesting few things that might work.