Welcome to SolosSMP!

One of the most frequently asked questions we receive is, "why is this server so laggy?" While we strive to maintain high TPS (ticks per second), lag is still a common issue on Minecraft servers, including ours. In this post, I will outline the main factors contributing to lag and explain their causes and trade-offs. It is important to remember that running a server involves balancing various factors, including gameplay features, capacity, and performance. Any optimization-related decision will affect at least one of these factors.

The most significant cause of lag on Minecraft servers is many entities, including dropped items, monsters, animals, and NPCs like villagers. Each entity type has its source of lag, such as path-finding, which can be particularly intensive for villagers and monsters. On SolosSMP, we have disabled zombie aggressiveness toward villagers, as it was using up to 15% of each tick. Entity collisions can also contribute to lag but can be reduced with configuration. We have set per-chunk limits for each mob type in addition to spigot/bukkit's spawning limits to enable players to build efficient mob farms without causing too much lag. However, these limits may result in fewer naturally spawning mobs, which can frustrate players. Paper’s per-player mob spawning is a practical solution but requires balancing farm efficiency and vanilla gameplay.

We have conducted tests that show the extent of the impact of large mob farms on server lag. During one of our temporary maps, with 40 players online, we had 20 TPS, which was a significant improvement. However, pre-regenerating chunks are not always feasible for servers with large world borders, and the server may have to constantly generate new chunks while players are online, which puts more strain on the CPU.

Chunk loading and generation are another cause of lag on Minecraft servers. Paper implements asynchronous loading/saving of chunks, which is a considerable performance boost. However, synchronous chunk loads can be triggered by various events, such as player teleporting or maps, cartographers, or specific EntityPlayer methods when called by the server. This can cause brief but severe lag spikes.

Minecraft Server runs primarily on a single thread, even if the server’s CPU has multiple threads. Minecraft is not optimized to take advantage of more CPU threads, which is a significant challenge for Mojang. On SolosSMP, we use a powerful CPU with single-threaded performance to handle the server. Minigame servers like Hypixel use proxies like bungeecord and load balancers to distribute their players among many back-end servers.

The server's CPU and single-threaded performance limits the number of players playing on a Minecraft server. Shared hosts often use Intel Xeon CPUs not optimized for single-threaded applications. Over-allocation of servers on each node should be avoided. On SolosSMP, we use high-grade hardware within our budget, but the Minecraft server's constraints still limit us.

Garbage collection, the process of deleting unused objects in memory to free up space, can cause lag spikes on servers. G1GC is the default garbage collector in Java, but it can be misconfigured, resulting in lag spikes. Appropriate memory allocation and heap size are necessary.

There are many reasons why Minecraft servers may lag. This post outlined the leading causes of lag on SolosSMP, but they are likely applicable to other survival servers. Our server's optimization is ongoing and constantly tweaking to meet our server's needs. With Mojang releasing new future updates every few months for its game, the optimization needed will continue for the entire server lifetime and will likely never be completed.