Proxy

Overview

The proxy is special because it is aware of certain parts of the game server's internal state: mainly the chunk locations of each player. This allows to do regional broadcasting very efficiently from the game server. Taking compute and I/O off of the game server allows for a massive performance boost as the game server can only vertically scale while the proxy can horizontally scale.

Operation Type	Vanilla Minecraft	Proxy-Based Approach
Global Broadcast	Server sends one packet to every player	Server sends one BroadcastGlobal packet to the proxy. The proxy will send a packet to each player.
Local/Regional Broadcast	Server sends one packet to each player in a region	Server sends one BroadcastLocal packet to the proxy. The proxy will send a packet to each player in a region.
Unicast	Server sends one packet to a specific player	Server sends one Unicast packet to the proxy. The proxy will send a packet to a specific player.

Using a proxy is a massive optimization for large player counts. For example, to update player positions in Vanilla Minecraft, the server would need to send every player's position to everyone in the same area as that player. In the worst-case scenario where every player is in the same area, meaning that every player needs to know the position of every other player, the server would need to send $n^2$ packets where $n$ is the number of players. This would lead to a large amount of CPU, memory, and network usage from one server. However, with a proxy-based system, the server would only need to send $n$ packets to each proxy. Although there would still be $n^2$ total packets sent from each proxy, this work is spread out across multiple proxies instead of being done on one server.

Ordering

Many of the server-to-proxy packets have a specific order field. The order is calculated as

system_id << 16 | order_id

where system_id is the strictly increasing ID of the system that is sending the packet and order_id is a thread-local counter that is incremented on each packet write.

This allows the proxy to reorder the thread-local buffers from the game server into one buffer that has the same logical ordering as the order of the systems and the order of the packets within each system.