Consistent Hash Ring

Summary

Consistent Hashing Ring is a special hashing algorithm primarily used for data distribution and load balancing in distributed systems. It maps the hash value space onto a ring structure, ranging from 0 to 2^32-1. This approach allows us to better handle node addition and removal while minimizing data migration. Basic Principles of Consistent Hashing Ring The core concept of consistent hashing ring is to visualize the entire hash value space as a circular structure with its ends connected, ranging from 0 to 2^32-1. In this circular space, we first need to distribute server nodes around the ring. Each server node is assigned a position on the ring through a hash function that calculates its hash value. When we need to store or retrieve data, we use the same hash function to calculate the data's hash value to determine its position on the ring. After determining the data's position, we move clockwise along the ring until we encounter the first server node, which becomes the storage location for that data. This mechanism ensures a stable and predictable mapping relationship between data and servers. The elegance of this design lies in its handling of server node changes. When adding or removing server nodes, only the data distribution between adjacent nodes is affected, avoiding global data redistribution. This significantly reduces data migration costs during system scaling or node failures. Why Virtual Nodes? In practical applications, the basic hash ring has a notable issue: when there are few server nodes, data distribution can become highly uneven. This occurs because hash function results may not be uniformly distributed around the ring, causing some server nodes to handle more data while others remain relatively idle. This data skew seriously affects system performance and availability. As shown in the figure below, with only 10 physical nodes and no virtual nodes, we can clearly observe the uneven data distribution. Each ring segment represents a node's data ran...