consistenthash

Consistent hashing is a special kind of hashing technique used in distributed systems. Its primary goal is to minimize data remapping when the number of servers in a distributed hash table (DHT) or cache changes. Traditional hashing methods, like simple modulo operations, require a complete redistribution of data across all servers when a server is added or removed. This can be very inefficient, especially for large datasets.

Consistent hashing addresses this by mapping both servers and data items onto a ring, typically a circle representing a large range of hash values. When a server is added, it is placed on this ring. Only the data items that fall within the range between the new server and its predecessor on the ring need to be remapped. Similarly, when a server is removed, its data is remapped to the next server in line on the ring. This localized remapping significantly reduces the overhead compared to rebalancing the entire dataset.

The key advantage of consistent hashing is its ability to maintain a relatively stable mapping of keys to servers, even as the server pool fluctuates. This makes it well-suited for distributed caching, load balancing, and distributed databases where dynamic scaling is a common requirement. While it doesn't eliminate remapping entirely, it ensures that only a small fraction of data is affected by such changes, leading to better performance and availability.