How Consistent Hashing Powers Scalable Memcached Clusters

Caching is one of the most important techniques for improving website performance: it stores data in memory for faster request responses and reduces database pressure by serving many data access requests from the cache.

Today, the most widely used caching services in websites are Memcached and Redis.

Taking Memcached as an example, an application accesses a Memcached server cluster through a Memcached client. The routing algorithm module calculates which server should be accessed based on the key provided by the application, and then the communication module reads or writes data to the selected server.

If a Memcached cluster needs to cache more data or handle higher concurrent access, you simply add new servers to the cluster and update the client’s server list, after which the application can access the newly added servers.

It is important to choose an appropriate routing algorithm. Using a simple modulo hash can cause massive cache misses when a new server is added, effectively bringing the entire cache cluster down. Modern Memcached deployments typically use consistent hashing, which minimizes the impact on existing data access when new servers are added.