Consistent Hashing with Virtual Nodes
Solve the N-node reshuffling problem: The 360° Hash Ring, O(K/N) key relocation on node failure/scaling, and Virtual Nodes (Vnodes) for uniform load balance.
01.1. The Fatal Flaw of Standard Modulo Hashing
In traditional hash partitioning across N cache or database servers, keys are mapped using simple modulo arithmetic:
Server Index = Hash(Key) \pmod N
The Catastrophic Failure Mode:
If you have 4 cache servers (N = 4) and you add 1 new server to scale capacity (N = 5), the modulo divisor changes from 4 to 5 for every single key in the universe.
- Over 80% of all keys (
1 - 1/N) are remapped to completely different servers instantly! - In a caching cluster, this triggers a Massive Cache Stampede: millions of cache misses occur simultaneously, hammering backend databases and causing complete cascading failure.
Consistent Hashing Ring with Virtual Nodes (Vnodes) 💍
Consistent Hashing Ring with Virtual Nodes (Vnodes) 💍
Keys and server virtual nodes are hashed onto a circular 360° ring. Keys map clockwise to the nearest virtual node, ensuring uniform load distribution and minimal key relocation during scaling.
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