Revision Notes/System Design Concepts
Field Entry - System Design Concepts
Consistent Hashing
A technique for distributing data across servers so that adding or removing a server minimizes the number of keys that need to be remapped.
Field Note - Real-world Analogy
“Imagine a circular clock face. Servers are placed at various positions on the clock (12, 4, 8 o'clock). Requests are hashed to positions on the clock. Each request goes to the nearest server clockwise. If you add a server at 2 o'clock, only requests between 12 and 2 need to be rerouted to the new server. Everything else is undisturbed.”
Field Observations - Key Topics Covered
The problem with simple modulo hashing: you have N servers and route requests by key % N. Works great until you add or remove a server. Now N changes and almost every key maps to a different server. This causes a massive cache invalidation — all cached data is suddenly in the wrong place.
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