LearnViz CompSci
Home / Learn / Distributed Systems & Cloud / Consistent Hashing

Intermediate Topic 27 of 51 Distributed Systems & Cloud

Consistent Hashing

Key distribution minimizing movement when nodes change.

How it works

Consistent hashing maps both keys and nodes onto a circular hash space, the ring, and assigns each key to the first node clockwise from its position. When a node joins or leaves, only the keys in its adjacent range move, about 1/n of all keys, instead of nearly everything as with modulo hashing. Virtual nodes give each physical server many positions on the ring for even distribution and heterogeneous capacity, and replication places copies on the next several nodes.

Where it is used

Distributed caches such as Memcached clients, key-value stores such as DynamoDB and Cassandra, load balancers and content delivery networks use consistent hashing to spread data and minimize remapping.

Common pitfall

Without virtual nodes, the distribution is uneven and hot spots appear. Hash function quality matters. Popular keys still overload a single node regardless of the hash. Membership changes must be propagated consistently or clients disagree on placement. Rebalancing data transfer takes time. Choose enough virtual nodes and monitor per-node load.

Where it fits in the course

Consistent Hashing is topic 27 of 51 in Distributed Systems & Cloud, rated Intermediate. It follows Saga Pattern. The next topic is Distributed Hash Tables.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Distributed Systems & Cloud quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Consistent Hashing?
Key distribution minimizing movement when nodes change. It belongs to Distributed Systems & Cloud and is an intermediate-level topic.
Where do people use Consistent Hashing?
Distributed caches such as Memcached clients, key-value stores such as DynamoDB and Cassandra, load balancers and content delivery networks use consistent hashing to spread data and minimize remapping.
What is the most common mistake with Consistent Hashing?
Without virtual nodes, the distribution is uneven and hot spots appear.
What should I learn before this topic?
Start with Saga Pattern, the topic just before it in Distributed Systems & Cloud.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Distributed Systems & Cloud quiz. You can also explore Hash Table in the Visual Lab.
Is Consistent Hashing hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Consistent Hashing?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Consistent Hashing?
Saga Pattern, Distributed Hash Tables, Two-Phase Commit are closely connected. The full list is in the related topics section of this page.
What should I study after Consistent Hashing?
Continue with Distributed Hash Tables, the next topic in Distributed Systems & Cloud.

Related topics