Hash slots distribution in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a hash slot in Redis Cluster?

A hash slot is one of 16,384 buckets used by Redis Cluster to distribute keys evenly across multiple nodes. Each key is assigned to a hash slot based on its hash value.

beginner

How many hash slots does a Redis Cluster have by default?

A Redis Cluster has 16,384 hash slots by default. This fixed number helps evenly distribute keys across the cluster nodes.

intermediate

How does Redis determine which hash slot a key belongs to?

Redis calculates a CRC16 checksum of the key and then takes the remainder when divided by 16,384. This remainder is the hash slot number for the key.

intermediate

Why is hash slot distribution important in Redis Cluster?

Hash slot distribution ensures data is spread evenly across nodes, balancing load and enabling efficient scaling and failover in the cluster.

advanced

What happens if a node in Redis Cluster fails regarding hash slots?

If a node fails, Redis Cluster reassigns the hash slots owned by that node to other nodes to keep the cluster operational and data accessible.

How many hash slots are there in a Redis Cluster?

A 1,024

B 16,384

C 65,536

D 512

Redis Cluster uses exactly 16,384 hash slots to distribute keys.

What method does Redis use to assign a key to a hash slot?

A Random assignment

B MD5 hash mod 1,024

C SHA-1 hash mod 65,536

D CRC16 checksum mod 16,384

Redis calculates the CRC16 checksum of the key and then uses modulo 16,384 to find the hash slot.

Why does Redis Cluster use hash slots?

A To evenly distribute keys across nodes

B To encrypt data

C To compress keys

D To store keys in a single node

Hash slots help spread keys evenly across cluster nodes for load balancing.

What happens to hash slots if a Redis node fails?

A They are deleted permanently

B They remain unavailable

C They are reassigned to other nodes

D They are backed up automatically

Redis Cluster reassigns hash slots from the failed node to keep data accessible.

Which of these is NOT true about Redis hash slots?

A Hash slots encrypt the keys

B Each key belongs to exactly one hash slot

C There are 16,384 hash slots

D Hash slots help with cluster scaling

Hash slots do not encrypt keys; they only help distribute keys across nodes.

Explain how Redis Cluster uses hash slots to distribute keys across nodes.

Think about how Redis decides where to put each key in the cluster.

Describe what happens to hash slots and data when a Redis Cluster node fails.

Consider how Redis keeps the cluster working despite failures.