Hash slots distribution in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Hash slot calculation for a given key

Given the Redis key {user:1000}.data, what is the hash slot number assigned to this key in a Redis cluster?

A The hash slot is randomly assigned and not related to the key content.

B The hash slot is calculated on the entire key <code>{user:1000}.data</code> including the braces and suffix.

C The hash slot is always zero for keys with curly braces.

D The hash slot is calculated only on the substring inside curly braces, so the slot corresponds to the hash of <code>user:1000</code>.

💡 Hint

Redis cluster uses the substring inside curly braces to compute the hash slot.

Redis cluster uses the substring inside curly braces {} as the key for hash slot calculation. This allows grouping related keys in the same slot.

🧠 Conceptual

intermediate

Purpose of hash slots in Redis cluster

What is the main purpose of hash slots in a Redis cluster?

A To encrypt data stored in Redis for security.

B To compress keys to save memory space.

C To distribute keys evenly across multiple nodes for load balancing.

D To store keys in a single node only.

💡 Hint

Think about how Redis cluster manages data across nodes.

Hash slots allow Redis cluster to split the keyspace into 16384 slots, distributing them across nodes to balance load and enable scaling.

📝 Syntax

advanced

Identify the correct command to view hash slot allocation

Which Redis CLI command correctly shows the hash slot allocation for cluster nodes?

A CLUSTER SLOTS

B CLUSTER INFO

C CLUSTER NODES

D CLUSTER KEYSLOT <key>

💡 Hint

The command should show slot ranges assigned to nodes.

The CLUSTER SLOTS command returns the slot ranges and the nodes responsible for them.

🔧 Debug

advanced

Troubleshooting key slot mismatch error

You get a MOVED error when accessing a key in Redis cluster. What is the most likely cause?

A The client sent the key to the wrong node that does not own the key's hash slot.

B The key does not exist in the cluster.

C The key contains invalid characters.

D The Redis server is down.

💡 Hint

MOVED errors indicate redirection to the correct node.

A MOVED error means the client tried to access a key on a node that does not own the hash slot; the client should redirect to the correct node.

❓ optimization

expert

Optimizing multi-key operations with hash slots

You want to perform a multi-key operation (e.g., MGET) on keys user:1, user:2, and user:3 in a Redis cluster. How should you design the keys to ensure the operation succeeds without errors?

A Use completely different key names without curly braces.

B Use the same hash tag in curly braces for all keys, like <code>{user}:1</code>, <code>{user}:2</code>, <code>{user}:3</code>.

C Use keys with different hash tags, like <code>{user1}:1</code>, <code>{user2}:2</code>, <code>{user3}:3</code>.

D Use keys with no hash tags but ensure they are stored on the same node manually.

💡 Hint

Multi-key commands require keys to be in the same hash slot.

Using the same hash tag inside curly braces forces all keys to hash to the same slot, allowing multi-key commands to work.