Client-side cluster support in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis cluster command?

Consider a Redis cluster with 3 nodes. You run the command CLUSTER NODES. What kind of information does this command return?

Redis

CLUSTER NODES

A The cluster configuration file contents.

B Only the master nodes' IP addresses and ports.

C A list of all nodes in the cluster with their IDs, IP addresses, ports, roles, and slot ranges.

D The current key-value pairs stored in the cluster.

💡 Hint

Think about what information is needed to understand the cluster topology.

The CLUSTER NODES command returns detailed info about all nodes in the cluster, including their IDs, IPs, roles (master/slave), and the slots they serve.

🧠 Conceptual

intermediate

How does client-side cluster support handle key distribution?

In Redis client-side cluster support, how does the client decide which node to send a command to for a given key?

A The client calculates the hash slot of the key and sends the command to the node responsible for that slot.

B The client sends the command to a random node and lets the cluster redirect it.

C The client always sends commands to the master node only.

D The client broadcasts the command to all nodes and waits for the first response.

💡 Hint

Think about how the cluster divides keys among nodes.

Client-side cluster support uses a hash function to compute the slot for a key and sends commands directly to the node responsible for that slot, avoiding redirections.

📝 Syntax

advanced

Which Redis command syntax correctly requests a slot migration in a cluster?

You want to migrate slot 1000 from one node to another in a Redis cluster. Which command syntax is correct?

A CLUSTER SETSLOT 1000 MIGRATING <node-id>

B CLUSTER MIGRATE SLOT 1000 TO <node-id>

C CLUSTER SETSLOT MIGRATING 1000 <node-id>

D CLUSTER SLOT MIGRATE 1000 <node-id>

💡 Hint

Check the official Redis cluster command format for SETSLOT.

The correct syntax is CLUSTER SETSLOT <slot> MIGRATING <node-id> to mark a slot as migrating.

❓ optimization

advanced

How can client-side cluster support reduce redirections during key access?

Which approach best reduces the number of redirections a Redis client experiences when accessing keys in a cluster?

A The client always queries a random node to get the latest cluster slots mapping before each command.

B The client caches the cluster slots mapping and updates it only when a MOVED or ASK error occurs.

C The client sends all commands to the cluster's master node to avoid redirections.

D The client disables cluster mode and treats the cluster as a single node.

💡 Hint

Think about how clients can remember cluster topology to avoid unnecessary redirects.

Caching the slots mapping locally allows the client to send commands directly to the right node, reducing redirections.

🔧 Debug

expert

Why does this Redis cluster client command cause a MOVED error?

A client sends the command GET user:123 to a Redis cluster node but receives a MOVED error pointing to another node. What is the most likely cause?

Redis

GET user:123

A The client sent the command with an invalid syntax.

B The key user:123 does not exist in the cluster.

C The cluster is down and cannot process commands.

D The client has an outdated slots cache and sent the command to the wrong node.

💡 Hint

Consider what MOVED errors indicate in Redis cluster communication.

A MOVED error means the client sent the command to a node that no longer owns the slot for the key, usually due to outdated slot cache.