Multi-key operations in cluster in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a key limitation of multi-key operations in a Redis cluster?

Multi-key operations can only be performed on keys that are in the same hash slot. Keys in different slots cannot be used together in a single multi-key command.

beginner

How does Redis cluster determine which keys belong to the same hash slot?

Redis cluster uses a hash function on the key name or a part of it (called a hash tag) to assign keys to one of 16384 hash slots. Keys with the same hash slot number are stored on the same node.

intermediate

What is a hash tag in Redis cluster multi-key operations?

A hash tag is a substring enclosed in curly braces {} within a key name. It forces Redis to use only that substring for hashing, allowing multiple keys with the same hash tag to be in the same slot.

intermediate

Why can't you run a command like MGET on keys in different hash slots in Redis cluster?

Because Redis cluster distributes keys across nodes by hash slots, multi-key commands require all keys to be on the same node. Different slots mean keys are on different nodes, so the command would fail.

intermediate

How can you design keys to enable multi-key operations in Redis cluster?

Use hash tags by including the same substring in curly braces in all related keys. This ensures they hash to the same slot and can be used together in multi-key commands.

In Redis cluster, what must be true for keys used in a multi-key command like MGET?

A Keys must be on different nodes

B Keys can be in any hash slot

C All keys must be in the same hash slot

D Keys must have different hash tags

Multi-key commands require all keys to be in the same hash slot so they reside on the same node.

What is the purpose of a hash tag in Redis cluster keys?

A To encrypt the key

B To force keys to the same hash slot

C To make keys unique

D To store keys on different nodes

Hash tags force Redis to hash only the substring inside curly braces, placing keys with the same tag in the same slot.

How many hash slots does a Redis cluster have?

A 16384

B 8192

C 1024

D 32768

Redis cluster uses 16384 hash slots to distribute keys across nodes.

What happens if you try to run a multi-key command on keys in different hash slots in Redis cluster?

A The command succeeds normally

B The command runs but returns partial results

C The command merges keys automatically

D The command fails with a CROSSSLOT error

Redis cluster returns a CROSSSLOT error because multi-key commands require keys in the same slot.

Which of these keys will be in the same hash slot in Redis cluster?

A user:{1000}:name and user:{1000}:email

B user:{1000} and user:{1001}

C user:1000 and user:{1001}

D user:1000 and user:1001

Keys with the same hash tag inside curly braces hash to the same slot.

Explain why multi-key operations in Redis cluster require keys to be in the same hash slot and how hash tags help achieve this.

Think about how Redis cluster splits data and how hash tags control key placement.

Describe how you would design keys to support multi-key commands like MGET in a Redis cluster environment.

Focus on key naming patterns that control hash slot assignment.