SETNX for set-if-not-exists in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command SETNX do?

SETNX sets a key to a value only if the key does not already exist in the database.

beginner

What will SETNX mykey "hello" return if mykey already exists?

It will return 0, meaning the key was not set because it already exists.

intermediate

How can SETNX be useful in real-life applications?

It can be used to create locks or ensure a value is set only once, like setting a unique user ID or a one-time token.

beginner

What is the difference between SET and SETNX in Redis?

SET always sets the key to the value, overwriting if it exists. SETNX sets the key only if it does not exist.

beginner

If SETNX returns 1, what does that mean?

It means the key was successfully set because it did not exist before.

What does the Redis command SETNX key value do?

A Deletes the key if it exists

B Always sets the key to the value

C Returns the current value of the key

D Sets the key only if it does not exist

SETNX means 'set if not exists'. It sets the key only if it does not already exist.

What does SETNX return if the key already exists?

A null

B 1

C 0

D error

SETNX returns 0 if the key already exists and the value was not set.

Which Redis command would you use to set a key only if it does not exist?

A GET

B SETNX

C SET

D DEL

SETNX is designed to set a key only if it does not exist.

Why might you use SETNX in a distributed system?

A To create a lock preventing race conditions

B To get the value of a key

C To always overwrite values

D To delete keys safely

SETNX can be used to create locks by setting a key only if it does not exist, preventing multiple clients from doing the same action simultaneously.

If you want to set a key regardless of its existence, which command should you use?

A SET

B SETNX

C GET

D EXISTS

SET sets the key value no matter if the key exists or not.

Explain how the Redis command SETNX works and give an example of when you might use it.

Think about setting a value only once.

What is the difference between SET and SETNX in Redis?

Consider what happens if the key already exists.