KEYS pattern matching (avoid in production) in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What does the KEYS command return?

Given these keys in Redis: user:1, user:2, user:admin, session:1, session:2, what is the output of KEYS user:*?

Redis

KEYS user:*

A ["user:1", "user:2"]

B ["session:1", "session:2"]

C ["user:1", "user:2", "user:admin"]

D []

💡 Hint

The * wildcard matches any characters after 'user:'.

The KEYS command with pattern 'user:*' returns all keys starting with 'user:' including 'user:admin'.

🧠 Conceptual

intermediate

Why should KEYS be avoided in production?

Which of the following is the main reason to avoid using the KEYS command in a production Redis environment?

A It requires special permissions that are unsafe to grant.

B It deletes keys permanently without confirmation.

C It only works with string keys, not hashes or lists.

D It blocks the server and can cause latency spikes because it scans all keys.

💡 Hint

Think about what happens when KEYS scans a large database.

KEYS scans the entire keyspace which blocks Redis and can cause performance issues in production.

📝 Syntax

advanced

Which KEYS command pattern matches keys ending with ':id'?

You want to find all keys that end with ':id'. Which KEYS command pattern is correct?

A KEYS *id:

B KEYS *:id

C KEYS :id*

D KEYS id:*

💡 Hint

The * wildcard matches any characters before ':id'.

The pattern '*:id' matches any key ending with ':id'.

❓ optimization

advanced

How to safely find keys matching a pattern in production?

Since KEYS is unsafe in production, which Redis command is recommended to find keys matching a pattern without blocking the server?

A SCAN with MATCH option

B DEL with pattern

C GET with pattern

D EXPIRE with pattern

💡 Hint

This command iterates keys incrementally without blocking.

SCAN iterates keys in small batches and supports pattern matching with MATCH, avoiding blocking.

🔧 Debug

expert

What error occurs with invalid KEYS pattern?

What happens if you run KEYS user[ in Redis?

Redis

KEYS user[

A Syntax error due to incomplete pattern

B Returns an empty list because no keys match

C Returns all keys starting with 'user['

D Runtime error: invalid argument

💡 Hint

Check if the pattern syntax is correct.

The pattern 'user[' is incomplete and causes a syntax error in Redis.