EXPIRE and TTL for time-to-live in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the TTL after setting EXPIRE?

You run the following Redis commands:

SET session:user123 "active"
EXPIRE session:user123 120

What will TTL session:user123 return immediately after?

Redis

SET session:user123 "active"
EXPIRE session:user123 120
TTL session:user123

A 120

B -1

C -2

D 0

💡 Hint

TTL returns the remaining time in seconds before the key expires.

After setting EXPIRE with 120 seconds, TTL returns the remaining seconds, which is 120 immediately after.

❓ query_result

intermediate

What does TTL return for a key without expiration?

If you run:

SET config:theme "dark"

and then:

TTL config:theme

What is the expected output?

Redis

SET config:theme "dark"
TTL config:theme

A -1

B 0

C -2

D null

💡 Hint

TTL returns -1 if the key exists but has no expiration.

TTL returns -1 when the key exists but does not have an expiration time set.

📝 Syntax

advanced

Which EXPIRE command syntax is correct?

Which of the following Redis commands correctly sets a key to expire in 60 seconds?

A EXPIRE 60 mykey

B EXPIRE mykey TO 60

C EXPIRE mykey 60

D EXPIRE mykey EX 60

💡 Hint

The EXPIRE command syntax is: EXPIRE key seconds

The correct syntax is EXPIRE followed by the key and then the number of seconds.

❓ query_result

advanced

What happens to TTL after key deletion?

You run:

SET temp:data "123"
EXPIRE temp:data 30
DEL temp:data

What will TTL temp:data return after deletion?

Redis

SET temp:data "123"
EXPIRE temp:data 30
DEL temp:data
TTL temp:data

A -1

B -2

C 0

D 30

💡 Hint

TTL returns -2 if the key does not exist.

After deleting the key, it no longer exists, so TTL returns -2.

🧠 Conceptual

expert

Why use EXPIRE instead of manual deletion?

Which is the main advantage of using EXPIRE to set a time-to-live on keys instead of manually deleting keys later?

A EXPIRE makes keys immutable until expiration.

B EXPIRE duplicates keys to backup storage before deletion.

C EXPIRE encrypts keys for security until they expire.

D EXPIRE automatically removes keys after a set time, reducing memory usage without manual intervention.

💡 Hint

Think about automation and resource management.

EXPIRE automates key removal after a set time, helping manage memory efficiently without manual cleanup.