Session storage pattern in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis command sequence?

Given these Redis commands executed in order:

1. SET session:123 user1
2. EXPIRE session:123 10
3. TTL session:123

What does the TTL command return immediately after setting the expiration?

Redis

SET session:123 user1
EXPIRE session:123 10
TTL session:123

A -2

B -1

C 10

D 0

💡 Hint

TTL returns the remaining time to live in seconds for a key with expiration.

After setting an expiration of 10 seconds, TTL returns the remaining seconds before the key expires, which is 10 immediately after setting.

📝 Syntax

intermediate

Which Redis command syntax correctly stores a session with a 30-minute expiration?

You want to store a session key 'session:456' with value 'user2' that expires in 30 minutes. Which command is correct?

A SETEX session:456 1800 user2

B SET session:456 user2 EX 1800

C SET session:456 user2 PX 1800000

D EXPIRE session:456 1800 SET user2

💡 Hint

SETEX sets a key with expiration in seconds in one command.

SETEX key seconds value sets the key with expiration in seconds. Option A uses correct syntax.

❓ optimization

advanced

Which approach optimizes session storage for frequent updates in Redis?

You store user sessions in Redis and update session data frequently. Which approach is best to optimize performance and reduce network overhead?

A Store session data as a Redis hash and update fields with HSET commands

B Store session data as a JSON string and overwrite with SET on every update

C Store session data in multiple keys per field and update keys individually

D Store session data in a Redis list and push updates to the list

💡 Hint

Hashes allow updating parts of data without rewriting the whole value.

Using Redis hashes lets you update individual fields efficiently, reducing data transfer and improving performance.

🔧 Debug

advanced

Why does this Redis session expiration not work as expected?

You run these commands:
1. SET session:789 user3
2. EXPIRE session:789 60
3. SET session:789 user3_updated

After 60 seconds, the key still exists. Why?

Redis

SET session:789 user3
EXPIRE session:789 60
SET session:789 user3_updated

A The key was deleted before expiration

B EXPIRE command was not executed correctly

C Redis does not support expiration on string keys

D The last SET command removes the expiration from the key

💡 Hint

Setting a key again resets its expiration unless specified.

A new SET command without expiration removes any previous expiration on the key.

🧠 Conceptual

expert

What is the main advantage of using Redis session storage over traditional database sessions?

Why do many web applications prefer Redis for session storage instead of storing sessions in a traditional relational database?

A Redis supports complex SQL queries on session data

B Redis provides faster read/write performance due to in-memory storage

C Redis sessions never expire unless manually deleted

D Redis automatically encrypts session data for security

💡 Hint

Think about speed and how Redis stores data.

Redis stores data in memory, making session reads and writes much faster than disk-based databases.