Real-time notification pattern in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis PUBSUB CHANNELS command?

Assume two clients subscribe to channels 'news' and 'sports'. What does the command PUBSUB CHANNELS return?

Redis

PUBSUB CHANNELS

A ["news", "sports"]

B ["news"]

C []

D ["news", "sports", "weather"]

💡 Hint

PUBSUB CHANNELS lists all active channels with subscribers.

The PUBSUB CHANNELS command returns all channels that have at least one subscriber. Since clients subscribed to 'news' and 'sports', these two channels appear.

🧠 Conceptual

intermediate

Which Redis data structure is best for storing user notification preferences in a real-time system?

You want to store which types of notifications each user wants to receive. Which Redis data structure fits best?

A Sorted Set

B Set

C List

D Hash

💡 Hint

Think about storing multiple key-value pairs per user.

A Hash allows storing multiple fields and values per user, such as notification types and preferences, making it efficient for this use case.

📝 Syntax

advanced

Which Redis command syntax correctly publishes a message to a channel?

Select the correct syntax to publish the message 'Hello' to the channel 'updates'.

A PUBLISH updates Hello

B PUBLISH 'updates' 'Hello'

C PUBLISH updates 'Hello'

D PUBLISH 'updates' Hello

💡 Hint

Redis commands do not require quotes for simple strings.

The correct syntax is PUBLISH updates Hello. Redis commands take arguments without quotes unless the argument contains spaces or special characters.

❓ optimization

advanced

How to optimize Redis Pub/Sub for high message throughput?

You have many subscribers and high message volume. Which approach improves Redis Pub/Sub performance?

A Use a single Redis instance with many channels

B Use multiple Redis instances with sharded channels

C Use Redis transactions for publishing messages

D Use Redis sorted sets to queue messages

💡 Hint

Distributing load helps handle more messages.

Sharding channels across multiple Redis instances spreads the load and improves throughput by parallelizing message delivery.

🔧 Debug

expert

Why does this Redis Pub/Sub subscriber not receive messages?

A client runs SUBSCRIBE news but never receives messages published to 'news'. What is the likely cause?

Redis

Client 1: SUBSCRIBE news
Client 2: PUBLISH news "Hello"

A Client 2 used wrong channel name in PUBLISH

B Redis server is down

C Client 1 subscribed after Client 2 published the message

D Client 1 did not run SUBSCRIBE command correctly

💡 Hint

Messages published before subscription are not received.

Redis Pub/Sub delivers messages only to clients subscribed at the time of publishing. If Client 1 subscribed after Client 2 published, it misses the message.