Notification system design in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Identify the correct component for handling user preferences in a notification system

In a notification system, users can choose how they want to receive notifications (email, SMS, push). Which component is best suited to manage these preferences?

A Notification Dispatcher

B Message Queue

C Notification Logger

D User Preference Service

💡 Hint

Think about where user choices are stored and accessed before sending notifications.

The User Preference Service stores and manages user notification settings, ensuring notifications are sent according to user choices.

❓ scaling

intermediate

Scaling the notification delivery to millions of users

You need to design a notification system that can send push notifications to 10 million users simultaneously. Which approach best supports this scale?

A Use a distributed message queue with multiple worker services sending notifications in parallel

B Use a single server to send all notifications sequentially

C Send notifications directly from the database triggers

D Store notifications in a file and send them manually

💡 Hint

Consider how to handle large volumes efficiently and avoid bottlenecks.

A distributed message queue with multiple workers allows parallel processing and scales horizontally to handle millions of notifications efficiently.

❓ tradeoff

advanced

Choosing between push and pull notification models

Which is a key tradeoff when choosing between push and pull notification delivery models?

A Push notifications require clients to request updates; pull notifications send updates automatically

B Push notifications reduce server load but increase client battery usage; pull notifications increase server load but save client battery

C Push notifications are slower than pull notifications in delivering messages

D Pull notifications cannot be used for mobile devices

💡 Hint

Think about who initiates the communication and resource usage on client and server.

Push notifications are sent by the server, which can reduce server polling but may increase client battery use. Pull requires clients to poll, increasing server load but saving client battery.

🧠 Conceptual

advanced

Ensuring message ordering in a distributed notification system

In a distributed notification system, what is the best way to ensure notifications are delivered to a user in the order they were generated?

A Send notifications from multiple servers without coordination

B Store notifications in a database without timestamps

C Use a single partitioned message queue per user to preserve order

D Deliver notifications randomly to reduce latency

💡 Hint

Think about how message queues can preserve order per user.

Using a single partitioned queue per user ensures messages are processed in the order they arrive, preserving notification order.

❓ estimation

expert

Estimating storage needs for notification logs

Your notification system logs every notification sent. Each log entry is 1 KB. If you send 1 million notifications per day and keep logs for 90 days, how much storage do you need?

A Approximately 90 GB

B Approximately 9 GB

C Approximately 900 GB

D Approximately 9000 GB

💡 Hint

Calculate total entries times size per entry.

1 million notifications/day * 90 days = 90 million entries. 90 million * 1 KB = 90 million KB = 90 GB.