Notification system in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Design components for a scalable notification system

You need to design a notification system that can send alerts via email, SMS, and push notifications. Which component is essential to handle different notification types efficiently?

A A client-side script that sends notifications directly to users

B A single database table storing all notification logs without separation

C A unified notification dispatcher that routes messages to specific channels

D A monolithic service that sends all notifications synchronously

💡 Hint

Think about how to separate concerns for different notification channels.

A unified dispatcher allows the system to route notifications to the correct channel efficiently, supporting scalability and maintainability.

❓ scaling

intermediate

Estimating capacity for peak notification loads

Your notification system must handle 10,000 notifications per second during peak hours. What is the best approach to estimate the required throughput capacity?

A Ignore peak loads and design for average daily notifications

B Use the total number of users multiplied by 10 without considering delivery time

C Estimate capacity by the number of developers working on the system

D Calculate based on average notification size, delivery latency, and concurrency limits of each channel

💡 Hint

Consider factors that affect how many notifications can be sent per second.

Estimating throughput requires understanding message size, delivery latency, and concurrency limits to ensure the system can handle peak loads without delays.

❓ tradeoff

advanced

Choosing between push and pull notification models

Which tradeoff is true when choosing a push-based notification system over a pull-based one?

A Pull delivers notifications instantly without server overhead

B Push reduces client polling but requires maintaining persistent connections, increasing server resource use

C Push requires clients to poll frequently, increasing network traffic

D Pull requires servers to push messages directly to clients

💡 Hint

Think about how push and pull models handle message delivery and resource usage.

Push notifications reduce client polling but need persistent connections, which use more server resources. Pull models rely on client polling, increasing network traffic.

🧠 Conceptual

advanced

Ensuring message delivery guarantees in notification systems

Which mechanism best ensures 'at least once' delivery guarantee for notifications?

A Use message queues with acknowledgments and retries on failure

B Send notifications without tracking delivery status

C Deliver notifications only once without retries

D Use fire-and-forget messaging without persistence

💡 Hint

Consider how to handle failures and retries to avoid lost messages.

Message queues with acknowledgments and retries ensure messages are delivered at least once, even if failures occur during transmission.

❓ component

expert

Designing a notification throttling mechanism

You want to prevent users from receiving more than 5 notifications per minute. Which component design best enforces this throttling?

A A rate limiter that tracks notification counts per user and blocks excess sends

B A database trigger that deletes notifications after 5 per minute

C A client-side script that ignores notifications after 5 per minute

D A logging service that records notifications without blocking

💡 Hint

Think about where and how to enforce limits to control notification flow.

A rate limiter component tracks how many notifications each user receives and blocks sending more than the allowed limit, ensuring throttling is enforced server-side.