Read replicas in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the primary purpose of read replicas

What is the main reason to use read replicas in a database system?

A To reduce network latency by storing data closer to users

B To provide backup storage for disaster recovery only

C To increase the write throughput by distributing write operations

D To improve read scalability by distributing read operations

💡 Hint

Think about how read replicas help when many users want to access data simultaneously.

Read replicas are primarily used to distribute read requests, improving read scalability and reducing load on the primary database.

❓ Architecture

intermediate

Choosing the correct architecture for read replicas

Which architecture best describes a system using read replicas to handle high read traffic?

A One primary database handling writes and multiple read replicas handling read queries

B Multiple primary databases each handling a subset of writes and reads independently

C Multiple read replicas handling writes and a primary database handling reads

D A single primary database handling all reads and writes with no replicas

💡 Hint

Consider which node handles writes and which nodes handle reads in a typical read replica setup.

In a read replica architecture, the primary database handles all writes, while read replicas serve read queries to scale read capacity.

❓ scaling

advanced

Scaling read replicas for global users

You have a global user base with users in multiple continents. How should you deploy read replicas to minimize read latency?

A Deploy read replicas only in the primary database region to keep data consistent

B Deploy read replicas in multiple geographic regions close to user clusters

C Deploy read replicas randomly without considering user location

D Use a single read replica in a central location with the fastest network

💡 Hint

Think about how placing data closer to users affects latency.

Deploying read replicas geographically close to users reduces network latency and improves read performance globally.

❓ tradeoff

advanced

Tradeoffs of using read replicas for strong consistency

What is a common tradeoff when using read replicas in systems that require strong consistency?

A Read replicas may serve stale data due to replication lag

B Read replicas always provide up-to-date data with no delay

C Read replicas improve write performance by delaying replication

D Read replicas eliminate the need for a primary database

💡 Hint

Consider what happens when data changes on the primary but replicas have not yet updated.

Replication lag means read replicas might not have the latest data immediately, causing potential stale reads.

❓ estimation

expert

Estimating read replica capacity for a high-traffic system

Your system receives 10,000 read requests per second and 1,000 write requests per second. Each read replica can handle 2,000 reads per second. How many read replicas do you need to handle the read load without overloading the primary?

A 4 read replicas

B 10 read replicas

C 5 read replicas

D 6 read replicas

💡 Hint

Divide total read requests by capacity per replica and round up.

To handle 10,000 reads per second with each replica handling 2,000, you need 10,000 / 2,000 = 5 replicas.