Read replicas in HLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a read replica in database systems?

A read replica is a copy of the primary database that handles read-only queries to reduce load on the primary and improve read scalability.

beginner

How do read replicas improve system performance?

They distribute read traffic across multiple copies, reducing the load on the primary database and allowing more users to read data simultaneously.

intermediate

What is eventual consistency in the context of read replicas?

Eventual consistency means that changes made on the primary database take some time to appear on read replicas, so reads might be slightly out-of-date temporarily.

intermediate

Name one common challenge when using read replicas.

One challenge is replication lag, where the read replica is behind the primary, causing stale data to be served to users.

intermediate

Why might a system use multiple read replicas instead of just one?

Multiple read replicas allow better load balancing, higher availability, and fault tolerance for read operations.

What type of queries are typically sent to read replicas?

A Schema changes

B Write queries

C Read-only queries

D Backup operations

Read replicas handle read-only queries to reduce load on the primary database.

What is a common downside of using read replicas?

A Replication lag causing stale reads

B Increased write latency

C Higher cost for write operations

D Loss of data durability

Replication lag means read replicas may serve slightly outdated data temporarily.

Which of the following best describes eventual consistency?

A Data changes propagate to replicas after some delay

B Data is consistent only on the primary

C Data is never consistent across replicas

D Data is always immediately consistent across replicas

Eventual consistency means data changes appear on replicas after a short delay.

Why use multiple read replicas?

A To improve write speed

B To balance read load and increase availability

C To reduce storage costs

D To simplify schema migrations

Multiple replicas help distribute read traffic and provide fault tolerance.

Which component usually handles directing read queries to replicas?

A Write coordinator

B Primary database

C Backup service

D Load balancer or query router

A load balancer or query router directs read queries to replicas to balance load.

Explain what read replicas are and how they help scale database systems.

Think about how copying data helps many users read at the same time.

Describe the challenges and trade-offs when using read replicas in a system.

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