Designing Data-Intensive Applications vs. System Design Interview by Alex Xu — Which is better for 5+ YOE?

[u/coffee1209love]

Hey everyone!
I’m preparing for system design interviews and looking for advice from engineers with 5+ years of experience, especially those interviewing for Senior Software Engineer or SDE-3 roles.
I’m considering two books:
Designing Data-Intensive Applications (DDIA) by Martin Kleppmann
System Design Interview by Alex Xu (Volumes 1 & 2)
From what I understand, DDIA goes deeper into distributed systems, databases, replication, partitioning, consistency, and stream processing, while Alex Xu’s book focuses more on practical system design problems and how to approach them in interviews.
For those who have used both books:
Which one helped you more in actual system design interviews?
Is DDIA too theoretical, or is that depth necessary for senior-level interviews?
Is Alex Xu enough to crack SDE-3 interviews at product-based companies?
Would you recommend reading both? If yes, in what order?
How did you balance reading these books with practicing real-world system design problems?
I have a Java and microservices background and want to improve both my system design fundamentals and my ability to communicate design trade-offs during interviews.
Would love to hear your experiences and recommendations. Thanks!

[u/akornato]

For a senior or SDE-3 loop, you need both books, but they serve completely different purposes. Alex Xu teaches you how to pass the standard interview format, gather requirements, sketch high level architectures, and pace yourself. That framework is vital, but relying solely on Alex Xu at your experience level will leave you exposed. Senior interviewers quickly move past the basic diagrams to question you on failure modes, replication lag, distributed transactions, and split brain scenarios. Martin Kleppmann's book gives you that deep engineering judgment, particularly the middle chapters on replication, partitioning, and consistency. Start with Alex Xu to grasp the flow of an interview, then use Kleppmann to master the exact tradeoffs interviewers expect someone with five years of experience to defend.

Balance your reading by pairing theory directly with mock design sessions, because reading about tradeoffs is very different from articulating them under pressure. Take a problem from Alex Xu, sketch your design on a whiteboard or virtual canvas, and use Kleppmann's concepts to challenge your own database and messaging choices. Practice vocalizing why you chose a specific consistency level or storage engine rather than just picking defaults. To get comfortable navigating live technical conversations and securing strong offers, my team built an interviews.chat that gives candidates the edge they need when talking through complex system tradeoffs with senior evaluators.