Interview Foundations
How to run a design conversation, calculate scale and sizing, and pick a consistency model you can defend.
Running a Design Interview
A design round is 45 minutes and nobody grades the diagram alone. They grade how you scope, size, sketch, go deep and own your tradeoffs. Here is a sequence I have used and coached, with a full IRCTC Tatkal walk-through and a clock you can actually follow.
Capacity Estimation and System Sizing
How to size servers, storage, databases, and caches in five minutes. Stating your assumptions, calculating peak QPS, and defending your architecture with simple arithmetic.
API Contract and Data Model
Write down the requests and responses first, then the entities, then the keys that make your common queries one lookup. IDs, retries, pagination and error codes are where most designs quietly go wrong.
CAP and Consistency, Honestly
When the network between your data centres breaks, you either refuse some requests or accept answers that may be wrong. Everything else on this page is about picking which one, per feature, and saying it clearly.
SQL vs NoSQL Without the Religion
The honest question is never "which database is better". It is what shape your data has, how you will read it, and which writes must never be wrong. Start with Postgres, and learn what would make you leave.
Database Types Field Guide
Seven families of database, each built to answer one kind of question fast. This page tells you the question each one is good at, how each one breaks, and how to pick without arguing for an hour.