HardSystem designSystem design30 min to answer

Design a production RAG system for ten million documents.

1Give yourself 30 minutes

2Answer out loud, not in your head

3Then compare with the answer below

Stuck? Show a way to structure it+

01Clarify the objective, user, constraints, and acceptable failure modes.
02Structure the response around ingestion, hybrid retrieval, reranking, evaluation.
03Compare credible alternatives and state the decision criteria.
04Finish with validation, monitoring, and what would change the decision.

Reference answer

strong answer

I would first define the outcome and acceptable error boundary. I would explicitly cover ingestion, hybrid retrieval, reranking, evaluation. I would select an approach only after comparing quality, latency, cost, safety, and operational complexity, then validate it with representative cases and production monitoring.

ingestion
hybrid retrieval
reranking
evaluation

Must be adapted to the interviewer’s scenario
Would benefit from concrete numbers and personal examples

alternative answer

A second valid approach is to begin with the highest-risk assumption and test it cheaply. I would explicitly cover ingestion, hybrid retrieval, reranking, evaluation. I would select an approach only after comparing quality, latency, cost, safety, and operational complexity, then validate it with representative cases and production monitoring.

ingestion
hybrid retrieval
reranking
evaluation

Must be adapted to the interviewer’s scenario
Would benefit from concrete numbers and personal examples

Grade yourself

ingestion

weight 30%

StrongExplains ingestion concretely and ties it to a decision or measurable outcome.

WeakMentions ingestion without implications, trade-offs, or evidence.

hybrid retrieval

weight 25%

StrongExplains hybrid retrieval concretely and ties it to a decision or measurable outcome.

WeakMentions hybrid retrieval without implications, trade-offs, or evidence.

reranking

weight 25%

StrongExplains reranking concretely and ties it to a decision or measurable outcome.

WeakMentions reranking without implications, trade-offs, or evidence.

evaluation

weight 20%

StrongExplains evaluation concretely and ties it to a decision or measurable outcome.

WeakMentions evaluation without implications, trade-offs, or evidence.

Then expect these follow-ups

Where is the first bottleneck at 10× traffic?
Tests: depth
What are the main failure modes?
Tests: adaptability
How would you roll this out safely?
Tests: adaptability

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