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Snap·Machine Learning Engineer·Onsite - System Design / Architecture·Senior

Senior
May 2026

Summary

Had a system design round at Snap for an ML engineer role, and the whole thing basically came down to one meaty question about RAG chunking strategy. Not what I expected to spend 45 minutes on, but here we are.

Questions Asked (1)

Q1

How would you design an effective chunking strategy for information in a RAG system?

System DesignTechnical Trade-offs
Author's notes

I went straight into fixed-size vs semantic chunking and talked about overlap windows, which felt solid at first.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the use case and data types, then propose a chunking strategy that balances retrieval granularity and context preservation. Discuss trade-offs between chunk size, overlap, and metadata, and how to evaluate and iterate based on retrieval metrics.

Pro tip: Emphasize that chunking should be driven by the downstream task and retrieval evaluation; avoid one-size-fits-all and consider dynamic or hierarchical chunking for heterogeneous data.

1. Understand the Data and Use Case

Identify the types of documents (e.g., short messages, long articles, code) and the retrieval tasks (e.g., question answering, summarization). This informs the appropriate granularity and structure.

2. Choose a Chunking Method

Select from fixed-size, semantic, recursive, or hierarchical chunking based on data characteristics. Consider using overlap to preserve context across boundaries.

3. Optimize Chunk Size and Overlap

Experiment with different sizes and overlaps, using retrieval metrics (e.g., recall@k, MRR) to find the sweet spot that balances precision and context.

4. Enrich with Metadata

Attach metadata (e.g., source, timestamp, section headers) to chunks to enable filtering and improve retrieval relevance.

5. Evaluate and Iterate

Set up an evaluation pipeline with human or automated judgments to continuously refine the chunking strategy as data and queries evolve.

Key Points to Mention

  • Trade-offs between chunk size and retrieval performance (precision vs. recall)
  • Importance of overlap to maintain context across chunk boundaries
  • Semantic vs. fixed-size chunking and when to use each
  • Metadata enrichment for filtering and improved relevance
  • Evaluation metrics and iterative refinement
  • Handling heterogeneous data with dynamic or hierarchical chunking

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.