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Google·Software Engineer·Onsite - System Design / Architecture·Senior

SeniorPrefer not to say
Apr 2026

Summary

Google system design round for a software engineering role. The question was one big pipeline design problem and they just let it run for the full hour, which I wasn't totally ready for.

Questions Asked (1)

Q1

Design a data pipeline that reads many text files of varying sizes and produces output files of exactly 100 MB each. The output must preserve line boundaries, include every input line exactly once, and handle concerns like partial lines at chunk boundaries, buffering strategy, compression, parallelism, and fault tolerance with exactly-once semantics.

System DesignTechnical Trade-offsAlgorithms & Data Structures
Author's notes

This wrecked me a little.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and constraints, then propose a high-level architecture that separates reading, processing, and writing stages. Focus on how to handle line boundaries and exactly-once semantics, and discuss trade-offs between parallelism, buffering, and compression.

Pro tip: Emphasize idempotency and checkpointing to achieve exactly-once semantics, and consider using a distributed file system like Google Cloud Storage with a manifest-based approach to track processed files.

1. Clarify Requirements and Constraints

Ask about input size, file distribution, expected output, and any specific technologies (e.g., GFS, MapReduce). Confirm that output files must be exactly 100 MB and that line boundaries must be preserved.

2. Design High-Level Architecture

Propose a pipeline with three stages: reading input files, processing lines into 100 MB chunks, and writing output files. Consider using a distributed processing framework like MapReduce or Apache Beam.

3. Address Line Boundaries and Buffering

Explain how to handle partial lines at chunk boundaries by buffering incomplete lines and carrying them over to the next chunk. Discuss buffer size trade-offs and the need to flush buffers at the end.

4. Ensure Exactly-Once Semantics and Fault Tolerance

Describe mechanisms like idempotent writes, checkpointing, and transactional writes to guarantee exactly-once processing. Discuss how to recover from failures without duplicating or losing lines.

5. Discuss Parallelism and Compression

Explain how to parallelize reading and writing while maintaining output file size constraints. Discuss compression options (e.g., gzip) and their impact on file size and processing.

Key Points to Mention

  • Handling partial lines at chunk boundaries by buffering and carrying over incomplete lines.
  • Exactly-once semantics via idempotent writes, checkpointing, and transactional writes.
  • Parallelism strategies: partitioning input files and coordinating output file sizes.
  • Buffering strategy: trade-offs between memory usage and I/O efficiency.
  • Compression: using gzip or similar, and ensuring compressed files are exactly 100 MB if required.
  • Fault tolerance: replication, retries, and recovery from failures without data loss or duplication.

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