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PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions

You are migrating a relational database to Cloud Bigtable. The source schema has a Users table and an Orders table with a one-to-many relationship. The application frequently queries all orders for a user. Which three Bigtable schema design practices should you apply?

⚠ Common exam trap

Google often tests the misconception that relational normalization principles apply to NoSQL databases, but in Bigtable, denormalization and row-key design are critical for performance, and maintaining foreign keys or 3NF leads to inefficient scans and poor latency.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

Denormalize by storing orders as multiple columns or a serialized column in the Users row

Cloud Bigtable is a wide-column NoSQL database that does not support joins. To efficiently query all orders for a user, you must denormalize the one-to-many relationship by storing orders as multiple columns (e.g., order_1, order_2) or as a serialized JSON/protobuf column within the user's row. This avoids the need for a separate lookup or join, enabling single-row reads for the user's orders.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

  • Denormalize by storing orders as multiple columns or a serialized column in the Users row

    Why this is correct

    Denormalization avoids joins; storing orders within the user row allows single-row reads for all orders.

  • Maintain 3NF to avoid data duplication

    Why it's wrong here

    Bigtable is NoSQL; normalization is counterproductive — denormalization is recommended.

  • Use a row key that includes a hash prefix to distribute writes

    Why this is correct

    Salting prevents hotspots when rows are inserted in order.

  • Keep the foreign key relationship by storing UserId in the Orders row key

    Why it's wrong here

    This still requires multiple row reads for a user's orders; denormalization is preferred.

  • Create a separate column family for user attributes and orders

    Why this is correct

    Column families help organize data and can be optimized for different access patterns.

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Last reviewed: Jul 4, 2026

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