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

An e-commerce platform uses Cloud Spanner as its database. The orders table has a monotonically increasing order_id as the primary key, and the team observes high write latency during peak hours. Which design change would BEST distribute write load across nodes?

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

Change the primary key to a UUID string

Using a UUID (or a hash prefix) as the primary key or as a leading part of a composite key prevents hotspotting on a single tablet server by distributing writes across the cluster.

Answer analysis

Option-by-option breakdown

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

  • Add a secondary index on order_id

    Why it's wrong here

    Secondary indexes do not affect the primary key distribution of writes.

  • Increase the number of nodes

    Why it's wrong here

    More nodes help with throughput but don't fix the hotspotting caused by monotonically increasing keys.

  • Use interleaving with a parent table

    Why it's wrong here

    Interleaving is for locality and does not solve the hotspotting of a monotonic key.

  • Change the primary key to a UUID string

    Why this is correct

    UUIDs are random, distributing writes evenly across nodes and avoiding hotspots.

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Last reviewed: Jul 4, 2026

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