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

A company is planning to use Cloud Spanner for a new global application. They estimate a peak write throughput of 10,000 mutations per second. What is the minimum number of processing units (PUs) required, given that each PU supports up to 2000 mutations/second?

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

5 processing units

Each PU supports 2000 mutations/second. To get 10,000 mutations/second, you need 10,000 / 2000 = 5 PUs. However, note that Spanner also requires at least 1 node (1000 PUs) for production. But the question asks for PUs based on write throughput alone.

Answer analysis

Option-by-option breakdown

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

  • 1 processing unit

    Why it's wrong here

    1 PU provides only 2000 mutations/second.

  • 5 processing units

    Why this is correct

    5 PUs provide 10,000 mutations/second.

  • 100 processing units

    Why it's wrong here

    Way too high; 100 PUs would provide 200,000 mutations/second.

  • 10 processing units

    Why it's wrong here

    10 PUs would provide 20,000 mutations/second, more than needed.

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Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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