Design innovative, scalable, and highly available cloud database solutions →mediumMultiple ChoiceObjective-mapped
PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
A company is running a financial application on Cloud Spanner and needs to ensure strong transactional consistency across regions. The application requires both high write throughput (2000 mutations/second) and read throughput (2000 reads/second). According to Spanner capacity planning, how many processing units (PUs) are needed for the combined workload?
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
✓
1 processing unit (PU)
Spanner capacity: write throughput 2000 mutations/second per PU, read throughput 2000 reads/second per PU. For 2000 writes/s and 2000 reads/s, you need 1 PU for writes and 1 PU for reads, but the reads and writes share the same PU. Actually, the formula is: PUs needed = max(write_throughput/2000, read_throughput/2000). For 2000 each, that's max(1,1)=1 PU. However, the question states 'high write throughput (2000 mutations/second) and read throughput (2000 reads/second)'. So 1 PU is sufficient. But note: in practice, you might need more for other factors. The question tests the calculation. The answer is 1 PU.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
2 processing units (PUs)
Why it's wrong here
2 PUs would provide 4000 writes/s and 4000 reads/s, which is more than needed.
- ✗
4 processing units (PUs)
Why it's wrong here
4 PUs provide 8000 writes/s and reads/s, far exceeding requirements.
- ✗
0.5 processing units (PUs)
Why it's wrong here
PUs are indivisible; minimum is 1.
- ✓
1 processing unit (PU)
Why this is correct
One PU provides 2000 writes/s and 2000 reads/s, exactly matching the requirement.
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