The answer is write throughput in queries per second (QPS). Cloud Spanner node capacity is directly tied to compute and I/O resources, meaning the number of nodes you provision must match the peak read and write QPS your workload demands, as each node provides a fixed amount of processing power and throughput. On the Google Professional Cloud Database Engineer exam, this concept tests your understanding that storage size is not a direct factor—Spanner automatically uses node resources for storage, so you can scale nodes for throughput without worrying about storage limits. A common trap is confusing storage requirements with throughput needs; remember that QPS drives node count, not data volume. Memory tip: “QPS drives nodes, storage just rides along.”
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
You are planning capacity for a Cloud Spanner instance. Which TWO factors directly affect the number of nodes required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Read throughput in queries per second (QPS)
Cloud Spanner node capacity is primarily determined by compute and I/O requirements, which are directly driven by read and write throughput (QPS). Each node provides a fixed amount of processing power and throughput; therefore, to handle a given QPS, you must provision enough nodes to meet the peak read and write demand. Storage size (Option E) is not a direct factor because Spanner automatically uses available node resources for storage, and you can add nodes for throughput without exceeding storage limits.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Number of users
Why it's wrong here
Number of users affects throughput but is indirect; throughput is the direct measure.
✓
Read throughput in queries per second (QPS)
Why this is correct
Read QPS directly determines CPU and node requirements.
Related concept
Read the scenario before looking for a memorised answer.
✗
Number of indexes
Why it's wrong here
Indexes affect write performance but are not a direct factor for node count; they are factored into throughput.
✓
Write throughput in queries per second (QPS)
Why this is correct
Write QPS directly determines CPU and memory needs for splitting and load.
Related concept
Read the scenario before looking for a memorised answer.
✗
Storage size in GB
Why it's wrong here
Storage size affects node count only when data exceeds per-node capacity, but throughput is the primary driver.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume storage size is a primary driver for node count, but Spanner decouples throughput and storage, so you must focus on QPS requirements first, especially in exam scenarios where throughput is the bottleneck.
Detailed technical explanation
How to think about this question
Under the hood, each Cloud Spanner node provides up to 10,000 read QPS and 2,000 write QPS (for 1 KB rows), and approximately 2 TB of SSD storage. However, storage is not a hard limit for node provisioning because Spanner can split data across nodes and you can add nodes for throughput without hitting storage limits. In real-world scenarios, a write-heavy workload with many indexes may require more nodes than storage suggests due to write amplification and the need for sufficient compute to handle commit timestamps and distributed transactions.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Read throughput in queries per second (QPS) — Cloud Spanner node capacity is primarily determined by compute and I/O requirements, which are directly driven by read and write throughput (QPS). Each node provides a fixed amount of processing power and throughput; therefore, to handle a given QPS, you must provision enough nodes to meet the peak read and write demand. Storage size (Option E) is not a direct factor because Spanner automatically uses available node resources for storage, and you can add nodes for throughput without exceeding storage limits.
What should I do if I get this PCDE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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