PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Exhibit
Refer to the exhibit.
gcloud spanner instances describe test-instance
-- output:
config: nam3
nodeCount: 2
processingUnits: 2000
state: READY
-- Schema:
CREATE TABLE Events (
EventId INT64 NOT NULL,
EventType STRING(50) NOT NULL,
EventData BYTES(MAX) NOT NULL,
CreatedAt TIMESTAMP NOT NULL OPTIONS (allow_commit_timestamp=true)
) PRIMARY KEY (EventId);
Refer to the exhibit. The team notices high write latency on the Events table. They are inserting 1,000 events per second. The EventId is generated by a sequence. What is the most likely issue?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The sequential primary key creates a hotspot on a single split.
Option B is correct because using a sequential integer as primary key causes hotspotting on the last split, as all new writes go to the same tablet. Option A is wrong because 2000 processing units (equivalent to 2 nodes) can handle 1k writes/s if distributed. Option C is wrong because BYTES(MAX) may increase size but not the primary cause of latency. Option D is wrong because commit timestamp option does not cause hotspotting.
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.
✓
The sequential primary key creates a hotspot on a single split.
Why this is correct
Sequential keys cause all writes to hit the same split, leading to contention and latency.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The allow_commit_timestamp option on CreatedAt column adds overhead.
Why it's wrong here
Commit timestamp option is efficient and not a cause of hotspotting.
✗
The BYTES(MAX) data type causes excessive writing.
Why it's wrong here
Data size affects throughput but not specifically the hotspot issue.
✗
The node count is insufficient for the write throughput.
Why it's wrong here
2 nodes can handle 1k writes/s if writes are distributed; the issue is distribution.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Design and implement database schemas — This question tests Design and implement database schemas — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The sequential primary key creates a hotspot on a single split. — Option B is correct because using a sequential integer as primary key causes hotspotting on the last split, as all new writes go to the same tablet. Option A is wrong because 2000 processing units (equivalent to 2 nodes) can handle 1k writes/s if distributed. Option C is wrong because BYTES(MAX) may increase size but not the primary cause of latency. Option D is wrong because commit timestamp option does not cause hotspotting.
What should I do if I get this PCDE question wrong?
Identify which PCDE exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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