The answer is to create indexes on foreign key columns. This improves write performance because when a row is inserted, updated, or deleted in a parent table, the database must check all child tables for referential integrity; without an index on the foreign key column, PostgreSQL performs a full table scan on the child table for each such operation, dramatically slowing writes. On the Google Professional Cloud Database Engineer exam, this concept tests your understanding of how schema design directly impacts OLTP throughput—a common trap is assuming that more constraints or larger storage will solve performance issues, when in reality the missing index is the bottleneck. Remember the mnemonic: “FK needs a key” to recall that every foreign key column should have an index to avoid costly sequential scans and keep write-heavy workloads fast.
PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. 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.
A Cloud SQL for PostgreSQL instance is used for an OLTP application. The database schema has many foreign key constraints. Which action improves write performance?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create indexes on foreign key columns.
Option A is correct because creating indexes on foreign key columns avoids full table scans during referential integrity checks. Option B is wrong as more triggers slow writes. Option C is wrong because dropping constraints risks data integrity. Option D is wrong because increasing disk size does not directly address the performance bottleneck.
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.
✓
Create indexes on foreign key columns.
Why this is correct
Indexes on foreign key columns speed up lookups during INSERT/UPDATE/DELETE operations.
Related concept
Read the scenario before looking for a memorised answer.
✗
Drop all foreign key constraints.
Why it's wrong here
Dropping constraints compromises data integrity and is not a recommended solution.
✗
Add more triggers to enforce integrity.
Why it's wrong here
Triggers add overhead and do not help with foreign key performance.
✗
Increase the instance storage size.
Why it's wrong here
Storage size does not directly affect the performance of foreign key validation.
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 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 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: Create indexes on foreign key columns. — Option A is correct because creating indexes on foreign key columns avoids full table scans during referential integrity checks. Option B is wrong as more triggers slow writes. Option C is wrong because dropping constraints risks data integrity. Option D is wrong because increasing disk size does not directly address the performance bottleneck.
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.
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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