The correct answer is to use interleaved tables to co-locate related rows that are queried together. This schema design practice is essential for achieving global low-latency reads because Cloud Spanner physically stores parent and child rows on the same split, eliminating the need for cross-node communication during joins. When you interleave tables, related data resides in the same tablet, allowing Spanner to serve strongly consistent reads from a single regional replica without coordinating across distant nodes. On the Google Professional Cloud Database Engineer exam, this concept tests your understanding of how schema design directly impacts distributed database performance; a common trap is choosing denormalization or excessive indexing, which increase write overhead or storage costs without guaranteeing co-location. Remember the memory tip: “Interleave to retrieve, don’t index to fix”—if your queries always join a parent and child, interleaving is the performance shortcut that keeps reads fast across the globe.
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 company is designing a Cloud Spanner database for a global user base. They need to support strong consistency and low-latency reads across multiple regions. Which schema design practice is most important?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use interleaved tables to co-locate related rows that are queried together.
Option D is correct because interleaving tables that are frequently joined together into a parent-child hierarchy allows Spanner to co-locate the data, reducing cross-node communication and latency. Option A is wrong because using a single monolithic table would not scale. Option B is wrong because denormalization can increase write latency and complexity. Option C is wrong because indexing all columns leads to unnecessary overhead.
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.
✗
Denormalize data into wide tables to reduce the number of joins.
Why it's wrong here
Denormalization increases storage and write amplification, and may not be necessary with interleaving.
✓
Use interleaved tables to co-locate related rows that are queried together.
Why this is correct
Interleaving ensures parent and child rows are stored on the same split, reducing latency for joins.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single table with composite primary key to avoid joins.
Why it's wrong here
Single table approach does not leverage Spanner's distributed architecture and can cause hotspots.
✗
Create secondary indexes on every column to optimize read queries.
Why it's wrong here
Excessive indexes slow writes and are not always used; index design should be selective.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
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: Use interleaved tables to co-locate related rows that are queried together. — Option D is correct because interleaving tables that are frequently joined together into a parent-child hierarchy allows Spanner to co-locate the data, reducing cross-node communication and latency. Option A is wrong because using a single monolithic table would not scale. Option B is wrong because denormalization can increase write latency and complexity. Option C is wrong because indexing all columns leads to unnecessary overhead.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A startup is using Cloud Spanner for a global user base. They need to design a schema that minimizes interleaved table joins for common access patterns. Which schema design principle should they prioritize?
easy
A.Normalize all tables to reduce data redundancy.
B.Store data in separate databases per region.
C.Use secondary indexes on all foreign key columns.
✓ D.Use composite primary keys to colocate related data.
Why D: Interleaved tables in Spanner allow colocation of parent-child rows, reducing cross-node joins. Option A uses composite primary keys to colocate related data, which is the core principle of interleaving. Option B (normalization) increases joins. Option C (secondary indexes) helps but is not as fundamental. Option D (separate databases) increases complexity.
Last reviewed: Jun 24, 2026
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