- A
Interleaved tables cannot be joined
Why wrong: Interleaved tables are designed to be joined on the interleave key.
- B
The join will be fast because interleaving stores child rows with the parent row in the same split
Interleaving ensures co-location, making joins on the parent key efficient.
- C
The join will be slow because interleaving increases split overhead
Why wrong: Interleaving reduces split overhead and improves locality.
- D
The join is only fast if you use a global secondary index
Why wrong: Global secondary indexes are not needed; interleaving already provides co-location.
Question 356 of 999
Design Scalable and Highly Available Cloud Database Solutions →mediumMultiple ChoiceObjective-mapped
PCD Practice Question: Design Scalable and Highly Available Cloud Database Solutions
This PCD practice question tests your understanding of design scalable and highly available cloud database solutions. 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 manage a global ecommerce platform using Cloud Spanner. You need to support a query that joins two tables on a foreign key relationship. The tables are parent and child in an interleaved table hierarchy. Which statement about performance is TRUE?
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
✓
The join will be fast because interleaving stores child rows with the parent row in the same split
Option B is correct because Cloud Spanner interleaved tables physically co-locate child rows with their parent row within the same split (and often the same tablet). This means a join on the interleaved foreign key can be executed with minimal cross-node communication, as the data needed for the join is stored together, resulting in very fast query performance.
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.
- ✗
Interleaved tables cannot be joined
Why it's wrong here
Interleaved tables are designed to be joined on the interleave key.
- ✓
The join will be fast because interleaving stores child rows with the parent row in the same split
Why this is correct
Interleaving ensures co-location, making joins on the parent key efficient.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The join will be slow because interleaving increases split overhead
Why it's wrong here
Interleaving reduces split overhead and improves locality.
- ✗
The join is only fast if you use a global secondary index
Why it's wrong here
Global secondary indexes are not needed; interleaving already provides co-location.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think interleaving is only for hierarchical data storage and not for query performance, or they may confuse interleaving with traditional foreign key relationships that require distributed joins.
Detailed technical explanation
How to think about this question
Under the hood, Cloud Spanner uses a distributed storage layer where splits are the unit of data placement and replication. When you define an interleaved table, the child table's rows are stored in the same split as the parent row, ordered by the parent key. This means a join on the interleaved key can be executed as a local index scan within the same split, avoiding the need for a distributed query across multiple nodes. In real-world scenarios, this is critical for high-throughput transactional workloads, such as an ecommerce platform's order and order_items tables, where joining on the order ID must be fast and consistent.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCD question test?
Design Scalable and Highly Available Cloud Database Solutions — This question tests Design Scalable and Highly Available Cloud Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The join will be fast because interleaving stores child rows with the parent row in the same split — Option B is correct because Cloud Spanner interleaved tables physically co-locate child rows with their parent row within the same split (and often the same tablet). This means a join on the interleaved foreign key can be executed with minimal cross-node communication, as the data needed for the join is stored together, resulting in very fast query performance.
What should I do if I get this PCD 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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Last reviewed: Jul 4, 2026
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