- A
Export data periodically to BigQuery and run queries there.
Why wrong: This is possible but adds data staleness and operational overhead; not a pure schema design technique.
- B
Create multiple secondary indexes on frequently scanned columns.
Why wrong: Secondary indexes are optimized for point lookups, not large scans; they can also introduce write overhead.
- C
Design the primary key so that analytical queries scan a small number of tablets by using interleaved tables.
Interleaving related rows keeps them co-located, allowing efficient scans on parent-child relationships without distributed reads.
- D
Use a read replica instance to offload analytical queries.
Why wrong: Cloud Spanner does not have read replicas; it uses a single strong-consistent architecture.
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 financial services company uses Cloud Spanner for transaction processing. They need to run analytical queries that scan large portions of the database without impacting OLTP performance. What schema design technique should they use?
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
Design the primary key so that analytical queries scan a small number of tablets by using interleaved tables.
Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same tablet (split). This ensures that analytical queries scanning a large portion of the database can be served by a small number of tablets, minimizing cross-tablet reads and reducing contention with OLTP traffic. By designing the primary key to leverage interleaving, you keep analytical scans localized and avoid the performance penalty of scattering reads across many tablets.
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.
- ✗
Export data periodically to BigQuery and run queries there.
Why it's wrong here
This is possible but adds data staleness and operational overhead; not a pure schema design technique.
- ✗
Create multiple secondary indexes on frequently scanned columns.
Why it's wrong here
Secondary indexes are optimized for point lookups, not large scans; they can also introduce write overhead.
- ✓
Design the primary key so that analytical queries scan a small number of tablets by using interleaved tables.
Why this is correct
Interleaving related rows keeps them co-located, allowing efficient scans on parent-child relationships without distributed reads.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a read replica instance to offload analytical queries.
Why it's wrong here
Cloud Spanner does not have read replicas; it uses a single strong-consistent architecture.
Common exam traps
Common exam trap: answer the scenario, not the keyword
A common misconception is that read replicas or secondary indexes are the primary way to isolate analytical workloads, but in Cloud Spanner the correct schema-level isolation technique is interleaved tables to minimize tablet scans and avoid cross-split contention.
Detailed technical explanation
How to think about this question
Cloud Spanner's interleaved tables use a parent-child relationship where child rows are stored physically adjacent to their parent row within the same split (tablet). This design allows range scans on the parent key to efficiently retrieve all related child rows without cross-tablet RPCs. In practice, for a financial services company running daily reconciliation queries that scan all transactions for a given account, interleaving the Transactions table under the Accounts table ensures the scan touches only the tablets holding that account's data, leaving other tablets unaffected for OLTP.
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
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FAQ
Questions learners often ask
What does this PCDE question test?
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: Design the primary key so that analytical queries scan a small number of tablets by using interleaved tables. — Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same tablet (split). This ensures that analytical queries scanning a large portion of the database can be served by a small number of tablets, minimizing cross-tablet reads and reducing contention with OLTP traffic. By designing the primary key to leverage interleaving, you keep analytical scans localized and avoid the performance penalty of scattering reads across many tablets.
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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Last reviewed: Jul 4, 2026
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