Quick Answer
The correct schema design for achieving global consistency with low write latency in Cloud Spanner is to use parent-child table relationships with interleaved tables. This works because interleaved tables physically co-locate parent and child rows on the same split, ensuring that strongly consistent reads and writes for related data occur within a single node rather than requiring costly cross-node coordination. By storing related rows together, interleaving eliminates the distributed transaction overhead that would otherwise increase write latency when operations span parent-child relationships. On the Google Professional Cloud Developer exam, this concept tests your understanding of how schema design directly impacts performance trade-offs in globally distributed databases; a common trap is choosing secondary indexes or denormalization, which can increase write latency due to cross-split coordination. Remember the mnemonic “Interleave to relieve” — interleaving relieves the latency burden by keeping family data physically close.
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native applications. 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 uses Cloud Spanner for a financial application. They need to ensure strong global consistency but also minimize latency for writes. What schema design should they use?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Use secondary indexes
Why wrong: Secondary indexes increase write overhead.
Use commit timestamps
Why wrong: Commit timestamps are for tracking versions, not reducing latency.
Use parent-child table relationships with interleaved tables
Interleaving allows co-location of related rows, reducing write latency.
Use a single table with interleaved indexes
Why wrong: There is no such concept; interleaved indexes are for parent-child tables.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use parent-child table relationships with interleaved tables
Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same split, reducing cross-node coordination for strongly consistent reads and writes. This minimizes write latency by ensuring that related data is stored together, avoiding distributed transaction overhead for operations that span parent-child relationships.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Use secondary indexes
Why it's wrong here
Secondary indexes increase write overhead.
Use commit timestamps
Why it's wrong here
Commit timestamps are for tracking versions, not reducing latency.
Use parent-child table relationships with interleaved tables
Why this is correct
Interleaving allows co-location of related rows, reducing write latency.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Use a single table with interleaved indexes
Why it's wrong here
There is no such concept; interleaved indexes are for parent-child tables.
Common exam traps
The trap here is that candidates confuse interleaved tables with secondary indexes or commit timestamps, thinking those features directly reduce write latency, when in fact only physical co-location through interleaved tables achieves that goal in a globally consistent system.
Detailed technical explanation
Interleaved tables in Cloud Spanner use a parent-child relationship where child rows are stored physically adjacent to their parent row within the same split (a Paxos group). This co-location allows strongly consistent reads and writes to be handled by a single leader, avoiding two-phase commit across splits. In a real-world financial application, this means that transactions involving an account (parent) and its transactions (child) can be committed with low latency, even under global consistency requirements.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
The correct answer is: Use parent-child table relationships with interleaved tables — Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same split, reducing cross-node coordination for strongly consistent reads and writes. This minimizes write latency by ensuring that related data is stored together, avoiding distributed transaction overhead for operations that span parent-child relationships.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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