PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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.
Your company runs a global application on Cloud Spanner. You notice that recent schema changes have caused a significant increase in latency for cross-node transactions. The previous schema used interleaved tables for parent-child relationships, but the new schema uses separate tables with foreign keys. What is the most likely cause of the increased latency?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The new schema uses foreign keys that require cross-node transactions.
The new schema uses separate tables with foreign keys instead of interleaved tables. In Cloud Spanner, interleaved tables guarantee that parent and child rows are co-located on the same split, allowing local joins without cross-node communication. Foreign keys between non-interleaved tables can reference rows stored on different splits, forcing distributed transactions that require two-phase commit across nodes, which significantly increases latency.
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.
✓
The new schema uses foreign keys that require cross-node transactions.
Why this is correct
Foreign keys between separate tables can lead to distributed transactions across nodes.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The new schema does not use commit timestamps for versioning.
Why it's wrong here
Commit timestamps are for MVCC, not directly related to cross-node latency.
✗
The new schema lacks secondary indexes on foreign key columns.
Why it's wrong here
Missing indexes can cause full table scans but not necessarily cross-node latency.
✗
The Spanner instance was not resized after the schema change.
Why it's wrong here
Resizing affects throughput but not the inherent latency of cross-node transactions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think foreign keys inherently cause performance issues due to constraint checking, but the real cause is the loss of data locality and resulting cross-split coordination in Spanner's distributed architecture.
Detailed technical explanation
How to think about this question
Cloud Spanner splits data into tablets based on primary key ranges; interleaved tables ensure child rows are stored in the same tablet as their parent, enabling single-round-trip reads. Without interleaving, a transaction that touches rows in different splits must use the Paxos-based two-phase commit protocol, which adds at least two additional round trips and increases latency by tens of milliseconds. In real-world scenarios, this latency becomes especially noticeable in globally distributed instances where splits are geographically separated.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The new schema uses foreign keys that require cross-node transactions. — The new schema uses separate tables with foreign keys instead of interleaved tables. In Cloud Spanner, interleaved tables guarantee that parent and child rows are co-located on the same split, allowing local joins without cross-node communication. Foreign keys between non-interleaved tables can reference rows stored on different splits, forcing distributed transactions that require two-phase commit across nodes, which significantly increases latency.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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