PCDOE Optimizing service performance Practice Question
This PCDOE practice question tests your understanding of optimizing service performance. 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.
Which TWO practices should be implemented to optimize query performance in Cloud Spanner?
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.
Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same split, reducing cross-node round trips and improving join performance. This design leverages Spanner's hierarchical storage model to minimize latency for queries that access related data together.
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.
✗
Split large tables into multiple smaller tables to distribute load.
Why it's wrong here
Manual splitting is not recommended; Spanner automatically splits data.
✗
Create as many indexes as possible on all columns.
Why it's wrong here
Excessive indexes slow down write operations.
✓
Use interleaved tables to co-locate related rows.
Why this is correct
Interleaving ensures parent and child rows are stored together, reducing cross-node reads.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use globally distributed interleaving across regions.
Why it's wrong here
Interleaving is for co-location within a region, not across regions.
✓
Define secondary indexes on columns used in WHERE clauses.
Why this is correct
Secondary indexes accelerate queries on non-key columns by avoiding full table scans.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that more indexes always improve query performance, but in Spanner, excessive indexes degrade write performance and storage efficiency, while interleaving and selective secondary indexes are the correct optimization strategies.
Detailed technical explanation
How to think about this question
Under the hood, Cloud Spanner uses a distributed Paxos-based storage engine where data is partitioned into splits by primary key range. Interleaved tables ensure child rows are stored physically adjacent to their parent row within the same split, enabling single-round-trip reads for hierarchical queries. A real-world scenario is an order management system where OrderItems are interleaved under Orders; querying all items for an order avoids distributed joins, reducing latency from tens of milliseconds to under 5 ms.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Optimizing service performance — This question tests Optimizing service performance — 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. — Option C is correct because interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same split, reducing cross-node round trips and improving join performance. This design leverages Spanner's hierarchical storage model to minimize latency for queries that access related data together.
What should I do if I get this PCDOE 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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Question Discussion
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