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.
A Cloud Spanner database is experiencing slow query performance. Which approach should be taken to optimize read performance without compromising consistency?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add secondary indexes and use read-only transactions for read queries
Option C is correct because secondary indexes in Cloud Spanner allow efficient lookup of rows by non-key columns, avoiding full table scans. Read-only transactions provide a consistent snapshot of data without locking, which optimizes read performance while maintaining strong consistency.
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.
✗
Increase the number of Spanner nodes to boost throughput
Why it's wrong here
More nodes help with capacity but not with query optimization; poorly designed queries remain slow.
✗
Use interleaved tables to store related rows together
Why it's wrong here
Interleaved tables improve locality for hierarchical data but are not a general solution for slow queries.
✓
Add secondary indexes and use read-only transactions for read queries
Why this is correct
Secondary indexes avoid full table scans, and read-only transactions bypass lock overhead, improving read performance.
Related concept
Read the scenario before looking for a memorised answer.
✗
Migrate the data to Cloud Bigtable for better read performance
Why it's wrong here
Bigtable is optimized for key-value access, not for relational queries or complex transactions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that adding nodes always improves read performance, when in fact read optimization in Spanner relies on proper indexing and transaction type selection, not just scaling compute resources.
Detailed technical explanation
How to think about this question
Cloud Spanner uses a distributed Paxos-based replication protocol to maintain strong consistency across global nodes. Secondary indexes in Spanner are stored as separate tables that map indexed columns to base table keys, allowing point lookups or range scans without scanning the entire table. Read-only transactions leverage Spanner's TrueTime API to provide a globally consistent snapshot without acquiring locks, which is critical for high-read workloads.
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.
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: Add secondary indexes and use read-only transactions for read queries — Option C is correct because secondary indexes in Cloud Spanner allow efficient lookup of rows by non-key columns, avoiding full table scans. Read-only transactions provide a consistent snapshot of data without locking, which optimizes read performance while maintaining strong consistency.
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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