- A
Interleave the Posts table under the Users table, with user_id as parent key and post_timestamp as the child ordering key.
Interleaving ensures all posts of a user are stored together, enabling fast retrieval.
- B
Use a secondary index on user_id in the Posts table.
Why wrong: Index lookups involve an extra hop and may not be co-located, increasing latency.
- C
Create a single table with user_id and post_timestamp as a composite primary key.
Why wrong: Without interleaving, rows may be distributed across nodes, causing higher latency.
- D
Store posts in a separate Cloud Bigtable table and use the user_id as part of the row key.
Why wrong: This adds cross-service latency and complexity.
Question 377 of 1,000
PCDOE Design and Plan Database Solutions Practice Question
This PCDOE practice question tests your understanding of design and plan database solutions. 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.
You are designing a Spanner schema for a global social media application that stores user posts. Each user can have millions of posts. The most common query is 'get the most recent 10 posts for a user'. Which table interleaving design minimizes latency?
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
✓
Interleave the Posts table under the Users table, with user_id as parent key and post_timestamp as the child ordering key.
Option A is correct because interleaving the Posts table under the Users table in Spanner ensures that all posts for a given user are stored in the same split, co-located on the same tablet server. This allows the query for the most recent 10 posts to be served with a single, local range scan on the interleaved child table, using post_timestamp as the descending ordering key, minimizing cross-node communication and 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.
- ✓
Interleave the Posts table under the Users table, with user_id as parent key and post_timestamp as the child ordering key.
Why this is correct
Interleaving ensures all posts of a user are stored together, enabling fast retrieval.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a secondary index on user_id in the Posts table.
Why it's wrong here
Index lookups involve an extra hop and may not be co-located, increasing latency.
- ✗
Create a single table with user_id and post_timestamp as a composite primary key.
Why it's wrong here
Without interleaving, rows may be distributed across nodes, causing higher latency.
- ✗
Store posts in a separate Cloud Bigtable table and use the user_id as part of the row key.
Why it's wrong here
This adds cross-service latency and complexity.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that a secondary index or composite primary key alone provides the same performance as interleaving, but they fail to guarantee physical co-location, which is critical for minimizing latency in globally distributed databases.
Detailed technical explanation
How to think about this question
Spanner interleaving physically co-locates parent and child rows in the same tablet, enabling atomic row operations and efficient range scans without distributed transactions. The child table's interleaved ordering key (post_timestamp) allows a descending LIMIT query to read only the required number of rows from the local storage, leveraging Spanner's lock-free read paths. In a real-world scenario with millions of posts per user, this design avoids the 'hotspotting' issue that can occur with monotonically increasing keys in a non-interleaved table.
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.
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FAQ
Questions learners often ask
What does this PCDOE question test?
Design and Plan Database Solutions — This question tests Design and Plan Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Interleave the Posts table under the Users table, with user_id as parent key and post_timestamp as the child ordering key. — Option A is correct because interleaving the Posts table under the Users table in Spanner ensures that all posts for a given user are stored in the same split, co-located on the same tablet server. This allows the query for the most recent 10 posts to be served with a single, local range scan on the interleaved child table, using post_timestamp as the descending ordering key, minimizing cross-node communication and latency.
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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Last reviewed: Jul 4, 2026
This PCDOE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCDOE exam.
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