PCDE Design and implement database schemas Practice Question
This PCDE practice question tests your understanding of design and implement database schemas. 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 global gaming company uses Cloud Spanner for player profiles and game state. The schema includes a table 'PlayerStats' with a primary key (PlayerId, GameId, Timestamp). The table stores millions of rows per player. The application frequently runs a query to fetch the most recent stats for a given player across all games, using ORDER BY Timestamp DESC LIMIT 10. This query is slow, taking several seconds. The team adds a secondary index on (PlayerId, Timestamp) but still sees high CPU usage and latency. They need to redesign the schema to optimize this query without changing the application logic significantly. What should they do?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Change the primary key to (PlayerId, Timestamp, GameId) and drop the secondary index.
Option A is correct. Reordering the primary key to (PlayerId, Timestamp, GameId) allows Spanner to efficiently perform a range scan for a given PlayerId, sorted by Timestamp, without needing a secondary index. This eliminates the need for the index and reduces CPU. Option B is not a schema change. Option C is a different database, not a schema redesign. Option D is not supported in Spanner natively.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Migrate the PlayerStats table to Cloud Bigtable for better time-series performance.
Why it's wrong here
Migrating databases is a major architectural change, not a schema redesign.
✓
Change the primary key to (PlayerId, Timestamp, GameId) and drop the secondary index.
Why this is correct
This allows efficient range scans for a player’s stats ordered by time.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
Create a stored procedure that aggregates data per player and caches results.
Why it's wrong here
This is an application-level change, not a schema design change.
✗
Add a materialized view that pre-computes the latest stats per player.
Why it's wrong here
Cloud Spanner does not support materialized views natively.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.
Design and implement database schemas — This question tests Design and implement database schemas — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Change the primary key to (PlayerId, Timestamp, GameId) and drop the secondary index. — Option A is correct. Reordering the primary key to (PlayerId, Timestamp, GameId) allows Spanner to efficiently perform a range scan for a given PlayerId, sorted by Timestamp, without needing a secondary index. This eliminates the need for the index and reduces CPU. Option B is not a schema change. Option C is a different database, not a schema redesign. Option D is not supported in Spanner natively.
What should I do if I get this PCDE question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related PCDE NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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