- A
Cloud Firestore in Datastore mode
Why wrong: Firestore provides single-digit millisecond latency, not microsecond. It also has more complexity for simple key-value cart storage.
- B
Cloud Bigtable
Bigtable delivers sub-millisecond (microsecond range) latency for key-value reads, scales horizontally, and persists data durably — ideal for the cart use case with a user ID row key.
- C
Cloud SQL (PostgreSQL)
Why wrong: Cloud SQL is a relational database with millisecond latency, not designed for microsecond high-throughput key-value access at horizontal scale.
- D
Cloud Memorystore (Redis)
Why wrong: Memorystore Redis provides microsecond latency but is an in-memory store; long-term 30-day persistence for all users' carts may be expensive and Memorystore is not designed for large-scale durable storage.
Quick Answer
The answer is Cloud Bigtable. This service is the correct choice because it provides low-latency persistent storage for shopping cart data, offering consistent sub-10ms reads that can approach microsecond latency for small key-value lookups under 1 KB, while its fully managed, horizontally scalable architecture handles high-frequency access during active sessions and retains data indefinitely beyond the required 30 days. On the Google Associate Cloud Engineer exam, this scenario tests your ability to distinguish Bigtable from Cloud SQL or Firestore; a common trap is choosing Firestore for its real-time features, but Bigtable’s superior read latency and throughput for operational workloads make it the fit here. Remember the memory tip: “Bigtable for big speed and small keys” — when you need microsecond reads on tiny entries with no expiration, Bigtable is the persistent, scalable answer.
Google ACE Planning and configuring a cloud solution Practice Question
This ACE practice question tests your understanding of planning and configuring a cloud solution. 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 solution for a retail application that needs to store customer shopping cart data. The cart data is accessed frequently during active sessions and must survive for at least 30 days even without activity. Each cart entry is small (< 1 KB) and identified by a user ID. The solution must support microsecond read latency and be horizontally scalable. Which GCP storage service best meets these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Clue:
"least"Why it matters: You want the option with minimum overhead, fewest steps, or lowest impact — not the most feature-rich or comprehensive answer.
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
Cloud Bigtable
Cloud Bigtable is correct because it is a fully managed, scalable NoSQL database designed for large analytical and operational workloads, offering consistent sub-10ms latency and horizontal scaling. For small (<1 KB) entries accessed with microsecond read latency, Bigtable's key-value model and high throughput make it ideal, and its data persists indefinitely (beyond 30 days) with no automatic expiration. It supports high-frequency access patterns typical of active shopping cart sessions.
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.
- ✗
Cloud Firestore in Datastore mode
Why it's wrong here
Firestore provides single-digit millisecond latency, not microsecond. It also has more complexity for simple key-value cart storage.
- ✓
Cloud Bigtable
Why this is correct
Bigtable delivers sub-millisecond (microsecond range) latency for key-value reads, scales horizontally, and persists data durably — ideal for the cart use case with a user ID row key.
Clue confirmation
The clue words "best", "least" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Cloud SQL (PostgreSQL)
Why it's wrong here
Cloud SQL is a relational database with millisecond latency, not designed for microsecond high-throughput key-value access at horizontal scale.
- ✗
Cloud Memorystore (Redis)
Why it's wrong here
Memorystore Redis provides microsecond latency but is an in-memory store; long-term 30-day persistence for all users' carts may be expensive and Memorystore is not designed for large-scale durable storage.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Cloud Memorystore (Redis) for its microsecond latency, overlooking that it is an in-memory cache with volatile data that does not guarantee persistence for 30 days without activity, whereas Bigtable provides durable, persistent storage with similar latency for small key-value entries.
Detailed technical explanation
How to think about this question
Bigtable uses a distributed, sorted key-value store built on Google's Colossus file system and SSTables, enabling automatic sharding and compaction for consistent low-latency access. Under the hood, it leverages Bigtable's tablet server architecture to distribute load across nodes, and row keys are lexicographically sorted to optimize range scans; for cart data, using a user ID as the row key ensures fast point lookups. A real-world scenario is an e-commerce platform handling millions of concurrent sessions where cart data must persist for abandoned carts; Bigtable's lack of automatic TTL (unless explicitly set with garbage collection) ensures data survives indefinitely, meeting the 30-day requirement without extra configuration.
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.
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FAQ
Questions learners often ask
What does this ACE question test?
Planning and configuring a cloud solution — This question tests Planning and configuring a cloud solution — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Cloud Bigtable — Cloud Bigtable is correct because it is a fully managed, scalable NoSQL database designed for large analytical and operational workloads, offering consistent sub-10ms latency and horizontal scaling. For small (<1 KB) entries accessed with microsecond read latency, Bigtable's key-value model and high throughput make it ideal, and its data persists indefinitely (beyond 30 days) with no automatic expiration. It supports high-frequency access patterns typical of active shopping cart sessions.
What should I do if I get this ACE 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: "best", "least". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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