The answer is to add a random prefix to the order ID primary key. This is correct because monotonically increasing keys, like sequential order IDs, create hot spots in Cloud Spanner by directing all new writes to a single split, overwhelming that node during high throughput events like flash sales. By adding a random prefix—such as a hash of the customer ID—you distribute writes across multiple splits, eliminating the hot spot and reducing latency spikes. On the Google Professional Cloud Architect exam, this scenario tests your understanding of Cloud Spanner’s split-based architecture and the common pitfall of sequential keys; a frequent trap is assuming indexing or caching alone will solve the issue. Remember the memory tip: “Prefix to spread, monotonic is dead”—always break up sequential keys with a hash or random prefix to ensure even write distribution.
Google PCA Practice Question: Analyze and optimize technical and business processes
This PCA practice question tests your understanding of analyze and optimize technical and business processes. 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.
An e-commerce platform uses Cloud Spanner for order processing. Recently, latency spikes have occurred during flash sales. The team suspects hot spots due to monotonically increasing order IDs. Which table design change would best solve this?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add a random prefix to the order ID primary key.
Monotonically increasing primary keys (like sequential order IDs) cause hot spots in Cloud Spanner because all writes are directed to a single split (tablet), overwhelming that node. Adding a random prefix (e.g., a hash of the customer ID) distributes writes across multiple splits, eliminating the hot spot and reducing latency spikes during high-throughput flash sales.
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.
✗
Remove the primary key and let Spanner auto-generate it.
Why it's wrong here
Spanner requires a primary key; auto-generation would still be monotonically increasing.
✗
Use interleaved tables to store orders under customers.
Why it's wrong here
Interleaving doesn't solve key hotspotting.
✓
Add a random prefix to the order ID primary key.
Why this is correct
Randomizing the first part of the key distributes writes across splits.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that secondary indexes or interleaved tables can fix write hot spots, when in reality only primary key distribution strategies (like hash prefixes) address the root cause of split-level contention.
Detailed technical explanation
How to think about this question
Cloud Spanner splits data by primary key range; each split is served by a separate node. Monotonically increasing keys cause all new writes to land on the last split, creating a single point of contention. By hashing the order ID or prepending a random prefix (e.g., a 4-byte hash), writes are uniformly distributed across all splits, leveraging Spanner's automatic load balancing. This technique is analogous to 'key sharding' in NoSQL systems and is recommended in Spanner's schema design best practices for high-write 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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PCA question in full detail.
Analyze and optimize technical and business processes — This question tests Analyze and optimize technical and business processes — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Add a random prefix to the order ID primary key. — Monotonically increasing primary keys (like sequential order IDs) cause hot spots in Cloud Spanner because all writes are directed to a single split (tablet), overwhelming that node. Adding a random prefix (e.g., a hash of the customer ID) distributes writes across multiple splits, eliminating the hot spot and reducing latency spikes during high-throughput flash sales.
What should I do if I get this PCA 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". 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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Question Discussion
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