- A
Use a hashed prefix of the trade_id, e.g., [hash(trade_id)]#[trade_id]#[timestamp]
A hash prefix distributes writes across tablets by randomizing the start of the row key, reducing hot-spotting.
- B
Use a single row key of [timestamp]
Why wrong: Timestamp-only keys cause all writes to go to a single tablet at a time, worsening hot-spotting.
- C
Increase the number of Bigtable nodes to 20
Why wrong: Adding nodes can help throughput but does not fix hot-spotting caused by row key design.
- D
Change row key to [timestamp]#[trade_id]
Why wrong: Using timestamp first leads to sequential writes and hot-spotting on the current time range.
Question 120 of 1,000
PDE Storing the Data Practice Question
This PDE practice question tests your understanding of storing the data. 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 financial services company uses Cloud Bigtable to store trade data. They are experiencing hot-spotting on a single node, causing high latency. The row key format is [trade_id]#[timestamp]. Which row key design change would BEST distribute writes across tablets?
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
✓
Use a hashed prefix of the trade_id, e.g., [hash(trade_id)]#[trade_id]#[timestamp]
Option A is correct because adding a hashed prefix of the trade_id ensures that writes are evenly distributed across all Bigtable tablets. Bigtable partitions data by row key lexicographic order; without a hash, sequential trade IDs or timestamps cause all recent writes to land on a single tablet, creating a hotspot. The hash spreads the write load uniformly, regardless of the underlying key pattern.
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.
- ✓
Use a hashed prefix of the trade_id, e.g., [hash(trade_id)]#[trade_id]#[timestamp]
Why this is correct
A hash prefix distributes writes across tablets by randomizing the start of the row key, reducing hot-spotting.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a single row key of [timestamp]
Why it's wrong here
Timestamp-only keys cause all writes to go to a single tablet at a time, worsening hot-spotting.
- ✗
Increase the number of Bigtable nodes to 20
Why it's wrong here
Adding nodes can help throughput but does not fix hot-spotting caused by row key design.
- ✗
Change row key to [timestamp]#[trade_id]
Why it's wrong here
Using timestamp first leads to sequential writes and hot-spotting on the current time range.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that simply reversing the order of key components (e.g., putting the timestamp first) is sufficient to avoid hot-spotting, when in fact any monotonically increasing value at the start of the key will still cause a hotspot.
Detailed technical explanation
How to think about this question
Bigtable uses a distributed, sorted map where each tablet is a contiguous range of row keys. Without a hash prefix, sequential keys (e.g., timestamps) cause all new writes to target the last tablet, overwhelming it. A hash prefix like MD5 or CRC32 of the trade_id spreads writes across the entire key space, and Bigtable automatically splits tablets when they exceed ~256 MB, ensuring even load. In practice, you might also salt with a field like user_id to avoid collisions while maintaining query efficiency.
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.
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.
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FAQ
Questions learners often ask
What does this PDE question test?
Storing the Data — This question tests Storing the Data — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a hashed prefix of the trade_id, e.g., [hash(trade_id)]#[trade_id]#[timestamp] — Option A is correct because adding a hashed prefix of the trade_id ensures that writes are evenly distributed across all Bigtable tablets. Bigtable partitions data by row key lexicographic order; without a hash, sequential trade IDs or timestamps cause all recent writes to land on a single tablet, creating a hotspot. The hash spreads the write load uniformly, regardless of the underlying key pattern.
What should I do if I get this PDE 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.
About these practice questions
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Last reviewed: Jul 4, 2026
This PDE 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 PDE exam.
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