This PDE practice question tests your understanding of ensuring solution quality. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 company runs a real-time anomaly detection system on Google Cloud. Streaming data from IoT devices is ingested via Pub/Sub, processed by Dataflow (Apache Beam), and results are written to Bigtable for low-latency serving. Recently, the system has been experiencing increased latency and occasional data loss. The Dataflow pipeline shows high system lag and backlog in Pub/Sub. The Bigtable cluster has 3 nodes and is reporting high CPU utilization (over 90%). The team suspects the issue is with the pipeline configuration. They have already verified that there are no errors in the pipeline code and no network issues. Which action should they take to resolve the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Increase the number of Bigtable nodes to handle the write throughput.
The high CPU utilization on Bigtable (over 90%) indicates that the cluster is saturated and cannot keep up with the write throughput from Dataflow. This causes backpressure in the pipeline, leading to increased system lag and backlog in Pub/Sub, and eventually data loss when Pub/Sub messages expire. Increasing the number of Bigtable nodes directly addresses the bottleneck by distributing the write load and reducing CPU pressure, which allows the pipeline to drain the backlog and reduce 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.
✓
Increase the number of Bigtable nodes to handle the write throughput.
Why this is correct
High CPU utilization suggests Bigtable is overwhelmed; adding nodes increases capacity.
Related concept
Read the scenario before looking for a memorised answer.
✗
Change the Dataflow worker machine type to n2-standard-8.
Why it's wrong here
Faster workers would also increase write throughput, not solving the bottleneck.
✗
Decrease the batch size in the Dataflow pipeline to reduce latency.
Why it's wrong here
Smaller batches increase the number of write requests, putting more load on Bigtable.
✗
Increase the number of Dataflow workers to process messages faster.
Why it's wrong here
More workers would write more data to Bigtable, potentially worsening the bottleneck.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that scaling Dataflow workers or changing machine types always resolves pipeline latency, but the trap here is that the bottleneck is at the sink (Bigtable), so you must scale the sink first to relieve backpressure.
Detailed technical explanation
How to think about this question
Bigtable uses tablet servers to handle writes, and each node corresponds to one tablet server. When CPU exceeds 90%, write requests are queued and may be throttled, causing Dataflow to retry and build up a backlog. Bigtable's write throughput scales linearly with the number of nodes, but note that increasing nodes also increases the number of tablets and can improve load distribution. In real-world scenarios, a sudden spike in IoT data volume can overwhelm a small cluster, and simply scaling Dataflow workers without scaling Bigtable leads to increased write failures and data loss.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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.
Ensuring solution quality — This question tests Ensuring solution quality — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Increase the number of Bigtable nodes to handle the write throughput. — The high CPU utilization on Bigtable (over 90%) indicates that the cluster is saturated and cannot keep up with the write throughput from Dataflow. This causes backpressure in the pipeline, leading to increased system lag and backlog in Pub/Sub, and eventually data loss when Pub/Sub messages expire. Increasing the number of Bigtable nodes directly addresses the bottleneck by distributing the write load and reducing CPU pressure, which allows the pipeline to drain the backlog and reduce latency.
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.
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Question Discussion
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