PDE Practice Question: Building and operationalizing data processing systems
This PDE practice question tests your understanding of building and operationalizing data processing systems. 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.
Your company uses Cloud Dataflow to process streaming data from Pub/Sub. The pipeline occasionally fails with a 'worker terminated unexpectedly' error. What is the most likely cause of this error?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Insufficient memory per worker causing OOM errors
The 'worker terminated unexpectedly' error in Cloud Dataflow typically indicates that a worker process ran out of memory (OOM) and was killed by the operating system. This occurs when the pipeline's memory requirements exceed the configured worker machine type's memory capacity, often due to large windowing accumulations, skewed data, or inefficient state handling.
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.
✓
Insufficient memory per worker causing OOM errors
Why this is correct
OOM errors cause workers to terminate unexpectedly.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Incorrect VPC firewall rules blocking internal communication
Why it's wrong here
Firewall rules affect connectivity but not worker termination.
✗
Staging location bucket lacks write permissions
Why it's wrong here
Permissions issues cause access errors, not termination.
✗
Pub/Sub subscription throughput quota exceeded
Why it's wrong here
Quota exceeded causes throttling, not worker termination.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between infrastructure-level errors (like OOM) and configuration or permission errors, so candidates may incorrectly attribute the generic 'worker terminated' message to network or IAM issues rather than resource exhaustion.
Detailed technical explanation
How to think about this question
Under the hood, Dataflow workers run as containers on Compute Engine VMs. When a worker exceeds its memory limit, the Linux Out-Of-Memory (OOM) killer terminates the Java process, causing the worker to report as terminated. This is especially common with stateful transforms (e.g., GroupByKey, Combine) that accumulate data in memory over large windows. Monitoring worker memory utilization via Stackdriver and choosing a machine type with more memory (e.g., n1-highmem) or enabling autoscaling can mitigate this.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Building and operationalizing data processing systems — This question tests Building and operationalizing data processing systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Insufficient memory per worker causing OOM errors — The 'worker terminated unexpectedly' error in Cloud Dataflow typically indicates that a worker process ran out of memory (OOM) and was killed by the operating system. This occurs when the pipeline's memory requirements exceed the configured worker machine type's memory capacity, often due to large windowing accumulations, skewed data, or inefficient state handling.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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