The answer is that the Pub/Sub subscription’s acknowledgement deadline is too short for the processing time. This is correct because when a Dataflow pipeline reads from Pub/Sub, each message must be acknowledged within the subscription’s configured deadline; if processing takes longer, the deadline expires and Pub/Sub redelivers the message, causing duplicate work and eventual ‘deadline exceeded’ errors. On the Google Professional Data Engineer exam, this scenario tests your understanding of streaming pipeline backpressure and Pub/Sub’s flow control mechanics—a common trap is to misdiagnose the issue as a network timeout or insufficient worker resources, when the root cause is simply that the default 10-second ack deadline is too tight for your transformation logic. To remember this, think of the “10-second rule”: if your pipeline’s per-message processing time exceeds ten seconds, you must increase the acknowledgement deadline or risk redelivery chaos.
PDE Ensuring solution quality Practice Question
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 data pipeline ingests streaming data from Pub/Sub into BigQuery via Dataflow. Recently, the pipeline has been failing with 'deadline exceeded' errors. What is the most likely cause?
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
✓
The Pub/Sub subscription's acknowledgement deadline is too short for the processing time.
Option D is correct because 'deadline exceeded' errors in a Dataflow pipeline reading from Pub/Sub indicate that the subscriber is taking longer to process messages than the acknowledgement deadline allows. When the deadline expires, Pub/Sub redelivers the message, causing duplicate processing and eventual pipeline failure. This is a common issue when processing time exceeds the default 10-second acknowledgement deadline.
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.
✗
The BigQuery streaming quota is exceeded.
Why it's wrong here
Quota exceeded errors would be 'quota exceeded', not 'deadline exceeded'.
✗
Dataflow workers are underutilized due to batch size settings.
Why it's wrong here
Underutilization would not cause deadline exceeded errors; it might cause slow processing.
✗
Dataflow autoscaling is disabled.
Why it's wrong here
Autoscaling being disabled might cause performance issues but not specifically deadline exceeded errors.
✓
The Pub/Sub subscription's acknowledgement deadline is too short for the processing time.
Why this is correct
A short acknowledgment deadline causes messages to be redelivered, leading to repeated processing attempts and eventual deadline exceeded errors.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between resource quota errors (like BigQuery streaming quota) and Pub/Sub-specific timeout errors, trapping candidates who confuse 'deadline exceeded' with general quota exhaustion.
Detailed technical explanation
How to think about this question
Pub/Sub uses a configurable acknowledgement deadline (default 10 seconds, max 600 seconds) during which the subscriber must acknowledge the message. If processing takes longer, the message becomes eligible for redelivery, and repeated failures can cause the pipeline to stall. Dataflow's streaming engine uses checkpointing and exactly-once semantics, but if the acknowledgement deadline is too short, messages are redelivered before processing completes, leading to 'deadline exceeded' errors in the worker logs.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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: The Pub/Sub subscription's acknowledgement deadline is too short for the processing time. — Option D is correct because 'deadline exceeded' errors in a Dataflow pipeline reading from Pub/Sub indicate that the subscriber is taking longer to process messages than the acknowledgement deadline allows. When the deadline expires, Pub/Sub redelivers the message, causing duplicate processing and eventual pipeline failure. This is a common issue when processing time exceeds the default 10-second acknowledgement deadline.
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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