The answer is to configure fixed windows with .withAllowedLateness(Duration.standardMinutes(10)). This is correct because the `withAllowedLateness` method explicitly instructs the Dataflow pipeline to retain the window state and trigger late-arriving events for a specified duration after the watermark has passed the window’s end, ensuring that any event arriving within that 10-minute grace period is still included in the correct window and written to BigQuery. On the Google Professional Data Engineer exam, this scenario tests your understanding of how Dataflow handles out-of-order data in streaming pipelines, often appearing as a distractor where candidates mistakenly choose `withAllowedLateness` on global windows or confuse it with trigger settings. A common trap is thinking that simply increasing the window size or using `withTimestampAttribute` alone solves late data, but only `withAllowedLateness` directly extends the window’s lifetime for late arrivals. Memory tip: think of “lateness” as a “late pass” for events—set the duration to match your tolerance, and the watermark will wait before closing the window.
PDE Designing data processing systems Practice Question
This PDE practice question tests your understanding of designing data processing systems. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 team runs a Dataflow streaming pipeline that reads from Pub/Sub, windows events by processing time, and writes to BigQuery. Some late-arriving events are being dropped. The requirement is to include all events that arrive within 10 minutes of the watermark. Which pipeline configuration should be used?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use fixed windows with .withAllowedLateness(Duration.standardMinutes(10))
Option B is correct because `withAllowedLateness(Duration.standardMinutes(10))` on a fixed window allows late-arriving events to be included up to 10 minutes after the watermark passes the window's end. This directly meets the requirement to retain events arriving within 10 minutes of the watermark, while still using processing-time windows as specified.
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 sliding windows with no allowed lateness
Why it's wrong here
No allowed lateness drops all late data.
✓
Use fixed windows with .withAllowedLateness(Duration.standardMinutes(10))
Why this is correct
Allows late data up to 10 minutes after watermark.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use fixed windows with withAllowedLateness(Duration.standardSeconds(10))
Why it's wrong here
10 seconds is insufficient; need 10 minutes.
✗
Switch from processing time to event time and use default triggers
Why it's wrong here
Event time alone does not set allowed lateness; defaults are zero.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between processing time and event time, and the exact value of allowed lateness, tricking candidates into choosing a shorter duration or the wrong window type.
Detailed technical explanation
How to think about this question
In Apache Beam (the SDK underlying Dataflow), `withAllowedLateness` extends the window's life beyond the watermark, allowing late data to trigger additional pane emissions. The watermark is a heuristic that estimates event completeness; setting allowed lateness to 10 minutes means the window remains open for late data until the watermark advances 10 minutes past the window's end, after which late data is discarded. This is critical for streaming pipelines where network delays or out-of-order arrivals are common.
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.
Designing data processing systems — This question tests Designing data processing systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use fixed windows with .withAllowedLateness(Duration.standardMinutes(10)) — Option B is correct because `withAllowedLateness(Duration.standardMinutes(10))` on a fixed window allows late-arriving events to be included up to 10 minutes after the watermark passes the window's end. This directly meets the requirement to retain events arriving within 10 minutes of the watermark, while still using processing-time windows as specified.
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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