- A
The Cloud Storage bucket notification is not sending messages to the correct Pub/Sub topic, or the subscription's ack deadline is too short.
C is correct because misconfiguration of the notification or subscription can cause message loss.
- B
The DAG's start_date is set in the past and catchup is set to False, so DAG runs are only triggered on schedule.
Why wrong: E is wrong because the DAG is sensor-triggered, not schedule-triggered.
- C
The total number of DAGs in the environment exceeds the maximum limit of 100, causing DAG processing to stop.
Why wrong: A is wrong because the default limit is 500 DAGs, and even if exceeded, Composer does not stop processing.
- D
The DAG's schedule interval is set too frequently, causing the executor queue to be full and new runs are skipped.
B is correct because if the DAG execution takes longer than the interval, subsequent runs may be queued and skipped.
- E
The Cloud Composer environment is using a pull subscription instead of a push subscription for the Pub/Sub sensor.
Why wrong: D is wrong because Cloud Composer's Pub/Sub sensors use pull subscriptions.
Quick Answer
The answer is a misconfigured Pub/Sub topic subscription and an overly short acknowledgment deadline. When a Cloud Composer DAG is not starting from a Pub/Sub trigger, the most likely cause is that the Cloud Storage bucket notification is sending messages to the wrong Pub/Sub topic, so the DAG’s Pub/Sub sensor never receives the trigger. Alternatively, if the subscription’s ack deadline is too short, the message may be acknowledged before the sensor processes it, causing the trigger to be lost entirely. On the Google Professional Data Engineer exam, this scenario tests your understanding of how Cloud Composer’s sensor-based triggers interact with Pub/Sub’s delivery semantics—a common trap is assuming the DAG schedule is at fault when the issue is actually upstream in the messaging pipeline. Remember the mnemonic “Topic and Time”: verify the topic is correct and the ack deadline is long enough for the sensor to process the message.
PDE Practice Question: Building and operationalizing data processing systems
This PDE practice question tests your understanding of building and operationalizing 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 company uses Cloud Composer to orchestrate data pipelines. They have a DAG that runs hourly and processes files from Cloud Storage. The DAG is triggered by a Pub/Sub message sent from a Cloud Storage bucket notification. Recently, some DAG runs are not starting even though the Pub/Sub messages are published. Which two likely causes should the team investigate? (Choose TWO.)
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
The Cloud Storage bucket notification is not sending messages to the correct Pub/Sub topic, or the subscription's ack deadline is too short.
Option A is correct because if the Cloud Storage bucket notification is misconfigured to send messages to the wrong Pub/Sub topic, the Pub/Sub sensor in the DAG will never receive the trigger message, causing DAG runs to not start. Additionally, if the subscription's ack deadline is too short, the message may be acknowledged before the sensor processes it, leading to message loss and missed triggers. Both issues directly prevent the DAG from being triggered by Pub/Sub messages.
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 Cloud Storage bucket notification is not sending messages to the correct Pub/Sub topic, or the subscription's ack deadline is too short.
Why this is correct
C is correct because misconfiguration of the notification or subscription can cause message loss.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The DAG's start_date is set in the past and catchup is set to False, so DAG runs are only triggered on schedule.
Why it's wrong here
E is wrong because the DAG is sensor-triggered, not schedule-triggered.
- ✗
The total number of DAGs in the environment exceeds the maximum limit of 100, causing DAG processing to stop.
Why it's wrong here
A is wrong because the default limit is 500 DAGs, and even if exceeded, Composer does not stop processing.
- ✓
The DAG's schedule interval is set too frequently, causing the executor queue to be full and new runs are skipped.
Why this is correct
B is correct because if the DAG execution takes longer than the interval, subsequent runs may be queued and skipped.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The Cloud Composer environment is using a pull subscription instead of a push subscription for the Pub/Sub sensor.
Why it's wrong here
D is wrong because Cloud Composer's Pub/Sub sensors use pull subscriptions.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that a push subscription is required for Pub/Sub sensors in Cloud Composer, when in fact the sensor uses a pull subscription and the ack deadline is the critical parameter to manage.
Detailed technical explanation
How to think about this question
Cloud Composer uses a Pub/Sub sensor (e.g., PubSubPullSensor) that relies on a pull subscription to retrieve messages. The ack deadline is critical: if the sensor does not acknowledge the message within the deadline (default 10 seconds), the message becomes available for redelivery, but if the sensor has already processed it, the message is lost. Bucket notifications are configured via the Cloud Storage API, which sends notifications to a Pub/Sub topic; misconfiguration here (e.g., wrong topic ID or project) is a common root cause for silent failures.
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 — study guide chapter
Learn the concepts, then practise the questions
- →
Building and operationalizing data processing systems practice questions
Targeted practice on this topic area only
- →
All PDE questions
499 questions across all exam domains
- →
Google Professional Data Engineer study guide
Full concept coverage aligned to exam objectives
- →
PDE practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related PDE practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Designing data processing systems practice questions
Practise PDE questions linked to Designing data processing systems.
Building and operationalizing data processing systems practice questions
Practise PDE questions linked to Building and operationalizing data processing systems.
Operationalizing machine learning models practice questions
Practise PDE questions linked to Operationalizing machine learning models.
Ensuring solution quality practice questions
Practise PDE questions linked to Ensuring solution quality.
PDE fundamentals practice questions
Practise PDE questions linked to PDE fundamentals.
PDE scenario practice questions
Practise PDE questions linked to PDE scenario.
PDE troubleshooting practice questions
Practise PDE questions linked to PDE troubleshooting.
Practice this exam
Start a free PDE practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this PDE question test?
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: The Cloud Storage bucket notification is not sending messages to the correct Pub/Sub topic, or the subscription's ack deadline is too short. — Option A is correct because if the Cloud Storage bucket notification is misconfigured to send messages to the wrong Pub/Sub topic, the Pub/Sub sensor in the DAG will never receive the trigger message, causing DAG runs to not start. Additionally, if the subscription's ack deadline is too short, the message may be acknowledged before the sensor processes it, leading to message loss and missed triggers. Both issues directly prevent the DAG from being triggered by Pub/Sub messages.
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
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More PDE practice questions
- A company wants to process large CSV files stored in Cloud Storage and load them into BigQuery. The files are generated…
- A company runs a Dataflow streaming pipeline that reads from Cloud Pub/Sub and writes to BigQuery. The pipeline uses a s…
- Your company uses Vertex AI Pipelines to automate model retraining. The pipeline has three steps: data extraction from B…
- A data science team uses Vertex AI Pipelines to automate retraining. They want to ensure that only models with performan…
- A company needs to process real-time clickstream data and store it in a data warehouse for SQL-based analytics. The data…
- The exhibit shows an IAM policy for a BigQuery dataset. A Dataflow job is failing with 'Access Denied: Table ... User do…
Last reviewed: Jun 30, 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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.