PDE Ingesting and Processing the Data Practice Question
A financial firm ingests trade confirmations from a partner's SFTP server into Cloud Storage, then loads them into BigQuery. The partner drops a variable number of files at unpredictable times, and the firm must detect each new file within seconds and trigger a downstream Cloud Run job. The files must not be processed twice if the trigger fires more than once. Which design should you implement?
⚠ Common exam trap
The trap here is assuming that a Cloud Storage event fires exactly once per object, when delivery is at-least-once and the same object can generate repeated triggers that must be reconciled by a durable idempotency key.
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
✓
Configure an Eventarc trigger on the bucket's object.finalize events to invoke Cloud Run, and have the function record the object generation in Firestore before processing.
Eventarc on object.finalize gives sub-minute, event-driven detection without polling, and the object generation number serves as a natural idempotency key because it uniquely identifies a version of the object. Writing that key to Firestore before doing the work makes duplicate deliveries harmless. Polling designs miss the latency target, and designs without a deduplication record allow the same file to be processed again on redelivery.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Schedule a Cloud Scheduler job every minute that lists the bucket and invokes Cloud Run for any object newer than the last run.
Why it's wrong here
Polling every minute introduces up to a minute of latency, which violates the seconds-level detection requirement, and the listing comparison is racy when multiple runs overlap. It also lacks a durable deduplication key, so a file could be picked up by two overlapping runs, causing the double processing the firm must avoid.
- ✗
Use a Pub/Sub topic populated by Cloud Storage notifications and subscribe with a pull subscription that Cloud Run polls on a schedule.
Why it's wrong here
Cloud Storage notifications do publish to Pub/Sub promptly, but having Cloud Run poll on a schedule reintroduces the latency of the polling interval and abandons the push delivery that makes event-driven invocation fast. The design also provides no idempotency mechanism, so a redelivered notification would still cause a file to be processed twice.
- ✗
Attach a Cloud Functions (1st gen) trigger to the bucket and let it call Cloud Run synchronously for each new object.
Why it's wrong here
This would detect uploads quickly, but nothing in the chain deduplicates events; Cloud Storage event delivery is at-least-once, so a retried function invocation would call Cloud Run again for the same object. The requirement to avoid double processing is therefore unmet, and the extra hop adds failure surface without adding a guard.
- ✓
Configure an Eventarc trigger on the bucket's object.finalize events to invoke Cloud Run, and have the function record the object generation in Firestore before processing.
Why this is correct
Eventarc delivers Cloud Storage object.finalize events within seconds of upload, satisfying the latency requirement. Because at-least-once delivery can produce duplicate events, recording the object's generation number as an idempotency key before doing work ensures a repeated trigger for the same object version is skipped, preventing double processing.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Google Cloud exam blueprint
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.