PDE Designing Data Processing Systems Practice Question
Your company ingests millions of events per second into a Pub/Sub topic. The downstream consumer must process events with minimal latency and high throughput. However, the consumer occasionally falls behind during traffic spikes, and you need to ensure no data loss while minimizing costs. Which subscription type and configuration should you choose?
⚠ Common exam trap
PDE often tests the misconception that push subscriptions are always better for low latency, but pull with flow control provides better backpressure and cost control for high-throughput, spiky workloads.
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
✓
Pull subscription with flow control settings
A pull subscription with flow control settings allows the consumer to control the rate of message delivery, preventing overload during traffic spikes. Pull subscriptions are ideal for high-throughput, low-latency processing because the consumer can batch and process messages at its own pace. Flow control settings (e.g., max outstanding messages, max bytes) help avoid overwhelming the consumer, ensuring no data loss while minimizing costs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Push subscription with a load balancer
Why it's wrong here
A push subscription with a load balancer adds an intermediary hop and requires the endpoint to acknowledge each message; during spikes, unacknowledged pushes are retried, but Pub/Sub push has no built-in buffering for slow consumers. Push suits low-latency webhook delivery to autoscaled services.
- ✓
Pull subscription with flow control settings
Why this is correct
A pull subscription lets the consumer control retrieval rate, and flow control settings cap outstanding messages and bytes so the subscriber is not overwhelmed during spikes. Pub/Sub retains unacknowledged messages, so throttled consumption prevents data loss while avoiding the cost of over-provisioned resources.
- ✗
Push subscription with endpoint on Cloud Run
Why it's wrong here
Cloud Run push endpoints scale on request concurrency, but Pub/Sub push flow control is limited; during spikes, messages are redelivered rather than queued for later, risking duplicate processing and cost from retries. Push suits event-driven, latency-sensitive workloads with fast acknowledgements.
- ✗
Pull subscription with exactly-once delivery disabled
Why it's wrong here
Disabling exactly-once delivery does not address the retention requirement; a pull subscription still risks message expiry during prolonged spikes unless the retry policy and message retention are extended, which raises cost. Pull suits high-throughput batch consumers, not latency-sensitive push delivery.
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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.