PDE Designing Data Processing Systems Practice Question
A company needs to process high-throughput streaming data with low latency. They are considering Cloud Pub/Sub for ingestion and Cloud Dataflow for processing. However, they are concerned about cost. Which alternative to Cloud Pub/Sub would reduce costs while still meeting the throughput requirements?
⚠ Common exam trap
PDE often tests the misconception that pull or push subscriptions are cost-saving alternatives, when they are merely delivery methods for standard Pub/Sub, and confuses Cloud Tasks with a streaming ingestion service.
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
✓
Cloud Pub/Sub Lite
Cloud Pub/Sub Lite is a zonal, cost-optimized messaging service designed for high-throughput streaming with predictable, low latency. Unlike standard Pub/Sub, which replicates data across zones and charges for data transfer and storage, Pub/Sub Lite lets you choose a capacity (in MiB/s) and charges a flat hourly rate, significantly reducing costs for steady, high-volume workloads. It integrates with Cloud Dataflow via the Pub/Sub Lite I/O connector, so the processing pipeline remains viable. Thus, it meets the throughput and latency requirements while addressing cost concerns.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Cloud Pub/Sub with pull subscriptions
Why it's wrong here
Pull subscriptions alter how consumers retrieve messages, not the per-message ingestion charge, so cost is identical. Pull is chosen when subscribers control their own flow and acknowledgement timing, for example batch consumers with long processing windows.
- ✗
Cloud Tasks
Why it's wrong here
Cloud Tasks queues discrete asynchronous tasks with rate and retry controls, not continuous high-throughput event streams, so it cannot absorb the required volume. It is chosen for dispatching individual HTTP callbacks to workers, not for streaming ingestion.
- ✓
Cloud Pub/Sub Lite
Why this is correct
Pub/Sub Lite provides the same high-throughput, low-latency ingestion as Pub/Sub but at a substantially lower cost, because it trades away automatic multi-zone replication and requires you to provision capacity in a specific zone. That trade-off satisfies the throughput requirement while directly addressing the stated cost concern.
- ✗
Cloud Pub/Sub with push subscriptions
Why it's wrong here
Push subscriptions change delivery to a subscriber endpoint, not the ingestion cost model; per-message and throughput pricing is unchanged. Push is chosen when you want Pub/Sub to initiate delivery to an HTTPS endpoint without a polling client.
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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.