PDE Designing Data Processing Systems Practice Question
A company wants to use Pub/Sub Lite to reduce costs for a high-throughput, low-latency streaming pipeline. However, they have a requirement to retain messages for up to 7 days for reprocessing. Which Pub/Sub Lite configuration supports this retention?
⚠ Common exam trap
Google often tests the distinction between topic-level and subscription-level retention in Pub/Sub Lite, where candidates mistakenly assume subscriptions control retention (as in standard Pub/Sub) rather than the topic itself.
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
✓
Set the retention duration on the Pub/Sub Lite topic to 7 days
Pub/Sub Lite topics are the only entity where retention duration is configured; messages are retained in the topic's storage for the specified duration, allowing subscribers to replay messages within that window. Setting the retention duration to 7 days on the topic ensures messages are available for reprocessing for up to 7 days, meeting the requirement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Set the retention duration on the Pub/Sub Lite topic to 7 days
Why this is correct
Pub/Sub Lite topics allow setting message retention duration up to 7 days. Messages are retained in the topic's storage and can be re-delivered to subscriptions within that period.
- ✗
Set the retention duration on the Pub/Sub Lite subscription to 7 days
Why it's wrong here
Pub/Sub Lite does not have per-subscription retention; retention is set on the topic. Subscriptions can have a retention duration, but in Pub/Sub Lite, topic retention is the primary setting.
- ✗
Enable exactly-once delivery on the Pub/Sub Lite topic to retain messages for 7 days
Why it's wrong here
Exactly-once delivery does not extend retention; it ensures messages are not duplicated.
- ✗
Use a Pub/Sub Lite reservation with 7-day retention
Why it's wrong here
Reservations allocate capacity (throughput) but do not affect message retention.
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