PDE Ingesting and Processing the Data Practice Question
Which BigQuery feature allows you to write data with exactly-once semantics, high throughput, and the ability to buffer data before making it available for queries?
⚠ Common exam trap
A common trap is assuming that legacy streaming inserts (option C) provide exactly-once semantics, but they actually offer at-least-once delivery. The Storage Write API with buffered mode is the only correct choice for exactly-once, high-throughput, buffered writes.
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
✓
Storage Write API with buffered mode
The Storage Write API with buffered mode (option D) is correct because it provides exactly-once semantics for data ingestion, high throughput via gRPC streaming, and the ability to buffer data in memory before making it available for queries. This mode allows you to commit rows in a stream, ensuring no duplicates, while the buffering stage gives you control over when data becomes visible in BigQuery.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
BigQuery load jobs
Why it's wrong here
Load jobs are batch operations; they provide atomicity per job but no streaming exactly-once semantics or buffering before query visibility. Batch loading is tempting because it writes data reliably, yet the scenario describes the Storage Write API, which supports streaming commits and buffered availability.
- ✗
BigQuery Data Transfer Service
Why it's wrong here
Data Transfer Service moves data on a schedule from external sources into BigQuery; it offers neither streaming exactly-once semantics nor a write buffer. It is tempting because it ingests data, but the described behaviour matches the Storage Write API, not scheduled transfer jobs.
- ✗
Legacy streaming inserts
Why it's wrong here
Legacy streaming inserts offer at-least-once delivery, so duplicate rows can appear; they also lack the buffering stage that the Storage Write API's pending mode provides. They suit simple, low-cost real-time dashboards where occasional duplicates are tolerable, not exactly-once pipelines.
- ✓
Storage Write API with buffered mode
Why this is correct
Storage Write API's buffered mode holds records in a stream until you commit them, delivering exactly-once semantics through stream-level offsets and deduplication. This satisfies the stem's requirement to buffer data before query visibility, while sustaining high throughput — unlike the legacy streaming API, which inserts rows immediately.
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