PCDE Practice Question: Manage a solution that can span multiple database technologies

A financial services company uses Cloud Spanner for transaction processing. They need to capture real-time changes from the database to stream to a downstream analytics system. Which THREE services or features can achieve this?

⚠ Common exam trap

Candidates often confuse services that capture changes (Spanner change streams) with services that transport or process those changes (Pub/Sub, Dataflow), leading to incorrect selections like Bigtable replication or Cloud SQL, which serve different purposes.

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

Spanner change streams are correct because they capture row-level mutations in real time directly from Cloud Spanner. Cloud Pub/Sub is correct as it provides a fully managed messaging service that ingests and delivers change events from Spanner change streams to downstream systems with at-least-once delivery and low latency. Cloud Dataflow is correct because it can process and transform the change stream events in real time, enabling streaming analytics or integration with other services. Together, these three services form a complete pipeline: Spanner change streams capture changes, Pub/Sub transports them, and Dataflow processes them for the analytics system.

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 SQL for PostgreSQL
Why it's wrong here
Cloud SQL is a separate service, not used to read Spanner changes.
✓
Cloud Pub/Sub
Why this is correct
Pub/Sub can deliver change stream events to subscribers.
✗
Bigtable replication
Why it's wrong here
Bigtable replication is for Bigtable, not Spanner.
✓
Spanner change streams
Why this is correct
Change streams provide a log of mutations.
✓
Cloud Dataflow
Why this is correct
Dataflow can read change streams and stream to analytics.

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Same concept, more angles

4 more ways this is tested on PCDE

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A company uses Cloud Spanner for a global application. They need to capture real-time changes to certain tables for downstream processing. Which two services or features can be used together to achieve this? (Choose TWO.)

medium

✓ A.Spanner change streams
B.Cloud Pub/Sub Lite
C.Cloud SQL for PostgreSQL
D.Cloud Functions
✓ E.Cloud Dataflow

Why A: Spanner change streams capture transactional changes in near real-time. Dataflow can read from change streams and stream the changes to downstream systems like Pub/Sub, BigQuery, or Cloud Storage.

Variation 2. Your company runs a global e-commerce platform on Cloud Spanner. You need to capture real-time changes to a table (e.g., orders) and stream them to a downstream analytics pipeline in near real-time. Which TWO Google Cloud features or services should you combine to achieve this? (Choose two.)

hard

A.Cloud Functions
✓ B.Dataflow streaming pipeline
C.Cloud Pub/Sub
D.Cloud SQL for PostgreSQL
✓ E.Cloud Spanner change streams

Why B: A Dataflow streaming pipeline can consume Cloud Spanner change streams in near real-time, process the data (e.g., transform, filter, aggregate), and write it to a downstream analytics system. Dataflow provides exactly-once processing semantics and auto-scaling, making it ideal for continuous change data capture (CDC) pipelines.

Variation 3. A company uses Cloud Spanner and needs to capture real-time changes from a table for downstream processing. They want to avoid writing custom application code to track changes. Which THREE components should they use? (Choose three.)

hard

A.Cloud Bigtable
✓ B.Pub/Sub
✓ C.Change Streams
D.Cloud Spanner API
✓ E.Dataflow

Why B: Cloud Spanner Change Streams (option C) capture real-time changes (inserts, updates, deletes) from a table. These changes are automatically published to a Pub/Sub topic (option B). A subscriber can then use Dataflow (option E) to process the change stream messages for downstream transformations or loading. Cloud Bigtable (option A) is a different database service not involved in this scenario. The Cloud Spanner API (option D) is not needed because Change Streams already integrate with Pub/Sub.

Variation 4. A company uses Cloud Spanner and needs to implement change data capture (CDC) to stream changes to a downstream analytics pipeline. Which two features can they use? (Choose TWO.)

medium

✓ A.Pub/Sub integration to consume change stream data
B.Cloud SQL for PostgreSQL logical replication
C.Datastream
D.Bigtable replication
✓ E.Spanner change streams

Why A: Spanner change streams capture row-level changes in a Cloud Spanner database. These changes can be consumed via Pub/Sub integration, allowing downstream analytics pipelines to process the data. Therefore, Option E (Spanner change streams) is correct for capturing the changes, and Option A (Pub/Sub integration) is correct for streaming them. Option B (Cloud SQL for PostgreSQL logical replication) is not applicable as it is for Cloud SQL, not Spanner. Option C (Datastream) is used for database migrations and replication, not for CDC from Spanner. Option D (Bigtable replication) is for Bigtable, not Spanner.

Last reviewed: Jul 4, 2026

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