PCD Practice Test 25 — 15 Questions

Question 1

A company is designing a polyglot persistence architecture for a social media platform. They need to store user profiles (relational), posts (document), and activity logs (time-series). Which THREE Google Cloud databases should they choose for these respective workloads?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Cloud SQL. Cloud SQL (or Spanner) for relational user profiles, Firestore for document posts, and Bigtable for time-series activity logs. Memorystore is a cache, not persistent. Cloud Storage is object storage.

Answer

Cloud Storage

Answer

Memorystore

Question 2

A media company uses Cloud SQL for MySQL for its user data and needs to export daily snapshots to BigQuery for reporting. The reporting must reflect data as of midnight UTC. Which approach is most cost-effective and efficient?

Accepted Answer

Export Cloud SQL data to Cloud Storage using a daily Cloud Scheduler job, then load into BigQuery.. Using Cloud SQL export to Cloud Storage (SQL dump) and then loading into BigQuery is simple and cost-effective for daily snapshots. Using Datastream would be overkill and more expensive for a daily batch. Federated queries would incur repeated query costs and may not be as fresh.

Answer

Use Cloud SQL managed backups and read from the backup files directly.

Answer

Use Datastream to continuously replicate data to BigQuery and query BigQuery tables.

Answer

Use BigQuery federated queries to connect directly to Cloud SQL.

Question 3

A company needs to query data across Cloud SQL (MySQL) and Bigtable using BigQuery without moving the data. Which TWO configurations are required?

Accepted Answer

Create an external table in BigQuery that references the Bigtable table using a Bigtable URI.

Answer

Enable BigQuery Omni for cross-cloud querying.

Answer

Use Dataflow to replicate Cloud SQL and Bigtable data to BigQuery.

Answer

Create a BigQuery dataset in the same region as Cloud SQL and Bigtable.

Question 4

A company uses Cloud SQL for MySQL and wants to set up cross-region disaster recovery with automated failover. Which two steps are required? (Choose 2)

Accepted Answer

Create a cross-region read replica with failover enabled.. Enabling automated backups and cross-region copies ensures data is available in another region. Configuring a cross-region read replica with failover capability provides a DR instance that can be promoted in a disaster. Point-in-time recovery is for granular restore, not failover.

Answer

Use Database Migration Service to continuously replicate to another region.

Answer

Deploy Cloud SQL in HA configuration within the same region.

Answer

Set up point-in-time recovery (PITR) with 7-day retention.

Question 5

An organization is using Cloud Spanner for a global application. They need to capture all data changes (inserts, updates, deletes) in a Spanner table and stream them to Pub/Sub for downstream processing. Which feature should they use?

Accepted Answer

Cloud Spanner change streams. Cloud Spanner change streams can capture row-level changes and publish them to Pub/Sub via Dataflow or direct integration.

Answer

Datastream for Spanner

Answer

Cloud Bigtable change data capture

Answer

Cloud SQL publication with pglogical

Question 6

A company uses Firestore for a mobile app. They want to implement security rules that allow users to create documents only if they are authenticated and the document's 'owner' field matches their UID. Additionally, they want to allow reads of any document where the 'visibility' field is 'public'. Which TWO conditions should the rules include?

Accepted Answer

allow read: if resource.data.visibility == 'public';. The create rule should check authentication and that the incoming document's owner matches the UID. The read rule should allow if visibility is public. Using get() for the existing document is not needed for create because request.resource refers to the new document. For read, resource.data refers to the existing document.

Answer

allow create: if resource.data.owner == request.auth.uid;

Answer

allow read: if request.resource.data.visibility == 'public';

Answer

allow write: if request.auth.uid != null;

Question 7

A global gaming company uses Cloud Spanner for player profiles and leaderboards. They want to replicate leaderboard changes to a secondary Cloud Spanner instance in another region for disaster recovery, with minimal latency. They need to ensure that all writes are eventually consistent across instances. Which THREE approaches should they consider?

Accepted Answer

Use Cloud Spanner's built-in global replication by creating a multi-region instance spanning both regions.. Spanner change streams can capture mutations and replicate to another instance via Pub/Sub and Dataflow. Spanner's built-in replication across regions provides strong consistency but not active-active across different instances. Using application dual-writes is error-prone. BigQuery is not suitable for operational replication.

Answer

Write application code that writes to both Spanner instances in each transaction (dual-writes).

Answer

Export Spanner data to BigQuery and use federated queries in the secondary region.

Question 8

A company uses Cloud Spanner for a globally distributed application. They need to capture all data changes from a critical Spanner table and stream them to Pub/Sub in real-time for downstream processing. Which approach meets this requirement?

Accepted Answer

Use Spanner change streams with a Dataflow pipeline that reads the change stream and publishes each change to a Pub/Sub topic.

Answer

Enable Spanner change streams on the table, then create a Pub/Sub subscription to consume changes directly.

Answer

Configure Spanner to export change logs to GCS and set up a Cloud Function to publish them to Pub/Sub.

Answer

Use Spanner commit timestamps and Cloud Scheduler to periodically query recent changes and publish to Pub/Sub.

Question 9

A data engineering team needs to replicate data from a PostgreSQL database to BigQuery in near real-time for analytics. Which Google Cloud service is most suitable for this task with minimal setup?

Accepted Answer

Datastream. Datastream is a serverless CDC replication service specifically designed for replicating from sources like PostgreSQL, MySQL, and Oracle to BigQuery, Cloud Storage, or Pub/Sub. It handles schema mapping and initial backfill.

Answer

Cloud SQL for PostgreSQL

Answer

Cloud Data Fusion

Answer

Cloud Composer

Question 10

An e-commerce company uses Cloud SQL for MySQL for transactional data and BigQuery for analytics. They need to replicate order data from Cloud SQL to BigQuery in near real-time with minimal latency. Which Google Cloud service should they use?

Accepted Answer

Datastream. Datastream is a serverless CDC replication service that can stream changes from MySQL (including Cloud SQL) to BigQuery, GCS, or Pub/Sub with low latency. Dataflow requires building pipelines, DMS is for database migrations (not ongoing sync), and Pub/Sub alone doesn't load into BigQuery.

Answer

Cloud Dataflow

Answer

Cloud Pub/Sub

Answer

Database Migration Service (DMS)

Question 11

A team runs a microservice on Compute Engine behind a regional external HTTP load balancer. They want to automatically replace unhealthy instances without manual intervention. Which feature should they use?

Accepted Answer

Managed instance group with autoscaling and health check. A managed instance group (MIG) with autoscaling and a health check is the correct choice because it automatically replaces unhealthy instances based on the health check results. The MIG uses the health check to detect failed instances, then automatically recreates them from the instance template, ensuring high availability without manual intervention. Autoscaling further adjusts the number of instances based on load, but the core replacement mechanism is driven by the MIG's health check and autohealing feature.

Answer

Unmanaged instance group with health check

Answer

Instance template with manual replacement

Answer

Load balancer backend service health check only

Question 12

A company has a Cloud SQL for MySQL instance in the us-central1 region. They want to improve read performance for a report generation tool that runs in us-west1, and also provide disaster recovery in case the primary fails. Which TWO actions should they take?

Accepted Answer

Configure the report generation tool to connect to the cross-region replica.. Cross-region read replicas serve both read scaling in another region and disaster recovery. A regional HA instance only provides HA within the same region. Increasing machine type improves performance but not DR. Creating a read replica in the same region does not help with cross-region DR.

Answer

Enable high availability (HA) on the primary instance.

Answer

Change the primary instance to a larger machine type.

Answer

Add a read replica in us-central1.

Question 13

An engineer needs to create a cross-region read replica for a Cloud SQL for MySQL instance for disaster recovery. Which step is required?

Accepted Answer

Create the replica in a different region. Cross-region read replicas are supported in Cloud SQL for MySQL. The engineer can create a read replica in a different region from the primary instance. Read replicas are promoted for DR. HA configuration is regional only. External replicas are for on-premises. Binary logging must be enabled on the primary.

Answer

Create the replica in a different zone within the same region

Answer

Configure an external replica in the target region

Answer

Enable HA on the primary instance first

Question 14

A startup is building a mobile app that needs offline support and real-time synchronization across devices. The data is primarily user profiles and activity logs. Which Google Cloud database would best meet these requirements?

Accepted Answer

Firestore. Firestore provides offline data persistence and real-time sync, making it ideal for mobile apps. Cloud SQL and Spanner lack built-in offline support, and Bigtable is not suitable for complex document data.

Answer

Cloud Spanner

Answer

Cloud SQL

Answer

Cloud Bigtable

Question 15

A company is using Cloud Bigtable for a time-series application. They need to ensure that if one zone fails, the database remains available for reads and writes with minimal downtime. Which configuration should they use?

Accepted Answer

Add a secondary cluster in a different zone within the same region. Adding a secondary cluster in a different zone within the same region provides replication and automatic failover for both reads and writes.

Answer

Enable auto-scaling on the cluster

Answer

Use a development instance type

Answer

Use a single-cluster instance with SSD storage