PCD Practice Test 11 — 15 Questions

Question 1

A company is designing a Bigtable schema for time-series data from millions of devices. Each device sends a reading every minute. The row key is currently 'device_id#timestamp'. The engineering team notices hot spots on a few popular devices. Which row key design change would BEST distribute writes across the cluster?

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

Accepted Answer

Append a random salt prefix to the row key. Appending a random salt prefix to the row key distributes writes across multiple tablet servers by breaking the sequential ordering of device IDs, preventing hot spots on popular devices. Bigtable sorts row keys lexicographically, so a salt prefix scatters writes across the key space, balancing load across the cluster.

Answer

Promote device ID to column family

Answer

Use reversed domain for device IDs

Answer

Use only timestamp as row key

Question 2

A company wants to use a combination of relational, document, and time-series databases to meet different workload requirements. What is this architectural pattern called?

Accepted Answer

Polyglot persistence. Polyglot persistence is the architectural pattern of using multiple, purpose-built database technologies within a single application or system, each chosen for the workload it handles best. Combining relational, document, and time-series databases is the textbook definition of this pattern. It allows each workload to use the data model and engine optimized for its access patterns.

Answer

Database replication

Answer

Multi-cloud database

Answer

Federated querying

Question 3

A developer uses the above cloudbuild.yaml. The build fails with error: 'unauthorized: You don't have the permission to push to this repository.' What is the most likely cause?

Accepted Answer

The Cloud Build service account does not have Artifact Registry Writer role. The error 'unauthorized: You don't have the permission to push to this repository' indicates that the Cloud Build service account lacks the necessary IAM permissions to push the container image to Artifact Registry. By default, Cloud Build uses the default compute engine service account (PROJECT_NUMBER-compute@developer.gserviceaccount.com) or a user-specified service account, which must have the Artifact Registry Writer role (roles/artifactregistry.writer) to push images. Without this role, the push is denied regardless of the image tag, registry URL, or project ID spelling.

Answer

The image tag 'latest' is invalid

Answer

The Docker registry URL is incorrect

Answer

The project ID 'my-project' is misspelled

Question 4

During an Oracle to PostgreSQL migration using Database Migration Service (DMS), the continuous replication fails with an error about unsupported data types. The source table uses Oracle's RAW data type. How should this be handled?

Accepted Answer

Verify DMS supports RAW to BYTEA mapping; if not, use a manual export/import for that table.. Oracle RAW is a variable-length binary type, and DMS's Oracle-to-PostgreSQL mapping may or may not include RAW→BYTEA depending on the DMS version and endpoint configuration. The correct engineering approach is to verify the documented type mapping first, and if DMS genuinely cannot handle RAW, fall back to a manual export/import for that specific table rather than altering the schema or dropping data. This preserves data integrity while keeping the rest of the migration on DMS.

Answer

Convert RAW to VARCHAR2 before migration using a trigger.

Answer

Raw data type is not supported by DMS; you must drop the column and re-add as BYTEA after migration.

Answer

Use Cloud Dataflow to transform the data as it streams.

Question 5

A company uses Cloud Spanner for a globally distributed application. They need to capture all row-level changes (inserts, updates, deletes) and publish them to Pub/Sub for downstream processing. Which Spanner feature should they use?

Accepted Answer

Spanner change streams. Spanner change streams are the native feature designed to capture row-level inserts, updates, and deletes with commit timestamps and stream them to downstream consumers. They integrate directly with Dataflow, which can read the change stream and publish to Pub/Sub. This is the purpose-built solution for CDC (change data capture) from Spanner without polling or custom triggers.

Answer

Spanner commit timestamps

Answer

Spanner mutations in Dataflow

Answer

Spanner interleaved tables

Question 6

A retail company needs a scalable NoSQL database for a mobile app with offline synchronization, real-time updates, and flexible security rules. The data model is document-based. Which Google Cloud service should they choose?

Accepted Answer

Firestore. Firestore is a fully managed, serverless NoSQL document database that provides offline support, real-time listeners, and security rules for mobile and web apps.

Answer

Memorystore for Redis

Answer

Cloud SQL

Answer

Cloud Bigtable

Question 7

A company deploys a Java application on Compute Engine with a preemptible VM instance group managed by an instance template. The application writes critical state to local SSD. After a preemption event, the new instance starts fresh and loses state. What is the best practice to ensure state persistence?

Accepted Answer

Refactor the application to write state to a persistent service like Cloud Storage. Local SSD data is ephemeral and lost on VM preemption or termination. Refactoring the application to write critical state to a persistent service like Cloud Storage ensures data durability independent of the VM lifecycle. This aligns with the best practice of designing preemptible workloads to be stateless, where state is stored externally.

Answer

Modify the startup script to recover state from a snapshot

Answer

Configure the managed instance group as stateful to preserve local SSD data

Answer

Use a regular (non-preemptible) VM instead of preemptible

Question 8

A mobile app developer wants to store user preferences and provide offline sync capabilities. The database should be serverless and automatically scale with usage. Which Google Cloud database is best suited?

Accepted Answer

Cloud Firestore. Cloud Firestore is a serverless, NoSQL document database that automatically scales with usage, making it ideal for storing user preferences and providing offline sync capabilities via its built-in offline data persistence and real-time synchronization. It supports mobile and web clients with automatic multi-region replication and strong consistency, aligning perfectly with the requirements of a mobile app developer.

Answer

Cloud Spanner

Answer

Cloud SQL

Answer

Cloud Bigtable

Question 9

A developer needs to deploy a Cloud Run service from a container image in Artifact Registry. What IAM role should be granted to the Cloud Run service account?

Accepted Answer

roles/artifactregistry.reader. The Cloud Run service account needs permission to read the container image from Artifact Registry during deployment. The `roles/artifactregistry.reader` role grants the `artifactregistry.repositories.downloadArtifacts` permission, which is required to pull the image. Without this role, the deployment fails with an access denied error.

Answer

roles/storage.objectViewer

Answer

roles/cloudbuild.builds.builder

Answer

roles/run.invoker

Question 10

A startup is building a social media application with a global user base. They need a database that can handle millions of concurrent users, provide strong consistency, and scale horizontally. They expect high write throughput and need to run complex SQL queries. Which database is most suitable?

Accepted Answer

Cloud Spanner. Cloud Spanner is the only Google Cloud database that combines horizontal scalability with strong consistency (external consistency via TrueTime) and full ANSI SQL support with ACID transactions. It is purpose-built for globally distributed, high-write-throughput OLTP workloads like a social media app with millions of concurrent users. Bigtable and Firestore sacrifice SQL or strong consistency, and AlloyDB is regional rather than globally horizontally scalable.

Answer

Cloud Bigtable

Answer

Firestore

Answer

AlloyDB

Question 11

A data engineer wants to perform version-controlled schema migrations as part of a CI/CD pipeline for a Cloud SQL for PostgreSQL database. Which tools should they use?

Accepted Answer

Liquibase or Flyway. Liquibase and Flyway are purpose-built database schema migration tools that maintain version-controlled, repeatable migration scripts, making them ideal for CI/CD pipelines. They integrate with build tools and can be invoked from Cloud Build to apply migrations to Cloud SQL for PostgreSQL in a controlled, auditable manner. Database Migration Service is for migrating data from source databases to Cloud SQL, not for ongoing schema version control.

Answer

Database Migration Service

Answer

gcloud sql import

Answer

Cloud Build and Cloud Scheduler

Question 12

A Cloud Run service experiences high latency under load. The service is a Node.js Express app that processes requests sequentially due to a global mutex. What is the most effective solution?

Accepted Answer

Remove the mutex and ensure request handling is asynchronous. The root cause is that the global mutex forces sequential processing, negating Node.js's asynchronous event loop. Removing the mutex and ensuring asynchronous request handling (e.g., using async/await or Promises) allows the single-threaded event loop to interleave I/O-bound tasks, dramatically reducing latency under concurrent load. This directly addresses the bottleneck without changing the underlying infrastructure.

Answer

Use Cloud Run for Anthos to handle load

Answer

Increase the number of CPUs per container

Answer

Increase the 'max-instances' setting

Question 13

Which TWO are benefits of using Cloud Build? (Choose two.)

Accepted Answer

It allows using custom build steps with community or private images. Cloud Build allows you to use custom build steps with community or private container images, enabling you to run arbitrary tools and scripts as part of your build pipeline. This flexibility means you are not limited to Google-provided build steps and can integrate any software that runs in a container.

Answer

It only supports Java and Go runtimes

Answer

It requires a trigger to start any build

Answer

It provides a source code repository for version control

Question 14

A team is migrating a monolithic .NET application to Cloud Run. The application uses .NET Framework 4.8 and depends on Windows-specific libraries. What is the recommended approach to containerize and deploy this application?

Accepted Answer

Port the application to .NET Core/.NET 6+ and run on Linux. Cloud Run only supports Linux containers, so a .NET Framework 4.8 application that depends on Windows-specific libraries cannot be directly deployed. The recommended approach is to port the application to .NET Core/.NET 6+ (now .NET 8/9), which is cross-platform and can run on Linux containers, enabling deployment to Cloud Run. This aligns with Google's guidance for modernizing legacy .NET applications to leverage serverless platforms.

Answer

Deploy the application on Compute Engine with Windows Server

Answer

Use Cloud Run for Anthos on a Windows node pool

Answer

Use a Windows base image and deploy to Cloud Run

Question 15

A media company wants to serve video content globally with low latency and high throughput. Which Google Cloud service is best suited?

Accepted Answer

Cloud CDN. Cloud CDN leverages Google's global edge cache network to deliver video content from locations closest to end users, minimizing latency and offloading origin servers. It integrates with Cloud Load Balancer and Cloud Storage to provide high-throughput, low-latency streaming without requiring users to manage caching infrastructure.

Answer

Cloud Load Balancer

Answer

Cloud Storage with public bucket

Answer

App Engine