PCD Practice Test 17 — 15 Questions

Question 1

You are configuring Cloud Bigtable for a financial market data application. Write throughput is critical, and row keys are based on stock symbols. You notice significant write latency on a few nodes. What is the most effective way to improve write distribution?

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

Accepted Answer

Prepend a hashed prefix to the row key (salted keys). Bigtable distributes data across nodes by row-key ranges, so a monotonically increasing or highly clustered key (like stock symbols starting with similar letters) concentrates writes on a few tablets and nodes. Prepending a hashed prefix (salting) spreads rows across the keyspace, balancing write load across all nodes. This directly addresses the write-latency hotspot caused by uneven key distribution.

Answer

Separate frequently accessed columns into a different column family

Answer

Increase the garbage collection (GC) grace period

Answer

Use reversed domain keys (e.g., com.example.stock)

Question 2

A company uses Cloud SQL for MySQL to store customer data. They have enabled automatic backups and a read replica for reporting. The application experiences timeouts during peak hours because the primary instance cannot handle the write load. The team needs to improve write performance without losing the ability to read from replicas. What should they do?

Accepted Answer

Increase the number of vCPUs on the primary instance.. Increasing the number of vCPUs on the primary Cloud SQL for MySQL instance directly improves its processing capacity to handle higher write throughput. This addresses the root cause of timeouts during peak hours without disrupting the existing read replica architecture, which continues to serve reporting queries. Cloud SQL allows vertical scaling of the primary instance by adjusting machine type, and this change does not affect the ability to read from replicas.

Answer

Increase the size of the read replica to handle writes.

Answer

Promote the read replica to a standalone instance and redirect writes.

Answer

Use Cloud Spanner instead of Cloud SQL for better write scalability.

Question 3

A company is migrating an Oracle database to Cloud SQL for PostgreSQL using Ora2Pg. They need to convert stored procedures and functions. After conversion, they find that some PL/SQL code is not working. What is the most likely reason?

Accepted Answer

Ora2Pg does not convert Oracle-specific PL/SQL packages like DBMS_*.. Ora2Pg is an open-source tool that automates migration from Oracle to PostgreSQL, but it does not convert Oracle-specific PL/SQL packages such as DBMS_*, UTL_*, or other built-in Oracle libraries. These packages have no direct equivalent in PostgreSQL, so any stored procedures or functions that rely on them will fail after conversion. Manual rewriting or using PostgreSQL-compatible extensions (e.g., pg_dbms_* community modules) is required.

Answer

pgTap is needed to validate the converted code.

Answer

The Database Migration Service is required to convert stored procedures.

Answer

The PostgreSQL target instance is running an incompatible version.

Question 4

Which TWO security best practices should be implemented when using Cloud Build to deploy applications? (Choose 2.)

Accepted Answer

Use Cloud KMS to encrypt sensitive environment variables.. Cloud Build does not automatically encrypt environment variables stored in build config files or the console. Using Cloud KMS allows you to encrypt sensitive data like API keys or passwords, then decrypt them at build time via the `gcloud kms decrypt` step, ensuring secrets are never stored in plaintext.

Answer

Add SSH keys to Cloud Build for private Git repos.

Answer

Use container image tags instead of digests in build configs.

Answer

Store secrets in Cloud Build's default substitution variables.

Question 5

A company wants to run analytics queries on Cloud SQL data without impacting the transactional workload. They need to query the Cloud SQL database directly from BigQuery. Which BigQuery feature should they use?

Accepted Answer

BigQuery federated queries using Cloud SQL external table. BigQuery federated queries using Cloud SQL external tables allow you to query Cloud SQL databases directly from BigQuery without moving or replicating the data. This feature uses a federated query engine that pushes down SQL operations to Cloud SQL, minimizing the impact on the transactional workload by only reading the required data on demand.

Answer

Cloud SQL read replicas

Answer

Datastream to replicate Cloud SQL to BigQuery

Answer

BigQuery Omni

Question 6

A team deploys a containerized application on Cloud Run and notices increased latency during traffic spikes due to cold starts. Which configuration change would best address this?

Accepted Answer

Set min_instances to a value greater than 0. Setting min_instances to a value greater than 0 keeps a minimum number of container instances warm, eliminating cold starts during traffic spikes. Cloud Run scales to zero by default, so requests during idle periods trigger cold starts; maintaining at least one instance ensures immediate response. This directly addresses latency caused by cold starts.

Answer

Set concurrency to 1

Answer

Enable CPU always allocated

Answer

Increase max_instances

Question 7

Which Google Cloud database is a serverless data warehouse designed for analytical queries on petabyte-scale data, with SQL interface and built-in machine learning capabilities?

Accepted Answer

BigQuery. BigQuery is Google Cloud's fully managed, serverless data warehouse designed for petabyte-scale analytical queries using standard SQL. It includes BigQuery ML, which allows you to build and train machine learning models directly using SQL, matching the question's description exactly.

Answer

AlloyDB

Answer

Cloud Bigtable

Answer

Cloud Spanner

Question 8

An engineer needs to configure Firestore security rules for a mobile app where users can only read and write their own data. The user's UID is stored in the document field 'owner'. Which rule correctly restricts access?

Accepted Answer

allow read, write: if resource.data.owner == request.auth.uid;. In Firestore security rules, the authenticated user's UID is exposed as `request.auth.uid`. Comparing `resource.data.owner` (the document field) to `request.auth.uid` correctly restricts each user to documents they own.

Answer

allow read, write: if resource.data.owner == request.auth.name;

Answer

allow read, write: if resource.data.owner == request.auth.userId;

Answer

allow read, write: if resource.data.userId == request.auth.uid;

Question 9

A startup is building a mobile application with real-time synchronization across user devices. They expect millions of users and need a NoSQL database with offline support and real-time listeners. Which database should they choose?

Accepted Answer

Firestore. Firestore is a serverless NoSQL document database that provides real-time listeners and offline support for mobile and web applications. It is designed to scale to millions of users and synchronize data across devices automatically, making it the ideal choice for this use case.

Answer

Cloud Bigtable

Answer

BigQuery

Answer

Cloud SQL

Question 10

A company wants to use Firestore security rules to allow users to read documents only if they are the owner (user ID matches the 'owner' field in the document). Which rule is correct?

Accepted Answer

allow read: if resource.data.owner == request.auth.uid;. The correct rule is `allow read: if resource.data.owner == request.auth.uid;`. This checks that the 'owner' field in the document matches the authenticated user's UID. Firestore security rules use `request.auth.uid` to represent the unique user ID, and `resource.data` to access the document's data. This ensures that only the owner can read the document.

Answer

allow read: if resource.data.uid == request.auth.token.email;

Answer

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

Answer

allow read: if request.auth.uid == 'owner';

Question 11

A company runs a microservices application on Google Kubernetes Engine (GKE). Users report intermittent slow responses. Developers suspect a specific service is causing latency. Which Google Cloud tool should they use to trace requests across services and identify the root cause?

Accepted Answer

Cloud Trace. Cloud Trace is the correct tool because it provides distributed tracing capabilities that capture end-to-end latency data as requests propagate through microservices. By analyzing trace spans and their timing, developers can pinpoint which specific service is introducing delay, directly addressing the intermittent slow responses described.

Answer

Cloud Debugger

Answer

Cloud Monitoring

Answer

Cloud Logging

Question 12

An organization has Cloud Bigtable for real-time ad serving and BigQuery for analytics. They want to synchronize data changes from Bigtable to BigQuery every hour with a Dataflow pipeline. However, they notice that some updates are missed. What is the most likely cause?

Accepted Answer

Bigtable does not support change data capture natively. Cloud Bigtable does not natively support change data capture (CDC) or change streams, so a Dataflow pipeline cannot reliably capture every row mutation. Without a change log, the pipeline must poll or scan, which misses updates that occur between reads. This is the root cause of missed updates.

Answer

The Dataflow pipeline reads from Bigtable using a snapshot read

Answer

The Bigtable table has no primary key

Answer

The Dataflow pipeline is using the wrong sink

Question 13

A company has a monolithic application that needs to be migrated to Cloud Run. The application currently writes logs to a local file. What is the best practice for handling logs in Cloud Run?

Accepted Answer

Write logs to stdout and stderr; Cloud Run automatically sends them to Cloud Logging.. Cloud Run is a serverless compute platform that automatically integrates with Cloud Logging. The best practice is to write logs to stdout and stderr because Cloud Run's runtime captures these streams and forwards them to Cloud Logging without any additional agents or sidecars. This approach aligns with the 12-factor app methodology and ensures logs are available for monitoring and troubleshooting.

Answer

Use a third-party logging agent installed in the container image.

Answer

Use a sidecar container to ship logs to Stackdriver.

Answer

Continue writing to a local file; Cloud Run will persist it.

Question 14

A financial services company is building a global payment system that requires strong ACID transactions across multiple regions, with 99.999% availability and automatic failover. Which Google Cloud database should they choose?

Accepted Answer

Cloud Spanner. Cloud Spanner is the only Google Cloud database that provides strong ACID transactions across multiple regions with 99.999% availability and automatic failover. It uses a globally distributed architecture with synchronous replication and the TrueTime API to ensure external consistency, making it ideal for a global payment system that requires strict consistency and high availability.

Answer

AlloyDB with cross-region replicas

Answer

Cloud SQL with cross-region replicas

Answer

Firestore in Native mode

Question 15

A developer is designing a Cloud Spanner schema for a blog application with tables: Posts (PostId, AuthorId, Title, Content) and Comments (CommentId, PostId, Author, Text). They want to store comments near their parent post for efficient retrieval. Which schema design should they use?

Accepted Answer

Use interleaving: define Comments as an interleaved table with Posts, with Comments primary key (PostId, CommentId). Interleaved tables in Cloud Spanner allow storing child rows (Comments) physically near parent rows (Posts) if the child table's primary key includes the parent's primary key. This improves locality and reduces cross-split reads.

Answer

Create a separate Comments table without interleaving and use application-level caching

Answer

Store comments as a JSON array within the Posts table

Answer

Use a foreign key from Comments to Posts and create a global secondary index on PostId