PCD Practice Questions 2 — 50 Questions

Question 1

An e-commerce platform uses Cloud SQL MySQL for orders and Bigtable for session history. To provide a unified customer view, they need to join order data with recent session activity. Which approach minimises data movement while achieving low-latency queries?

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

Accepted Answer

Use Memorystore as a cache to store denormalised customer views, updated from both databases.. Memorystore (Redis) can cache frequently accessed session data from Bigtable and order data from Cloud SQL, enabling low-latency reads without moving data permanently. Dataflow is batch-oriented, Cloud Functions is not for queries, and exporting to BigQuery adds latency.

Answer

Use Dataflow to continuously join the data and write results to BigQuery, then query BigQuery.

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Use Cloud Functions to query both databases and return combined results.

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Export both databases to Cloud Storage and use BigQuery federated queries.

Question 2

A company is using Cloud Bigtable for a high-throughput write workload. They notice periodic latency spikes. Which two metrics should they monitor to diagnose the issue? (Choose two.)

Accepted Answer

Error count. Request latency directly measures performance. Error count indicates failures or throttling. CPU utilization and disk usage are less direct indicators for write spikes. However, the question asks for two metrics to diagnose latency spikes; the most relevant are request latency and error count.

Answer

Disk bytes used

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Network throughput

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CPU utilization

Question 3

A company uses Cloud SQL for MySQL and wants to achieve high availability with automatic failover across zones while minimizing data loss. Which configuration should they use?

Accepted Answer

Configure a regional Cloud SQL instance with automatic failover. A regional Cloud SQL instance with automatic failover provides synchronous replication of data between two zones within the same region, ensuring zero data loss (RPO=0) and automatic failover with minimal downtime (RTO typically under 60 seconds). This meets the requirement for high availability with automatic failover across zones while minimizing data loss.

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Enable read replicas in different zones

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Use external read replicas with a failover script

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Use Cloud SQL Enterprise Plus edition

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Enable point-in-time recovery

Question 4

A multi-region application uses Cloud Spanner. The team needs to ensure that a write is immediately visible to all subsequent reads, even those performed in different regions. Which consistency mode should they use?

Accepted Answer

Strong consistency. Strong consistency (D) ensures that once a write is acknowledged, any subsequent read, regardless of region, will reflect that write. Cloud Spanner uses the TrueTime API and Paxos-based replication to provide external consistency (a form of strong consistency) across regions, making it the correct choice for immediate global visibility.

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Eventual consistency

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Global consistency

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Bounded staleness

Question 5

A developer notices that a Cloud Function is timing out after 60 seconds. The function makes an external API call that occasionally takes longer than the timeout. What is the best practice to handle this?

Accepted Answer

Increase the timeout for the specific Cloud Function to a higher value. Cloud Functions have a configurable timeout per function (up to 540 seconds for HTTP functions). Increasing the timeout for the specific function that makes the slow external API call directly addresses the timeout issue without affecting other functions or introducing unnecessary retry overhead. This is the most targeted and efficient solution.

Answer

Implement retry logic without changing the timeout

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Increase the timeout for all Cloud Functions in the project

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Decrease the timeout to fail fast and implement retry logic

Question 6

A database team is planning to migrate a 500 GB MySQL database to Cloud SQL. They require minimal downtime. Which Database Migration Service job type should they use?

Accepted Answer

Continuous migration job. Continuous migration job performs an initial full dump and then continuously replicates changes via CDC, allowing a near-zero downtime cutover by promoting the replica.

Answer

One-time migration job

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Cloud SQL replication from external primary

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Bulk export and import

Question 7

You want to configure Cloud SQL for MySQL with high availability (HA). The application requires that failover be automatic and that the failover replica is in a different zone within the same region. Which configuration should you use?

Accepted Answer

Enable the high availability option when creating the Cloud SQL instance. Enabling the high availability (HA) option when creating a Cloud SQL for MySQL instance automatically provisions a standby replica in a different zone within the same region. This configuration provides automatic failover without manual intervention, meeting the requirement for HA with zone-level redundancy.

Answer

Use Cloud SQL with a cross-region replica and configure failover with gcloud

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Set up a Cloud SQL instance with multiple read replicas and use failover via the Cloud SQL Proxy

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Create a read replica in a different zone and configure automatic failover using a load balancer

Question 8

You manage a global ecommerce platform using Cloud Spanner. You need to support a query that joins two tables on a foreign key relationship. The tables are parent and child in an interleaved table hierarchy. Which statement about performance is TRUE?

Accepted Answer

The join will be fast because interleaving stores child rows with the parent row in the same split. Cloud Spanner interleaved tables physically co-locate child rows with their parent row within the same split (and often the same tablet). This means a join on the interleaved foreign key can be executed with minimal cross-node communication, as the data needed for the join is stored together, resulting in very fast query performance.

Answer

Interleaved tables cannot be joined

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The join will be slow because interleaving increases split overhead

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The join is only fast if you use a global secondary index

Question 9

A company is migrating a MySQL 5.7 database to Cloud SQL for MySQL 8.0. Their application uses utf8 charset and GROUP BY with nonstandard behavior (e.g., missing expressions in SELECT list). After migration, they notice queries that previously ran now fail. What is the most likely cause?

Accepted Answer

ONLY_FULL_GROUP_BY SQL mode is enabled by default in MySQL 8.0.. MySQL 5.7 allowed GROUP BY with columns not in the SELECT list by default (ONLY_FULL_GROUP_BY was off), but MySQL 8.0 enables it by default. This change can cause queries to fail if they rely on the old behavior.

Answer

The caching_sha2_password plugin changed authentication.

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JSON data type behavior changed in MySQL 8.0.

Answer

The utf8 charset is not supported in MySQL 8.0.

Question 10

A company is migrating from Snowflake to BigQuery. They have a large dataset with semi-structured data stored as VARIANT columns in Snowflake. How should they represent this data in BigQuery?

Accepted Answer

Store as ARRAY> (RECORD type) with nested fields.. Snowflake's VARIANT type is used for semi-structured data like JSON. BigQuery has the RECORD (STRUCT) and REPEATED modes for nested and repeated data, and supports JSON data type (in preview) or storing as a STRING. The best practice is to use the native RECORD type to represent the structure for query performance and ease of use.

Answer

Store as STRING and use JSON_EXTRACT functions.

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Store as JSON data type and use JSON functions for queries.

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Store as BYTES and handle encoding in application.

Question 11

A developer wants to run a single test suite across multiple environments (dev, staging, prod) using Cloud Build. What is the best practice?

Accepted Answer

Use a single Cloud Build trigger with substitutions to parameterize the environment.. Cloud Build triggers support substitutions (e.g., `$_ENV`) that allow a single trigger to parameterize the environment variable, enabling the same test suite to run across dev, staging, and prod without duplicating configuration. This aligns with Infrastructure as Code (IaC) principles and reduces maintenance overhead.

Answer

Use Cloud Deploy to run tests in each environment.

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Use separate branches for each environment.

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Create separate Cloud Build triggers for each environment.

Question 12

An organization runs a stateful application on GKE that uses PersistentVolumes. They want to perform a rolling update of the application without disrupting the underlying persistent data. What should they use?

Accepted Answer

A StatefulSet with a PersistentVolumeClaim template.. A StatefulSet is the correct choice because it is designed for stateful applications that require stable, unique network identifiers and persistent storage. By including a PersistentVolumeClaim template in the StatefulSet spec, each Pod gets its own dedicated PersistentVolume that persists across rescheduling and rolling updates, ensuring data is not disrupted.

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A ReplicaSet with a headless service.

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A DaemonSet with a PodDisruptionBudget.

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A Deployment with a PersistentVolumeClaim template.

Question 13

A company is designing a polyglot persistence architecture. They need to use Cloud SQL for transactions, Bigtable for real-time analytics, and BigQuery for reporting. They also need to keep data across these systems eventually consistent. Which TWO approaches should they use?

Accepted Answer

Implement a saga pattern with compensating transactions for each write.

Answer

Use two-phase commit across all databases.

Answer

Use Cloud Spanner as a single database to avoid polyglot complexity.

Answer

Write to all three databases in a single transaction using distributed transactions.

Question 14

You are designing a Cloud Bigtable schema for a time-series application. To optimize performance and avoid hot spots, which THREE row key design practices should you follow? (Choose 3)

Accepted Answer

Place the highest cardinality field (e.g., device ID) first in the row key. Reversing timestamps, salting keys, and promoting high-cardinality fields to the start of the row key are recommended to distribute writes evenly.

Answer

Use a single table for all data

Answer

Use sequential integers as row keys

Question 15

You need to migrate an on-premises MySQL 5.7 database (2 TB) to Cloud SQL for MySQL with minimal downtime. Database Migration Service (DMS) is chosen. What is the correct sequence of steps to ensure a successful continuous migration?

Accepted Answer

Set up a connection profile for the source, create a DMS migration job (full dump + CDC), monitor the initial dump, then promote the replica to complete migration.. DMS continuous migration first performs a full dump (initial snapshot), then switches to CDC to replicate ongoing changes. After the initial dump, you validate the replica and promote it to make it the primary. The correct order: create connection profile for source, create migration job with full dump + CDC, monitor initial dump, then promote when ready.

Answer

Use mysqldump to export the database, import to Cloud SQL, then set up DMS for CDC only.

Answer

Create a DMS continuous migration job directly without a connection profile.

Answer

First promote the Cloud SQL replica, then create the connection profile.

Question 16

An online gaming platform uses Cloud Spanner as its globally distributed database. They notice that write latency increases significantly during peak hours. The application performs many single-row writes with high consistency requirements. Which design change would most effectively reduce write latency?

Accepted Answer

Use interleaved tables to colocate related rows.. Interleaved tables in Cloud Spanner physically colocate parent and child rows, reducing the number of splits and cross-node round trips for related single-row writes. This minimizes distributed transaction overhead and write latency, especially under high consistency requirements, without requiring additional nodes or sacrificing consistency.

Answer

Increase the number of nodes in the Spanner instance.

Answer

Switch to eventual consistency mode for writes.

Answer

Split the table into multiple smaller tables.

Question 17

Match each Google Cloud service to its primary purpose.

Accepted Answer

Cloud Run: A fully managed compute platform for containerized applications.. Cloud Run deploys containers, Cloud Functions runs event-driven functions, and Cloud Storage stores unstructured objects. Common confusions include swapping the definitions of Cloud Run and Cloud Functions, or mistaking Cloud Storage for a database service like Cloud SQL.

Answer

Cloud Run: A serverless execution environment for building and connecting cloud services.

Answer

Cloud Storage: A fully managed relational database for MySQL, PostgreSQL, and SQL Server.

Question 18

A team uses Cloud Build to build and deploy a Node.js application to App Engine flexible environment. The build succeeds, but the deployment fails with 'ERROR: (gcloud.app.deploy) Error Response: [9] Application startup error!' The team checks logs and sees 'Error: Module not found: 'express''. What is the most likely cause?

Accepted Answer

The dependencies are not installed during the build step before deploying.. The error 'Module not found: express' indicates that the Node.js dependencies (specifically the 'express' package) are not present in the deployed application. In Cloud Build, the build steps must explicitly install dependencies (e.g., via 'npm install') before the deploy step. If the build configuration does not include an 'npm install' step, the dependencies listed in package.json are not copied to the App Engine flexible environment, causing the startup error.

Answer

The build step includes 'npm test' which fails.

Answer

The Node.js version specified in app.yaml is incompatible with the dependencies.

Answer

The app.yaml file is missing from the root of the repository.

Question 19

You are migrating an on-premises Oracle database to Cloud SQL for PostgreSQL. You need to assess the migration feasibility and convert the schema. Which tools should you use?

Accepted Answer

Use Ora2Pg for schema conversion and DMS for data migration.. Ora2Pg is an open-source tool that converts Oracle schema to PostgreSQL. Database Migration Service (DMS) supports migration from Oracle to Cloud SQL for PostgreSQL. For assessment, you can use tools like Oracle Migration Toolkit or Ora2Pg's assessment mode.

Answer

Use mysqldump to export and import to PostgreSQL.

Answer

Use pg_dump to export the Oracle database and import into Cloud SQL.

Answer

Use DMS directly with Oracle source; it automatically converts schema.

Question 20

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

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Cloud SQL

Answer

Cloud Bigtable