PCD Practice Test 19 — 15 Questions

Question 1

A company is migrating an on-premises PostgreSQL OLTP application to Google Cloud. They need a managed database with high availability, automatic failover, and zero RPO. Which database service should they choose?

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

Accepted Answer

Cloud SQL for PostgreSQL with HA configuration. Cloud SQL for PostgreSQL supports HA instances with synchronous replication to a standby in the same region, automatic failover, and zero RPO. It is the best choice for a lift-and-shift of a PostgreSQL OLTP workload.

Answer

Firestore

Answer

Bigtable

Answer

Cloud Spanner

Question 2

A startup is building an application that requires strong consistency and horizontal scalability across multiple regions. They need a fully managed relational database that supports both SQL queries and ACID transactions. Which database service should they choose?

Accepted Answer

Cloud Spanner. Cloud Spanner is the only fully managed relational database on GCP that offers strong consistency and horizontal scalability across regions. It supports SQL and ACID transactions. Cloud SQL is regionally limited and does not auto-scale horizontally.

Answer

Cloud SQL

Answer

Firestore

Answer

Bigtable

Question 3

You need to migrate a large on-premises PostgreSQL database to AlloyDB with minimal downtime. The database is 2 TB. Which migration strategy should you use?

Accepted Answer

Use Database Migration Service to migrate with continuous replication. Database Migration Service (DMS) supports continuous replication from PostgreSQL to AlloyDB, enabling minimal downtime migrations.

Answer

Use BigQuery Data Transfer Service

Answer

Export the database as SQL files and import into AlloyDB using pg_restore

Answer

Use gsutil to copy data files and restore

Question 4

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 practice of using multiple database technologies within a single application ecosystem, each chosen for its strengths.

Answer

Database replication

Answer

Multi-cloud database

Answer

Federated querying

Question 5

A company is deploying a microservices application on Google Cloud. They need a database for each service: one for user profiles (relational, high availability), one for product catalog (NoSQL, low latency), and one for session caching. Which THREE services should they use? (Select 3 answers)

Accepted Answer

Firestore. Cloud SQL for relational user profiles with HA, Firestore for NoSQL product catalog with low latency, Memorystore for session caching.

Answer

Cloud Spanner

Answer

Bigtable

Question 6

A company wants to migrate an on-premises MySQL database to Cloud SQL with minimal downtime. Which two steps should they take? (Choose two.)

Accepted Answer

Use Database Migration Service to create a continuous replication job. Database Migration Service (DMS) can be used for continuous replication. They also need to configure the source database for replication (binary logging). Cloud SQL proxy is for connecting applications, not migration.

Answer

Set up a Cloud SQL proxy on the source database

Answer

Take a full backup and restore it to Cloud SQL before replication

Answer

Disable foreign key checks on the source database

Question 7

A company is migrating a PostgreSQL database to AlloyDB using Database Migration Service. They want to ensure high availability during the migration with minimal risk. Which TWO practices should they follow? (Choose 2)

Accepted Answer

Set up DMS with continuous CDC to keep AlloyDB in sync. DMS supports continuous CDC, so you should enable CDC for minimal downtime. Testing with a clone avoids affecting production. Promoting the replica early would cause downtime.

Answer

Promote the replica immediately after the initial load

Answer

Disable binary logging on the source to improve performance

Answer

Use gcloud sql import command instead of DMS

Question 8

An e-commerce platform uses Cloud SQL for PostgreSQL. They need to reduce read load on the primary instance and provide low-latency reads for geographically distributed users. Which configuration should they implement?

Accepted Answer

Add read replicas in multiple regions. Cloud SQL read replicas are used to offload read traffic and provide low-latency reads from different regions. They are asynchronous replicas that can be promoted in case of failure.

Answer

Use Cloud CDN to cache database responses

Answer

Enable cross-region replication using Cloud SQL's built-in failover replica

Answer

Migrate to Cloud Spanner

Question 9

A mobile app needs to store user preferences and allow offline read-write sync when the device reconnects. The data is simple key-value pairs. Which Google Cloud database is MOST suitable?

Accepted Answer

Firestore. Firestore provides offline persistence and automatic sync, making it ideal for mobile apps. Cloud SQL does not have built-in offline sync. Bigtable is not designed for mobile clients. Memorystore is a cache, not a persistent database.

Answer

Memorystore for Redis

Answer

Cloud Bigtable

Answer

Cloud SQL

Question 10

A team is migrating a MySQL database to Cloud SQL for MySQL. They want to test the migration with a dual-write strategy before cutting over to the new database. Which TWO steps should they take?

Accepted Answer

Configure the application to write to both the source and target databases simultaneously.. Shadow writes (dual-write) involve writing to both databases and comparing results. Comparison queries and load testing are validation techniques.

Answer

Delete the source database after the first successful write.

Answer

Direct all reads to Cloud SQL to validate performance.

Answer

Use Database Migration Service to set up continuous replication.

Question 11

During a continuous migration job from on-premises MySQL to Cloud SQL, the engineer notices that the migration job fails after the full dump phase with an error about character set mismatch. The source uses utf8 charset, but Cloud SQL defaults to utf8mb4. What is the best action to resolve this?

Accepted Answer

Change the source database charset to utf8mb4. The source charset 'utf8' in MySQL is actually utf8mb3 (3-byte UTF-8). Cloud SQL MySQL 8.0 defaults to utf8mb4. To avoid data loss, the source tables should be converted to utf8mb4 before migration, or the target must be configured to accept utf8mb3 if compatible.

Answer

Ignore the error and promote the replica

Answer

Change Cloud SQL instance charset to utf8

Answer

Use a one-time migration instead

Question 12

An organization is migrating a large Oracle database to Cloud SQL for PostgreSQL. They need to handle Oracle's SEQUENCE objects, which are used for primary key generation. Which THREE approaches are valid for this migration?

Accepted Answer

Replace Oracle sequences with PostgreSQL SERIAL columns.. PostgreSQL has SERIAL, sequences, and IDENTITY columns. Oracle sequences can be converted to PostgreSQL sequences or IDENTITY columns. SERIAL is a shorthand for creating a sequence on a column.

Answer

Remove all sequences and use UUIDs generated by the application.

Answer

Use Oracle sequences directly in PostgreSQL via a compatibility layer.

Question 13

A company needs to back up their Cloud Bigtable instance for disaster recovery across regions. They want to restore to a different cluster in a different region. What should they use?

Accepted Answer

Use Bigtable managed backups and restore to a different cluster. Bigtable managed backups are cluster-level backups that can be restored to a different cluster, including cross-region, provided the restore is to an instance in the same project.

Answer

Export tables to Avro in GCS and import in another region

Answer

Use gcloud bigtable instances create with replication

Answer

Use Cloud Scheduler to copy tables via Dataflow

Question 14

A company needs to migrate an on-premises PostgreSQL database to Cloud SQL for PostgreSQL with near-zero downtime. Which TWO features of Database Migration Service (DMS) should they use?

Accepted Answer

Connection profiles. Continuous migration with CDC allows near-zero downtime by capturing ongoing changes after the initial dump. Connection profiles define source and target endpoints. A one-time dump would cause downtime. Continuous migration includes CDC.

Answer

Dataflow templates

Answer

Full dump only

Answer

One-time migration

Question 15

During a MySQL to Cloud SQL migration using DMS, the migration job completes the full dump and CDC phases, but the cutover step fails. The error says 'Source database write operations still occurring'. What should the engineer do to complete cutover?

Accepted Answer

Stop all write operations to the source database, then promote the Cloud SQL replica.. For a zero-downtime cutover, you must first stop writes to the source database, then promote the Cloud SQL replica. The error indicates writes are still happening; stopping them allows the CDC to catch up and then cutover.

Answer

Restart the DMS job from the beginning.

Answer

Manually apply remaining changes to Cloud SQL using a SQL script.

Answer

Increase the source database's binary log retention period.