PCDE Practice Exam 56 — 20 Questions

Question 1

You are migrating a relational database to Cloud Bigtable. The source schema has a Users table and an Orders table with a one-to-many relationship. The application frequently queries all orders for a user. Which three Bigtable schema design practices should you apply?

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

Accepted Answer

Denormalize by storing orders as multiple columns or a serialized column in the Users row. Cloud Bigtable is a wide-column NoSQL database that does not support joins. To efficiently query all orders for a user, you must denormalize the one-to-many relationship by storing orders as multiple columns (e.g., order_1, order_2) or as a serialized JSON/protobuf column within the user's row. This avoids the need for a separate lookup or join, enabling single-row reads for the user's orders.

Answer

Maintain 3NF to avoid data duplication

Answer

Keep the foreign key relationship by storing UserId in the Orders row key

Question 2

A company needs a fully managed, relational database with strong consistency and global distribution for a travel booking application that supports high concurrency and ACID transactions. Which Google Cloud database should they choose?

Accepted Answer

Cloud Spanner. Cloud Spanner is the correct choice because it is a fully managed, globally distributed relational database that provides strong consistency and ACID transactions across regions, making it ideal for high-concurrency travel booking applications that require global distribution and transactional integrity.

Answer

Cloud SQL

Answer

Cloud Bigtable

Answer

Firestore

Question 3

A startup is building a mobile application and needs a real-time database that automatically scales to handle sudden spikes in user traffic. They want to minimise operational overhead and only pay for the resources they use. Which Google Cloud database should they choose?

Accepted Answer

Firestore. Firestore is a fully managed, serverless NoSQL document database that automatically scales horizontally to handle sudden traffic spikes without manual intervention. It offers real-time data synchronization via listeners, and its pay-per-use billing model aligns with the startup's requirement to minimize operational overhead and only pay for consumed resources.

Answer

Cloud Spanner

Answer

Cloud SQL

Answer

Cloud Bigtable

Question 4

A company is migrating a monolithic application to a microservices architecture and plans to use multiple Google Cloud databases. The application has the following workloads: (1) user profiles with high read/write concurrency, (2) product catalog with complex queries, (3) session data that requires low-latency access. Which three Google Cloud databases should be used? (Choose three.)

Accepted Answer

Firestore. Cloud SQL is correct for the product catalog with complex queries because it is a fully managed relational database that supports standard SQL, enabling complex joins and aggregations. Firestore is correct for user profiles with high read/write concurrency because it is a NoSQL document database that scales horizontally and provides strong consistency. Memorystore (Redis) is correct for session data requiring low-latency access because it is an in-memory cache delivering sub-millisecond response times. Cloud Bigtable is designed for high-throughput time-series or key-value data, not complex queries, and Cloud Spanner is more suited for globally distributed transactional workloads.

Answer

Cloud Bigtable

Answer

Cloud Spanner

Question 5

An SRE team is creating a postmortem after a service outage. They want to ensure the process is blameless and focuses on systemic improvements. Which practice is central to a blameless postmortem?

Accepted Answer

Assigning action items with owners and due dates to prevent recurrence. A blameless postmortem focuses on identifying contributing factors and systemic issues rather than assigning blame to individuals. The 5 Whys technique helps drill down to root causes.

Answer

Determining the financial cost of the outage

Answer

Escalating the issue to senior management

Answer

Identifying the individual who caused the incident for performance review

Question 6

A Cloud SQL for PostgreSQL instance is running low on disk space. The database size is 500 GB and the current storage is 600 GB. The engineer needs to increase storage to 800 GB without downtime. What should they do?

Accepted Answer

Use gcloud sql instances patch to increase storage size to 800 GB.. Cloud SQL for PostgreSQL supports online storage increases using the `gcloud sql instances patch` command, which resizes the disk without requiring an instance restart or downtime. The storage can be increased up to the maximum allowed for the instance tier, and the change takes effect immediately while the instance remains available.

Answer

Shut down the instance, edit the configuration to increase storage, then restart.

Answer

Create a new instance with 800 GB storage and migrate data using pg_dump.

Answer

Enable auto-storage increase and wait for it to happen automatically.

Question 7

A game development company wants to use Memorystore for Redis as a session store. They need to ensure that when memory is full, the least recently used keys are evicted first. Which eviction policy should they configure?

Accepted Answer

allkeys-lru. (allkeys-lru) is correct because the requirement is to evict the least recently used keys from the entire keyspace when memory is full. The 'allkeys-lru' policy applies the LRU algorithm to all keys, regardless of whether they have an expiry set, which matches the need to evict the least recently used keys first across the entire dataset.

Answer

volatile-lru

Answer

volatile-ttl

Answer

noeviction

Question 8

A company uses Cloud SQL for PostgreSQL and wants to create a cross-region read replica for disaster recovery (DR) purposes. They also want the option to promote the replica to a standalone instance in the event of a regional outage. What should the engineer do?

Accepted Answer

Create a cross-region read replica and use gcloud sql instances promote-replica to promote it during DR.. Cloud SQL for PostgreSQL supports cross-region read replicas, which can be promoted to standalone instances using the `gcloud sql instances promote-replica` command. This provides a managed DR solution with minimal data loss (asynchronous replication) and faster failover compared to export/import or backup restore methods.

Answer

Export the database as a SQL file and import it into a new instance in the target region during DR.

Answer

Create a same-region read replica and enable point-in-time recovery on it.

Answer

Configure cross-region backup replicas and restore from backup in the target region.

Question 9

A company is migrating CI/CD pipelines to Google Cloud. They want to deploy containerized applications to GKE using GitOps principles with Config Sync. Which two components are required? (Choose 2)

Accepted Answer

Config Sync operator (reconciler) installed on the GKE cluster. Config Sync requires a Git repository as the source of truth (source of truth) and the Config Sync operator installed on the cluster to sync. Cloud Build is not required for Config Sync itself.

Answer

Artifact Registry

Answer

Cloud Build trigger

Answer

Binary Authorization

Question 10

A company is migrating Oracle to Cloud SQL for PostgreSQL using Ora2Pg. For a column defined as NUMBER(10,2) in Oracle, what is the corresponding data type in PostgreSQL?

Accepted Answer

NUMERIC(10,2). Oracle's NUMBER(10,2) specifies a fixed-point number with up to 10 digits total and 2 digits after the decimal point. PostgreSQL's NUMERIC(10,2) is the direct equivalent, offering identical precision and scale semantics. Ora2Pg automatically maps NUMBER(p,s) to NUMERIC(p,s) to preserve exact numeric storage.

Answer

INTEGER

Answer

DOUBLE PRECISION

Answer

TEXT

Question 11

A developer needs to connect to a Memorystore for Redis instance from a Compute Engine VM in the same VPC network. The Redis instance has AUTH enabled. What must the developer provide in the connection string?

Accepted Answer

The Redis AUTH password.. When AUTH is enabled on a Memorystore for Redis instance, the client must provide the AUTH password in the connection string (e.g., `redis://:password@host:6379`) or via the `AUTH` command after connecting. This password is set during instance creation and is required for authentication before any data commands can be executed. Without it, the Redis server will reject the connection with a `NOAUTH Authentication required` error.

Answer

The IAM role 'Memorystore User'.

Answer

The client certificate and private key.

Answer

The service account key file.

Question 12

You have a Cloud Bigtable instance with a single cluster. To improve availability and durability, you want to enable replication across two regions. After configuring replication, you notice that reads from the replica cluster show data that is not yet consistent with the primary. What is the expected consistency model for Bigtable replication?

Accepted Answer

Eventually consistent reads from replicas. Cloud Bigtable replication uses an eventually consistent model for reads from replica clusters. When you write to the primary cluster, the data is asynchronously replicated to the replica cluster using a distributed replication pipeline. This means that reads from the replica cluster may return stale data until the replication process completes, and there is no guarantee of immediate consistency with the primary.

Answer

Read-your-writes consistency from the primary

Answer

Strongly consistent reads from any cluster

Answer

Strict serializability across clusters

Question 13

A Cloud Memorystore for Redis instance is running out of memory. The team wants to automatically remove the least recently used keys when memory is full. Which eviction policy should they configure?

Accepted Answer

allkeys-lru. The `allkeys-lru` eviction policy is correct because it applies the LRU (Least Recently Used) algorithm to all keys in the Redis instance, not just those with an expiry set. This ensures that when memory is full, the least recently accessed keys are automatically removed, regardless of whether they have a TTL, which directly meets the requirement to free memory without manual intervention.

Answer

volatile-lru

Answer

volatile-ttl

Answer

noeviction

Question 14

You are using Cloud Monitoring to track performance of a Cloud Spanner instance. Which metric indicates that a database is approaching its throughput limits and may need a split or additional nodes?

Accepted Answer

High CPU utilization (percentage). High CPU utilization (percentage) is the correct metric because Cloud Spanner's CPU utilization directly reflects the processing load on the instance's nodes. When CPU utilization consistently exceeds 65-70%, it indicates the database is approaching its throughput limits, often requiring a split (to distribute load across more tablets) or additional nodes to maintain performance and avoid throttling.

Answer

Storage utilization (bytes used)

Answer

Query error rate (errors per second)

Answer

Average commit latency

Question 15

A team is designing a BigQuery schema for time-series analytics on IoT sensor data. They expect high write throughput and queries that aggregate data by hour. Which partitioning and clustering strategy is most cost-effective?

Accepted Answer

Partition by date and cluster by sensor_id with a timestamp column.. Partitioning by date (e.g., _PARTITIONDATE) allows BigQuery to prune partitions when querying hourly aggregates, drastically reducing scanned bytes. Clustering by sensor_id with a timestamp column further organizes data within each partition, enabling efficient filtering and sorting for sensor-specific queries. This combination optimizes both write throughput (partitioning avoids small, frequent partitions) and query performance (clustering reduces scan on sensor_id filters).

Answer

Partition by ingestion_time and cluster by sensor_id.

Answer

Use integer range partitioning on sensor_id.

Answer

Partition by sensor_id and cluster by timestamp.

Question 16

A company is migrating a PostgreSQL database to Cloud SQL using DMS. The source database has logical replication enabled for the migration. What is the purpose of logical replication in this context?

Accepted Answer

To capture changes for continuous replication after the initial dump.. DMS uses PostgreSQL logical replication to capture ongoing changes. The source database must have logical replication enabled (via WAL with logical decoding) to allow DMS to replicate changes continuously after the initial dump. Binary logging is a MySQL concept, not applicable to PostgreSQL.

Answer

To enable point-in-time recovery on the source.

Answer

To improve performance of the initial dump.

Answer

To convert data types between source and destination.

Question 17

A Cloud Bigtable cluster is currently using HDD storage. The team wants to switch to SSD for better performance. What is the correct approach?

Accepted Answer

Create a new cluster in the same instance with SSD, then delete the old HDD cluster.. In Cloud Bigtable, storage type is a property of the cluster, not the instance. You cannot change the storage type of an existing cluster. The correct approach is to add a new cluster with SSD storage to the same instance, then delete the original HDD cluster. This allows you to migrate without data loss or downtime, as data is replicated across clusters in the same instance.

Answer

Use the gcloud bigtable clusters update command with the --storage-type flag.

Answer

Export the table to Cloud Storage, delete the instance, create a new one with SSD, and import.

Answer

Delete the existing cluster and recreate it with SSD. Data is retained in the instance.

Question 18

A company is deploying a microservice on Cloud Run that needs to handle up to 1000 concurrent requests per instance. The default concurrency setting is 80. How should they configure the service to achieve the desired concurrency?

Accepted Answer

Set the `--concurrency` flag to 1000.. Cloud Run allows setting max concurrent requests per instance via the `--concurrency` flag. Setting it to 1000 enables the desired throughput.

Answer

Set the `--execution-environment` to gen2.

Answer

Set the `--cpu` flag to 4.

Answer

Set the `--max-instances` flag to 1000.

Question 19

A Cloud Spanner database has a parent table 'Customers' and a child table 'Orders' interleaved on CustomerId. The most common query retrieves the last 10 orders for a given customer. How should the primary key of Orders be defined for optimal performance?

Accepted Answer

(CustomerId, OrderDate DESC). Defining the primary key as (CustomerId, OrderDate DESC) leverages Cloud Spanner's interleaved table structure to physically co-locate rows for the same customer, and the descending order on OrderDate allows the most common query (retrieving the last 10 orders) to be served as a sequential scan of the most recent rows without sorting or a full table scan.

Answer

(CustomerId, OrderId)

Answer

Add a commit timestamp column as part of the primary key

Answer

No change; use a secondary index on OrderDate

Question 20

A company is running a Cloud SQL for PostgreSQL database and wants to improve read performance for reporting queries. They have already optimized the queries but still see high CPU usage on the primary instance. What is the most cost-effective solution?

Accepted Answer

Add a read replica and direct reporting traffic to it.. Read replicas offload read traffic from the primary instance, reducing CPU usage without requiring a larger primary instance.

Answer

Enable connection pooling with PgBouncer on the primary.

Answer

Increase the memory of the primary instance.

Answer

Create a Cloud SQL Auth Proxy and use it for all connections.