PCDE Practice Exam 68 — 20 Questions

Question 1

A company is migrating a large on-premise Hadoop workload to Google Cloud. The data is stored in HBase and consists of time-series logs with 10 PB of data. They need a fully managed NoSQL solution with high throughput and low latency. Which migration path should they choose?

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

Accepted Answer

Use Cloud Bigtable and the HBase client. Cloud Bigtable is the fully managed, scalable NoSQL database that is compatible with HBase API, making migration straightforward. Cloud Spanner is relational, not the best for time-series logs. BigQuery is for analytics, not real-time. Firestore is document-based and not suited for petabyte-scale logs.

Answer

Migrate HBase tables to Cloud Spanner using Dataflow

Answer

Export data to BigQuery using Storage Transfer Service

Answer

Re-architect as Firestore collections

Question 2

You are designing a schema for Cloud Spanner and need to avoid write hotspots. Which primary key design strategy is recommended?

Accepted Answer

Use a UUID or hash prefix as the first part of the primary key. Using a UUID or a hash prefix as the first part of the primary key ensures that writes are distributed across nodes, avoiding hotspots. Monotonically increasing keys like timestamps cause all writes to hit the same tablet, creating a hotspot.

Answer

Use the most frequently queried column as the primary key

Answer

Use a composite key with the leading column being a timestamp

Answer

Use a monotonically increasing timestamp as the primary key

Question 3

A company is migrating an on-premises OLTP application to Google Cloud. The application requires high concurrency (up to 5,000 simultaneous connections) and uses a relational schema with strong transactional integrity. Which database service is the MOST suitable?

Accepted Answer

Cloud SQL. Cloud SQL supports up to 4,096 connections by default (configurable) and provides full transactional integrity. For 5,000 connections, Cloud SQL can be configured with appropriate instance sizing. Spanner also supports transactions but is overkill for a single-region OLTP migration. BigQuery is for analytics, Firestore is NoSQL.

Answer

Firestore

Answer

BigQuery

Answer

Cloud Spanner

Question 4

A company is building a real-time leaderboard for a mobile game using Google Cloud. The data includes player scores that update frequently (thousands of writes per second) and queries for top 100 players. Which database is most suitable?

Accepted Answer

Cloud Bigtable. Cloud Bigtable is a good fit for high write throughput and simple range scans (e.g., scanning top scores). Firestore has limited write capacity. Cloud SQL cannot handle thousands of writes per second. Spanner can but is overkill and more expensive.

Answer

BigQuery

Answer

Cloud Firestore

Answer

Cloud SQL (PostgreSQL)

Question 5

A team is designing a Spanner schema for an online gaming leaderboard. The leaderboard stores player scores and requires high write throughput. Which primary key design is BEST to avoid write hotspots?

Accepted Answer

Primary key: (HashOfPlayerId, Timestamp). Monotonically increasing keys (like score or timestamp) cause hotspotting. Using a random prefix (e.g., hash of player ID) ensures writes are distributed across splits. Player ID alone might also cause hotspotting if many players write simultaneously.

Answer

Primary key: (PlayerId, Timestamp)

Answer

Primary key: (Score, PlayerId)

Answer

Primary key: (Timestamp, PlayerId)

Question 6

A company is designing a Cloud Spanner database for a global financial application. They need to minimize latency for customer queries while handling write-heavy workloads. The current design uses a single-region instance in us-central1. Which approach should they take to reduce latency for users in Europe?

Accepted Answer

Reconfigure the instance to a multi-region configuration with default leader in europe-west1.. To reduce latency for users in Europe, the database must have a write-capable replica close to them. A multi-region configuration with the default leader in europe-west1 ensures that writes are committed in Europe, minimizing write latency for European users. Read-only replicas (Option C) cannot handle writes, so they do not reduce write latency.

Answer

Reconfigure the instance to a multi-region configuration with default leader in us-central1.

Answer

Add a read-only regional replica in europe-west1.

Answer

Increase the number of nodes to improve throughput and automatically reduce latency.

Question 7

A company wants to set up error budget alerting in Cloud Monitoring for a service with a 99.9% SLO over 30 days. They want to receive alerts when the error budget burn rate reaches certain thresholds. Which TWO of the following are typical recommendations for alerting thresholds?

Accepted Answer

14x burn rate over 1 hour. Common SRE practice uses a fast burn alert (e.g., 14x burn rate over 1 hour) and a slow burn alert (e.g., 5x burn rate over 6 hours) to cover both rapid and gradual budget consumption.

Answer

100x burn rate over 1 minute

Answer

2x burn rate over 1 day

Answer

1x burn rate over 30 days

Question 8

A Cloud Spanner instance has a single node and is experiencing high write contention. The workload is 3000 writes per second with 2 KB mutations. Which two changes would improve write throughput? (Choose TWO.)

Accepted Answer

Redesign the primary key to distribute writes evenly across splits.. High write contention in Cloud Spanner often stems from hotspotting, where all writes target the same split. By redesigning the primary key to distribute writes evenly across splits, you reduce contention and improve throughput. This is a fundamental design pattern for Spanner's distributed architecture.

Answer

Increase the mutation size to 10 KB to reduce number of writes.

Answer

Use a monotonically increasing primary key to improve index performance.

Answer

Split the table into multiple smaller tables.

Question 9

Your Firestore database in Native mode contains a collection with millions of documents. You need to query documents where the 'tags' field (an array) contains the string 'urgent'. What must you ensure in your index configuration?

Accepted Answer

No additional index configuration is required; Firestore automatically creates the necessary index for array fields.. Firestore automatically creates a single-field index for array fields. However, to query array-contains, you need an index on the field with the array-contains filter. Firestore automatically creates a single-field index for the 'tags' field, so no additional index is needed. If the query includes additional equality clauses, a composite index may be required, but for a simple array-contains, it's automatic.

Answer

Ensure the 'tags' field is not indexed, and then create a composite index with the array-contains filter.

Answer

Create an index exemption for the 'tags' field to enable array queries.

Answer

Create a composite index on 'tags' and '__name__' for the collection.

Question 10

Refer to the exhibit. A BI query is performing slowly. The query plan shows a large shuffle in the aggregate stage. The table is not partitioned or clustered. Which optimization would most directly reduce the shuffle size?

Accepted Answer

Clustering the table on the grouping columns.. Clustering the table on the grouping columns physically co-locates rows with the same group key values within the same storage units (e.g., files or partitions). This allows the query engine to perform partial aggregation locally before the shuffle, dramatically reducing the amount of data that must be moved across the network during the aggregate stage. In systems like BigQuery or Spark SQL, clustering on grouping columns directly minimizes shuffle size by enabling pre-aggregation at the storage layer.

Answer

Converting the query to use a window function.

Answer

Using a materialized view.

Answer

Adding a WHERE clause to filter recent data.

Question 11

You need to monitor the replication lag between a Cloud SQL for MySQL primary instance and its read replica. Which metric should you use to set up an alert?

Accepted Answer

cloudsql.googleapis.com/database/replication/replication_lag. Cloud SQL exposes a metric 'replication/replication_lag' (or 'cloudsql.googleapis.com/database/replication/replication_lag') that measures the lag in seconds between the primary and replica. This is the correct metric for alerting.

Answer

cloudsql.googleapis.com/database/replication/replica_count

Answer

cloudsql.googleapis.com/database/cpu/utilization

Answer

cloudsql.googleapis.com/database/memory/utilization

Question 12

You manage a Memorystore for Redis instance that is regularly hitting its maximum memory limit. The application can tolerate some data loss and prefers to keep the most recently used data. Which eviction policy should you configure?

Accepted Answer

volatile-lru. volatile-lru evicts keys with an expiry set (volatile keys) using an LRU (least recently used) algorithm. This fits the requirement: the application can tolerate loss of expired data, and it prefers to keep recently used data. allkeys-lru would evict any key, which might include important unexpired keys.

Answer

noeviction

Answer

volatile-ttl

Answer

allkeys-lru

Question 13

A company has a Cloud SQL for PostgreSQL instance and wants to enable point-in-time recovery (PITR) with a recovery window of 5 days. Which configuration step is required?

Accepted Answer

Enable automated backups and set backup retention to 5 days. PITR in Cloud SQL for PostgreSQL uses Write-Ahead Logging (WAL) archives. You must enable automated backups and set the backup retention to the desired recovery window (1-7 days). Binary logging is for MySQL, not PostgreSQL. Cloud Storage archiving is separate. WAL archiving is automatically managed when automated backups are enabled with a retention period.

Answer

Enable binary logging on the instance

Answer

Configure a Cloud Storage bucket for WAL archiving

Answer

Create a cross-region backup replica for disaster recovery

Question 14

A Cloud SQL for PostgreSQL instance is experiencing high read traffic. You need to offload read queries and ensure the solution can survive a regional outage. What should you do?

Accepted Answer

Create a cross-region read replica and direct read traffic to it.. Cross-region read replicas serve read traffic and provide disaster recovery if the primary fails. Creating a cross-region read replica reduces read load and can be promoted if the primary region fails. Option D is correct. Option A (Cloud Memorystore cache) reduces latency but does not survive a regional outage. Option B (increasing machine type) helps performance but not regional failover. Option C (same-region read replica) does not survive a regional outage.

Answer

Set up Cloud Memorystore as a cache in front of the database.

Answer

Increase the machine type of the primary instance to handle the load.

Answer

Create a read replica in the same region and use it for read queries.

Question 15

A company uses Firestore in Native mode. They have a collection with 1 million documents and frequently run queries that filter on two fields: status and createdAt. The queries are slow. What should the team do?

Accepted Answer

Create a composite index on (status, createdAt). Firestore creates single-field indexes automatically but for multi-field queries, a composite index must be created manually. Without it, queries may be slow or fail.

Answer

Create an index exemption for the status field

Answer

Use the Datastore mode instead

Answer

Add an index exemption for the createdAt field

Question 16

A large enterprise uses Cloud Bigtable for analytics. They notice that some nodes are handling significantly more traffic than others, causing hot spots and performance degradation. Which tool should they use to identify the specific row keys causing the issue?

Accepted Answer

Bigtable Key Visualiser. Key Visualiser is a Bigtable tool that provides a heatmap of row key access patterns, helping to identify hot spots by showing which row key ranges are heavily accessed.

Answer

Stackdriver Error Reporting

Answer

Bigtable cbt tool with read rows command

Answer

Cloud Monitoring dashboard for Bigtable

Question 17

A company is migrating their on-premises Oracle database to Cloud SQL for PostgreSQL. They want to test the converted stored procedures using unit tests. Which framework should they use?

Accepted Answer

pgTAP. pgTAP is a unit testing framework for PostgreSQL that can test stored procedures and functions.

Answer

pgAdmin

Answer

SQL Developer

Answer

Ora2Pg

Question 18

An organization is migrating a large on-premises MySQL database to Cloud SQL using DMS. They want to minimize downtime. Which TWO configurations should they implement? (Choose 2)

Accepted Answer

Enable continuous migration with CDC.. Continuous migration enables CDC. Parallel dump speeds up the initial sync.

Answer

Disable binary logging on the source.

Answer

Use a one-time migration job.

Answer

Use mysqldump and import manually.

Question 19

A company uses AlloyDB for an e-commerce platform. They want to achieve the highest availability within a single region. What configuration should they use, and what is the expected failover RTO?

Accepted Answer

Use a primary instance with a standby in a different zone in the same region; RTO less than 30 seconds. AlloyDB offers an HA configuration with a primary instance and a standby (read pool) in different zones within the same region. Automatic failover occurs in less than 30 seconds. Cross-zone failover is automatic. There is no cross-region HA in AlloyDB (you can use cross-region replicas but that requires manual promotion).

Answer

Use a primary instance with a standby in the same zone; RTO less than 10 seconds

Answer

Use a primary instance with multiple read pools; RTO less than 5 seconds

Answer

Use a primary instance with a cross-region read replica; RTO less than 1 minute

Question 20

A company needs to define backup retention policies for Cloud SQL, Spanner, and Bigtable to meet compliance requirements. Which THREE statements about backup retention are correct? (Choose three.)

Accepted Answer

Cloud SQL automated backups can be retained for up to 365 days.. Cloud SQL automated backups can be retained for up to 365 days. Spanner backup expiration is maximum 365 days. Bigtable on-demand backups are stored in Cloud Storage and can be retained indefinitely using lifecycle policies. The other options are incorrect: Cloud SQL maximum is 365 days, Spanner maximum is 365 days, Bigtable backups are not limited to 30 days.

Answer

Cloud SQL automated backups can be retained for up to 730 days.

Answer

Bigtable managed backups have a maximum retention of 30 days.