PCD Design Scalable and Highly Available Cloud Database Solutions Practice Test 11 — 15 Questions

Question 1

A financial services company needs a globally distributed database with strong consistency across continents, 99.999% SLA, and support for ACID transactions. They expect millions of transactions per day. Which Google Cloud database should they use?

Accepted Answer

Cloud Spanner. Cloud Spanner is the only Google Cloud database that offers global distribution with strong consistency, ACID transactions, and 99.999% SLA. It is designed for mission-critical workloads that require horizontal scaling and geo-replication.

Answer

Cloud SQL

Answer

Bigtable

Answer

Firestore

Question 2

A retail company needs a scalable NoSQL database for a mobile app with offline synchronization, real-time updates, and flexible security rules. The data model is document-based. Which Google Cloud service should they choose?

Accepted Answer

Firestore. Firestore is a fully managed, serverless NoSQL document database that provides offline support, real-time listeners, and security rules for mobile and web apps.

Answer

Memorystore for Redis

Answer

Cloud SQL

Answer

Cloud Bigtable

Question 3

Which of the following is NOT a valid use case for Cloud Bigtable?

Accepted Answer

Serving as a transaction processing database for an e-commerce website. Cloud Bigtable is a NoSQL, wide-column database optimized for high-throughput, low-latency analytical and operational workloads, but it does not support multi-row transactions or ACID guarantees. Therefore, it is not suitable as a transaction processing database for an e-commerce website, which requires strong consistency and transactional integrity for order management and inventory updates.

Answer

Analyzing ad-tech clickstream data

Answer

Storing time-series data from IoT sensors

Answer

Powering a financial market data feed with millisecond latency

Question 4

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 5

A DevOps engineer is designing a row key for a Bigtable table storing user activity logs. The pattern is: user_id (UUID) + timestamp. On a cluster with 10 nodes, they observe severe hotspotting on a single node during peak writes. Which row key design change would likely resolve this issue?

Accepted Answer

Use a hash of the user_id as the prefix. Option A is correct because prepending a hash of the user_id distributes writes uniformly across all Bigtable tablets. Bigtable uses the row key prefix to determine tablet assignment; a UUID prefix is random but sequential UUIDs (e.g., time-based) can cluster writes. A hash function (e.g., MD5 or CRC32) ensures even distribution, eliminating hotspotting on a single node.

Answer

Use a single table with no row key change

Answer

Increase the number of nodes to 20

Question 6

Which Google Cloud database service provides a fully managed, in-memory caching solution compatible with the Redis protocol?

Accepted Answer

Memorystore for Redis. Memorystore for Redis provides a managed Redis service for caching, session stores, and pub/sub messaging.

Answer

Firestore

Answer

Bigtable

Answer

Cloud SQL

Question 7

A company is migrating an on-premises PostgreSQL database to Google Cloud. They need high availability with automatic failover and zero RPO. Which Cloud SQL configuration should they choose?

Accepted Answer

Cloud SQL HA instance (regional). Cloud SQL HA instances use synchronous replication to a standby in the same region, providing automatic failover and zero RPO.

Answer

Cloud SQL with cross-region replication

Answer

Cloud SQL read replica in a different region

Answer

Single zone Cloud SQL instance with automated backups

Question 8

A gaming company uses Cloud Spanner for their global leaderboard. They want to reduce the number of stale reads and improve read performance while maintaining strong consistency for writes. Which TWO strategies should they implement? (Choose two)

Accepted Answer

Create secondary indexes on frequently queried columns. Option C is correct because secondary indexes in Cloud Spanner allow queries to access data directly from the index without scanning the entire base table, significantly improving read performance for frequently queried columns. Option E is correct because stale reads with a maximum staleness bound reduce contention and latency by allowing reads to return data that is slightly behind the current timestamp, which improves read throughput while still maintaining strong consistency for writes.

Answer

Use interleaved tables to store child rows with parent rows

Answer

Increase the number of read replicas in each region

Answer

Use strong reads for all queries

Question 9

A data engineer is designing a Bigtable schema for a global ad-tech platform. The workload includes time-series clickstream data with row keys like 'advertiser_id#campaign_id#timestamp'. They are experiencing uneven load distribution. Which TWO row key design changes would best distribute writes across nodes? (Choose two)

Accepted Answer

Swap the order to 'timestamp#advertiser_id#campaign_id'. Option A is correct because placing the timestamp first in the row key ensures that writes are spread across the Bigtable tablet server range. In Bigtable, rows are sorted lexicographically by row key; leading with a monotonically increasing value (like timestamp) causes all new writes to hit a single tablet, creating a hotspot. By swapping to 'timestamp#advertiser_id#campaign_id', writes are still sequential but the timestamp prefix alone does not guarantee perfect distribution—however, combined with salting (Option E), it avoids the original hotspot caused by the advertiser_id prefix.

Answer

Use a single table per advertiser

Answer

Increase the number of Bigtable nodes to 100

Answer

Use a composite key with campaign_id first

Question 10

A startup is building a mobile app with user-generated content (text and images). They need a database that provides offline support, real-time synchronization, and flexible security rules. Which TWO Google Cloud services should they consider? (Choose two)

Accepted Answer

Firestore. Firestore provides offline sync and real-time updates. Cloud Storage can store images and other large files with security rules. Cloud SQL and Bigtable are not suited for mobile offline sync.

Answer

Cloud SQL

Answer

Bigtable

Answer

Cloud Spanner

Question 11

A company is using Cloud Spanner for a global inventory system. They need to ensure that queries for an order and its line items are fast. Which THREE design choices will help achieve this? (Choose three)

Accepted Answer

Use interleaved tables for orders and line items. Interleaved tables in Cloud Spanner physically co-locate parent and child rows on the same split, so a query joining orders and line items by the parent key (order_id) can be served from a single split without distributed reads. This eliminates cross-node network hops, dramatically reducing latency for the inventory system's order+line-item queries.

Answer

Store orders and line items in separate regions

Answer

Use global secondary indexes on line items

Question 12

A healthcare company uses Cloud SQL for PostgreSQL to store patient records. They need to implement a disaster recovery plan with cross-region failover capability and minimal data loss. Which TWO steps should they take? (Choose two)

Accepted Answer

Enable automated backups and point-in-time recovery. Cross-region read replicas can be promoted in a disaster, but they may have data loss. To minimize loss, use Cloud SQL HA in the primary region plus a cross-region read replica. Automated backups provide point-in-time recovery but not automatic failover.

Answer

Migrate to Cloud Spanner for multi-region support

Answer

Use Cloud SQL HA instance in the primary region

Answer

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

Question 13

A company needs to run HTAP (hybrid transactional/analytical processing) workloads on PostgreSQL. They require 4x faster OLTP performance than standard PostgreSQL and the ability to run analytical queries directly on transactional data without ETL. Which TWO Google Cloud databases should they consider? (Choose two)

Accepted Answer

AlloyDB with BigQuery Omni. AlloyDB is designed for HTAP, with a columnar engine for fast analytics and 4x faster OLTP. Cloud SQL is not optimized for analytics. BigQuery is for analytics but not transactional. Spanner is globally distributed but not specifically for HTAP.

Answer

Cloud Spanner

Answer

Cloud SQL for PostgreSQL

Answer

BigQuery

Question 14

A developer is using Firestore in Native mode for a mobile app. They want to secure data access based on user authentication. Which TWO mechanisms should they use? (Choose two)

Accepted Answer

Firestore Security Rules. Firestore Security Rules allow granular access control. Firebase Authentication integrates with Firestore for user identity. IAM roles are for project-level access, not per-document. Cloud Armor is for network security. SSL/TLS is always enabled.

Answer

Cloud Armor

Answer

SSL/TLS encryption in transit

Answer

Cloud Identity and Access Management (IAM) roles

Question 15

A company runs a global e-commerce site on Cloud Spanner. They notice that some queries on the Orders table by customer_id are slow because customer_id is not part of the primary key (order_id). They want to avoid full table scans. Which TWO actions will improve query performance? (Choose two)

Accepted Answer

Create a secondary index on customer_id. A secondary index on customer_id will speed up queries. The STORING clause can include additional columns to avoid index joins. A global index is needed because customer_id is not in the primary key. Interleaving would require a specific parent-child relationship.

Answer

Increase the number of nodes to improve scan speed

Answer

Re-create the table with customer_id as the first part of the primary key

Answer

Use interleaved tables to store customer data with orders