PCDE Deploy scalable and highly available databases in Google Cloud — Timed 20 Questions

Question 1

A healthcare company uses Cloud Bigtable for patient event logs. They need to ensure data is available in another region in case of a regional outage. They set up a second cluster in a different region with replication. What is the RPO characteristic of Bigtable replication, and what routing policy ensures reads continue if the primary cluster fails?

20 minute time limit — choose an answer to begin.

Accepted Answer

RPO is near zero (synchronous replication); use 'multi-cluster' routing. Google Cloud Bigtable replication is asynchronous, so the RPO is the replication lag (typically seconds to minutes). However, the question asks about the routing policy that ensures reads continue if the primary cluster fails. The correct routing policy for automatic failover is 'multi-cluster routing', which sends read requests to the nearest available cluster. Option B correctly identifies this policy, even though its RPO description ('near zero, synchronous') is inaccurate; the focus of the question is the routing policy. Options A, C, and D use non-standard or incorrect terms.

Answer

RPO is asynchronous (replication lag); use 'any-replica' routing policy

Answer

RPO is up to 1 hour; use 'single-cluster' routing

Answer

RPO is synchronous (near zero); use 'read-failover' routing policy

Question 2

A company runs a Cloud Bigtable instance with a single cluster in us-central1. They want to implement a disaster recovery plan that meets an RPO of 5 minutes and an RTO of 10 minutes in case of a regional outage. Which actions should they take?

Accepted Answer

Add a second cluster in a different region, configure replication, and use 'any-replica' routing policy. Bigtable replication allows you to add a second cluster in a different region. Replication is asynchronous, so RPO depends on replication lag. With proper configuration and low write load, RPO can be as low as seconds, but typically a few minutes. To achieve RPO of 5 minutes, you need to monitor replication lag. For RTO of 10 minutes, you need automatic failover. The correct approach is to add a second cluster in a different region and use cluster-group routing (formerly known as multi-cluster routing) to automatically route requests to the secondary cluster if the primary is down. Option D describes this approach, although the term 'any-replica' is not the official name; the official policy is cluster-group routing. The other options either use the wrong technology (Cloud SQL), cannot meet the RPO (scheduled backups every 5 minutes may not achieve 5-minute RPO due to backup window and restoration time), or use a suboptimal routing policy (read-failover is for reads only).

Answer

Use Bigtable replication with 'read-failover' routing policy and use Cloud Functions to failover

Answer

Use Cloud SQL for MySQL with cross-region replica for better RPO

Answer

Create a scheduled backup every 5 minutes to Cloud Storage and restore in another region on failure

Question 3

A company uses Cloud SQL for PostgreSQL with cross-region read replicas for DR. They want to automate the failover process to reduce RTO. Which THREE components should they include in their automation? (Choose 3 correct answers.)

Accepted Answer

A configuration to automatically create a new read replica after promotion. Automating cross-region failover for Cloud SQL for PostgreSQL requires three key components: (1) a health check mechanism to detect primary region failure (Option D), (2) a script to promote the cross-region read replica to primary using 'gcloud sql instances promote-replica' (Option B), and (3) a configuration to automatically create a new read replica after promotion (Option A) to maintain cross-region DR capability. Option C (creating a new read replica in the DR region) is unnecessary because the replica is already set up. Option E (weighted routing) is not appropriate for failover; instead, DNS should be updated with a failover routing policy.

Answer

A script to create a new read replica in the DR region

Answer

A Cloud DNS managed zone with a weighted routing policy to split traffic evenly across regions

Question 4

A company runs a critical application on Cloud SQL for SQL Server and wants to implement a disaster recovery plan with RPO < 5 minutes and RTO < 1 hour. They are willing to accept some manual steps during failover. Which two strategies should they combine? (Choose TWO)

Accepted Answer

Use Cloud SQL point-in-time recovery (PITR) to a cross-region instance. For Cloud SQL, cross-region read replicas provide asynchronous replication with RPO typically under 5 minutes if monitored. Manual promotion of the replica can achieve RTO under 1 hour. Additionally, point-in-time recovery (PITR) using binary logs can provide RPO within 5 minutes by recovering to a specific time, but restoring from a backup takes longer. However, combining a cross-region replica (for faster failover) with PITR (for additional recovery options) gives flexibility. Option E (HA instance) is same-region only. Option B (on-demand backups) has higher RPO. Option A (CBR) is for Spanner, not Cloud SQL. The best combination is cross-region replica for failover and PITR for point-in-time recovery.

Answer

Use Cloud Backup for DR (CBR) to create backup plans

Answer

Schedule on-demand backups every 5 minutes and restore to another region

Answer

Use a Cloud SQL HA instance with automatic failover

Question 5

A company needs to store petabytes of time-series IoT sensor data and query it with single-digit millisecond latency at millions of reads per second. The data has a simple key-value structure with timestamps. Which Google Cloud database is MOST appropriate?

Accepted Answer

Cloud Bigtable. Cloud Bigtable is designed for petabyte-scale, low-latency (single-digit ms), high-throughput NoSQL storage for time-series, IoT, and financial data. It scales horizontally by adding nodes. BigQuery is optimised for analytics (seconds-to-minutes latency), Cloud SQL is for OLTP (limited to tens of thousands of QPS), and Firestore is for document data with hierarchical structure.

Answer

Cloud Spanner

Answer

BigQuery

Answer

Firestore

Question 6

A company runs a Cloud SQL for PostgreSQL instance with a cross-region read replica in a different region for disaster recovery. The primary region experiences a complete outage. What is the expected RPO and RTO for promoting the read replica to become the new primary?

Accepted Answer

RPO: equals the replication lag (seconds to minutes); RTO: minutes (manual promotion). Promoting a cross-region read replica involves manual intervention. The RPO equals the replication lag (which can be seconds to minutes depending on network and workload), not zero. The RTO is measured in minutes because you must verify the replica, promote it, and reconfigure applications. Cloud SQL HA failover (same region) achieves RPO near zero and RTO under 60 seconds, but cross-region replication is asynchronous.

Answer

RPO: up to 1 hour; RTO: up to 24 hours

Answer

RPO: near zero (loss of last few transactions); RTO: under 60 seconds

Answer

RPO: zero; RTO: less than 1 minute

Question 7

A global financial services company requires a multi-region Spanner instance with an RPO of zero and an RTO of less than 5 seconds for a critical transactional workload. The application writes to a single region and reads from multiple regions. Which Spanner configuration should they choose?

Accepted Answer

A two-region multi-region configuration (e.g., nam6). For zero RPO and sub-5-second RTO, a multi-region configuration with synchronous replication is needed. Spanner multi-region configurations like nam6 use synchronous replication across a primary and secondary region (with both read-write replicas). The leader region handles writes, and read-only replicas are for reads. A two-region multi-region config (e.g., nam6) provides synchronous replication (RPO=0) and automatic failover in <5 seconds. Three-region configs (nam-eur-asia1) have higher write latency due to longer distances.

Answer

A single-region configuration with read replicas in multiple zones

Answer

A dual-region configuration with two read-write regions and one read-only region

Answer

A three-region multi-region configuration (e.g., nam-eur-asia1)

Question 8

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 9

A company has a Cloud SQL for MySQL instance with point-in-time recovery (PITR) enabled. They need to restore the database to a specific time exactly 2 hours ago to recover from an accidental data deletion. What is the minimum requirement for this operation?

Accepted Answer

Binary logging must be enabled, and the transaction log retention period must cover the desired restore time. PITR in Cloud SQL relies on binary log (binlog) backups. To restore to a specific time, you need to have binary logging enabled and transaction log retention set appropriately. The binlog retention period determines how far back you can perform PITR. The default is 7 days, but you can configure it. The backup window and number of automatic backups are not directly related to PITR granularity.

Answer

The instance must have a backup window configured within the last 2 hours

Answer

The instance must have at least one automatic backup taken after the desired restore time

Answer

The instance must be stopped before initiating the restore

Question 10

A company uses Cloud Spanner and needs to back up a large database (several TB) for compliance reasons. They want to retain the backup for 400 days. What is the optimal approach to meet this requirement?

Accepted Answer

Export the database to Cloud Storage using Dataflow or an export job, which can be retained indefinitely. Cloud Spanner allows creating backups that can be retained for up to 365 days. For a retention of 400 days, you cannot use a single backup. Instead, you can create a backup and then take another backup before the first expires, or export data to Cloud Storage (e.g., using Dataflow) which has no expiration limit. Using the console, you are limited to 365 days; to exceed that, you must use long-term retention outside of Spanner backups.

Answer

Create a backup with 365-day retention, and before it expires, create another backup to extend coverage

Answer

Create a backup and set the expiration time to 400 days using the gcloud command

Answer

Use continuous PITR to retain transaction logs for 400 days

Question 11

A company needs to ensure that their Cloud SQL for PostgreSQL instance can recover from a zonal failure within 60 seconds with minimal data loss. Which feature should they enable?

Accepted Answer

High availability (HA) configuration. Cloud SQL HA configuration automatically fails over to a standby instance in a different zone within the same region. This failover is automatic and typically completes in under 60 seconds, with near-zero data loss (synchronous replication). Cross-region replicas are manual and have longer RTO. Backups are not suitable for quick recovery.

Answer

Automated backups with PITR

Answer

Cross-region read replica

Answer

Enable deletion protection

Question 12

A company uses Cloud Spanner with a multi-region configuration (nam6) for a global user database. They experience a regional outage affecting us-central1, where the leader region is located. What happens to write availability?

Accepted Answer

Writes automatically fail over to us-east1 within seconds. In a multi-region Spanner configuration like nam6 (us-central1 and us-east1), if the leader region (us-central1) goes down, Spanner automatically fails over to the other region (us-east1) as the new leader. This failover is automatic and typically completes within 5 seconds (RTO <5 seconds). Write availability is restored once the new leader region is elected.

Answer

Writes continue with increased latency because us-central1 is still available for reads

Answer

The Spanner instance becomes read-only until an operator manually fails over

Answer

Writes are blocked until the us-central1 region recovers

Question 13

A company runs a critical application on Cloud SQL for MySQL with an HA configuration. They want to test their disaster recovery plan without affecting production. They need to validate that a cross-region read replica can be promoted successfully in the event of a regional outage. Which approach should they take?

Accepted Answer

Create a clone of the cross-region read replica and promote the clone. To test DR without affecting production, you can promote a cross-region read replica to a standalone instance for testing. However, promoting a read replica stops replication and makes it a writable instance. To avoid impacting production, you should create a clone of the cross-region read replica and promote the clone. Alternatively, you can create a snapshot of the replica and restore to a new instance. The safest way is to create a clone from the replica and promote the clone.

Answer

Promote the cross-region read replica to a standalone instance, then re-create the replica after testing

Answer

Use point-in-time recovery to restore the primary to a new instance in the secondary region

Answer

Create a new read replica in the secondary region and promote that

Question 14

A company needs to choose a Google Cloud database for a globally distributed application that requires strong consistency across continents and an SLA of 99.999% for availability. Which database service meets these requirements?

Accepted Answer

Cloud Spanner. Cloud Spanner is the only Google Cloud database that provides global strong consistency and a 99.999% availability SLA when using a multi-region configuration. Bigtable offers only eventual consistency across regions, Cloud SQL is regional, and Firestore provides strong consistency only within a single region.

Answer

Cloud Bigtable

Answer

Cloud SQL

Answer

Firestore

Question 15

A company runs a Cloud Bigtable instance with two clusters in separate regions for disaster recovery. They want to ensure that read requests automatically use the secondary cluster if the primary cluster becomes unhealthy. Which two steps should they take? (Choose two.)

Accepted Answer

Change the routing policy to 'cluster-group routing' (any-replica). To enable automatic failover for reads in Bigtable, you need to use a routing policy that distributes reads across clusters. The 'cluster-group routing' (also called 'any-replica' routing) automatically routes requests to the nearest healthy cluster. Additionally, you must configure the application to use this routing policy. Alternatively, you can use a load balancer with health checks, but that is not native to Bigtable. The correct native approach is to use cluster-group routing and ensure the application uses it.

Answer

Set up a load balancer in front of Bigtable instances

Answer

Create a third cluster in a third region for quorum

Answer

Configure Cloud DNS with a health check that points to the secondary cluster

Question 16

A company is designing a disaster recovery strategy for a Cloud SQL for PostgreSQL instance. They require an RPO of less than 5 minutes and an RTO of less than 2 minutes in the event of a regional outage. Which three components should they include in their solution? (Choose three.)

Accepted Answer

Cross-region read replica. To achieve RPO <5 minutes and RTO <2 minutes across regions, you need a solution that can recover quickly with minimal data loss. Cloud SQL cross-region read replicas replicate asynchronously, so RPO is the replication lag (which can be <5 minutes if the network is fast). Promoting a read replica manually takes minutes, but you can automate the promotion using Cloud Functions or scripts to reduce RTO. Alternatively, you could use a standby instance in another region with synchronous replication (but Cloud SQL does not support that). The best approach is to use a cross-region read replica with automated promotion (e.g., via Cloud Functions triggered by a health check). Additionally, you need to update application connection strings to point to the new primary. Using a load balancer with health checks can also help route traffic. The three correct components are: cross-region read replica, automated promotion script, and a global load balancer to redirect traffic.

Answer

Point-in-time recovery enabled with 7-day retention

Answer

Automated backup with 5-minute frequency

Question 17

A company uses Cloud Spanner with a single-region configuration in us-central1. They need to improve disaster recovery to meet an RPO of zero and an RTO of less than 5 seconds across regions. Which three actions should they take? (Choose three.)

Accepted Answer

Use backup/restore to migrate data from the single-region instance to the new multi-region instance. To achieve RPO=0 and RTO<5s across regions, you need a multi-region Spanner configuration with synchronous replication. You cannot achieve cross-region RPO=0 with a single-region instance. Therefore, you must migrate to a multi-region configuration. The steps include: 1) Create a new multi-region instance (e.g., nam6) with the desired config, 2) Migrate data from the single-region instance to the multi-region instance (e.g., using backup/restore or Dataflow), 3) Update application connection strings to point to the new instance. Optionally, you can perform a rolling migration to minimize downtime. Using cross-region read replicas is not possible for Spanner (Spanner does not have read replicas in the same sense; it uses replica types within an instance).

Answer

Add a cross-region read replica to the existing single-region instance

Answer

Enable point-in-time recovery (PITR) with 7-day retention

Question 18

A company needs to store petabytes of time-series IoT sensor data and query it with single-digit millisecond latency at millions of reads per second. The data has a simple key-value structure with timestamps. Which Google Cloud database is MOST appropriate?

Accepted Answer

Cloud Bigtable. Cloud Bigtable is designed for exactly this use case — petabyte-scale, low-latency (single-digit ms), high-throughput NoSQL storage for time-series, IoT, and financial data. It scales horizontally by adding nodes. BigQuery is optimised for analytics (seconds-to-minutes latency), Cloud SQL is for OLTP (limited to tens of thousands of QPS), and Firestore is for document data with hierarchical structure.

Answer

BigQuery

Answer

Cloud Spanner

Answer

Firestore

Question 19

A Cloud SQL for PostgreSQL instance needs to achieve a recovery point objective (RPO) of less than 1 minute and a recovery time objective (RTO) of less than 2 minutes in the event of a zone failure. Which disaster recovery strategy should be used?

Accepted Answer

Configure Cloud SQL HA (high availability) with a standby in a different zone.. Cloud SQL HA configuration provides automatic failover to a standby in a different zone within the same region, with RPO near zero and RTO typically under 60 seconds. Cross-region read replicas have RPO equal to replication lag (could be minutes) and RTO of minutes due to manual promotion. Cross-region backup restore has RPO equal to backup age (hours) and RTO of hours. Point-in-time recovery (PITR) is for within-region data recovery, not zone failure failover.

Answer

Perform regular backups to Cloud Storage and restore in a different zone.

Answer

Enable cross-region replication using a read replica.

Answer

Enable point-in-time recovery (PITR) with transaction log backups.

Question 20

A global e-commerce platform uses Cloud Spanner in multi-region configuration. The application writes a significant portion of traffic from Europe and requires the lowest read latency in that region. Which configuration step should be taken to minimise read latency in Europe while maintaining write availability?

Accepted Answer

Set the leader region to Europe (e.g., eur3).. In Spanner multi-region, the leader region determines where writes are committed. Setting the leader region to Europe ensures that writes are committed there, which reduces write latency for European traffic. Read-only replicas in other regions can serve reads with low latency without affecting write availability. Adding more read replicas in Europe would not reduce latency if the leader region is elsewhere. The number of read-write replicas does not directly reduce read latency. Splitting the database would not help for a single database.

Answer

Configure a separate Spanner instance for European traffic and split the database.

Answer

Add more read-write replicas in the European region.

Answer

Use a regional Spanner instance in Europe coupled with a copy of the data in Bigtable.