PCDE Manage a solution that can span multiple database technologies — 20 Questions

Question 1

Your Cloud Bigtable instance uses HDD storage. You need to change to SSD to improve read performance. What is the correct procedure?

Accepted Answer

Create a new cluster with SSD storage in the same instance, replicate data, then delete the old cluster.. Cloud Bigtable does not support changing the storage type (HDD to SSD) on an existing cluster. Option A is incorrect because there is no online migration feature. Option B is incorrect because the 'gcloud bigtable instances update' command does not allow changing the storage type. Option D is possible but involves more downtime and complexity. Option C is correct: create a new cluster with SSD in the same instance, replicate data using replication, then delete the old HDD cluster. This minimizes downtime and is the recommended approach.

Answer

Use Cloud Bigtable's online storage migration feature to switch to SSD without downtime.

Answer

Update the instance's storage type using 'gcloud bigtable instances update' with the --storage-type flag.

Answer

Export the HDD cluster's data to Cloud Storage, then import into a new SSD cluster.

Question 2

A development team uses Cloud Spanner and needs to add a new index to a table with 10 TB of data. They require that the operation does not block writes or cause downtime. Which approach should they take?

Accepted Answer

Execute 'CREATE INDEX' statement; Spanner will build the index in the background without blocking.. In Cloud Spanner, executing a CREATE INDEX statement is a non-blocking operation. Spanner builds the index in the background while the table remains fully available for reads and writes, thus avoiding downtime. Option C is correct. Option A (create new table and copy data) is unnecessary and complex. Option B (maintenance window) is not needed because Spanner handles online schema changes. Option D (drop and recreate) causes downtime and data loss risk.

Answer

Create a new table with the index and batch copy data from the original table.

Answer

Schedule a maintenance window, then create the index during the window.

Answer

Drop the table and recreate it with the index, then restore from backup.

Question 3

A company is using Cloud Firestore to store user profiles. They need to query users by both their 'age' and 'city' fields. What must they configure to perform this query efficiently?

Accepted Answer

Create a composite index on age and city.. Firestore automatically creates single-field indexes for simple queries. However, for queries filtering on multiple fields like 'age' and 'city', a composite index must be created manually. Therefore, Option D is correct. Option A (single-field indexes) is insufficient. Option B (index exemptions) is for arrays and maps, not for multi-field queries. Option C (Datastore mode) does not change this requirement.

Answer

Use Firestore in Datastore mode for automatic composite indexes.

Answer

Configure index exemptions for the fields.

Answer

No configuration needed; single-field indexes are sufficient.

Question 4

An engineer is managing a Cloud Spanner database and needs to add a new column to an existing table without downtime. Which approach should be used?

Accepted Answer

Use ALTER TABLE ADD COLUMN statement. In Cloud Spanner, adding a new column to an existing table without downtime is achieved using the ALTER TABLE ADD COLUMN statement. This DDL operation is applied online, meaning the table remains fully available for reads and writes during the schema change, with no need for data migration or table recreation.

Answer

Export the database, modify the schema, and import using Dataflow

Answer

Use CREATE INDEX for the new column

Answer

Drop and recreate the table with the new column

Question 5

You are using Memorystore for Redis with persistence disabled. Your application requires that no data is lost in the event of a node failure. What should you do to achieve this requirement?

Accepted Answer

Enable AOF persistence in Memorystore.. Enabling AOF (Append-Only File) persistence ensures that every write operation is logged to disk. In the event of a node failure, the data can be recovered from the AOF file, preventing data loss even though persistence was initially disabled. Option A is incorrect because Memorystore for Redis does not support cross-region replicas; replication is limited to within the same region. Option C is insufficient because on-demand backups are not real-time and data written after the last backup would be lost. Option D is irrelevant as increasing maxmemory does not provide durability.

Answer

Configure a cross-region replica to provide failover and data durability.

Answer

Take regular on-demand backups using gcloud redis instances export.

Answer

Increase the maxmemory setting to store more data.

Question 6

You are designing a disaster recovery strategy for a Cloud SQL for MySQL instance that hosts a critical OLTP application. The instance is in us-central1. You need to ensure that you can recover the database to a different region within 1 hour of a regional outage, with minimal data loss. Which TWO actions should you take? (Choose TWO.)

Accepted Answer

Enable automated backups and point-in-time recovery with a 7-day retention.. Enabling automated backups with point-in-time recovery (PITR) allows you to restore the database to any point within the retention window (here, 7 days), minimizing data loss to seconds. Option E is correct because a cross-region read replica in us-west1 can be promoted to a standalone primary instance in the event of a regional outage, providing a fully writable database in another region within minutes, meeting the 1-hour RTO.

Answer

Take daily on-demand exports to Cloud Storage.

Answer

Create two cross-region read replicas for redundancy.

Answer

Increase the instance tier to have more memory.

Question 7

A company uses Cloud Spanner and wants to export a database for long-term archival. The export must include the schema in a portable format. Which export option should they choose?

Accepted Answer

Create a database-level backup from the Cloud Console; it will export data and schema as Avro + Protobuf.. Spanner database backups are stored in Cloud Storage as Avro files with a Protobuf schema file, preserving both data and schema.

Answer

Manually run SELECT statements to export data and DESCRIBE commands for schema.

Answer

Use the Spanner migration tool to export to a SQL dump file.

Answer

Use gcloud spanner databases export with the --async flag to export to a Cloud Storage bucket in Avro format.

Question 8

A company uses Cloud Spanner and needs to export a full database to Cloud Storage in a format that preserves both the schema and data for long-term archival. The export must be restorable into a new Spanner database later. Which export method should they use?

Accepted Answer

Use gcloud spanner databases export to export the data to Cloud Storage in CSV format.. The `gcloud spanner databases export` command exports the database to Cloud Storage in Avro format, preserving both schema and data. This exported data can be used for long-term archival and can be restored into a new Spanner database using the import command. Backups created with `gcloud spanner databases backup create` are stored internally and are not directly accessible in a user-managed Cloud Storage bucket for archival purposes.

Answer

Use gcloud spanner databases backup create to create a backup that is stored in Cloud Storage.

Answer

Use Dataflow to read the Spanner tables and write them to Cloud Storage as Parquet files.

Answer

Use gcloud spanner databases restore to copy the database to a new instance.

Question 9

A company uses Bigtable and wants to change the storage type from HDD to SSD to improve read performance. What must the engineer do to implement this change?

Accepted Answer

Create a new cluster with SSD, replicate data to it, then delete the old cluster.. Bigtable does not support in-place conversion of a cluster's storage type from HDD to SSD. The correct approach is to create a new cluster with SSD storage, configure replication to replicate data from the existing HDD cluster to the new SSD cluster, and then delete the old HDD cluster. This ensures zero downtime and data consistency during the migration.

Answer

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

Answer

Modify the cluster settings and change the storage type to SSD.

Answer

Export the data to Cloud Storage, create a new SSD cluster, and import the data.

Question 10

A company uses Cloud SQL for MySQL with automated backups enabled. They want to ensure they can recover their database in the event of a regional outage. Which TWO actions should they take? (Choose two.)

Accepted Answer

Create a cross-region read replica.. A cross-region read replica in Cloud SQL for MySQL provides a standby copy of the database in a different region, which can be promoted to a primary instance during a regional outage, enabling recovery with minimal data loss. Option C is correct because cross-region backup replicas (also known as cross-region backup copies) allow backups to be stored in a separate region, ensuring that backup data survives a regional disaster and can be used to restore the database in another region.

Answer

Increase the backup retention period to 30 days.

Answer

Enable point-in-time recovery with a 7-day retention.

Answer

Schedule more frequent on-demand backups.

Question 11

A Memorystore for Redis instance is running out of memory and evicting keys. The application requires critical keys to be retained. The team wants to implement an eviction policy that removes less recently used keys first. Which eviction policy should they configure?

Accepted Answer

volatile-lru. The volatile-lru eviction policy is correct because it removes the least recently used keys among those that have an expiration (TTL) set, which allows the application to retain critical keys that are not given a TTL. This policy ensures that only volatile keys are candidates for eviction, protecting non-expiring keys from being removed when memory is exhausted.

Answer

noeviction

Answer

allkeys-lru

Answer

volatile-ttl

Question 12

A Cloud Spanner database needs a new index added to support a new query pattern. The database is serving live traffic. Which approach should be taken?

Accepted Answer

Create the index using DDL statement 'CREATE INDEX' — it will be applied online without downtime.. Cloud Spanner supports online schema changes, including index creation, without downtime. The 'CREATE INDEX' DDL statement is applied asynchronously in the background, allowing the database to continue serving live traffic while the index is built. This is the correct approach because it avoids any interruption to the application.

Answer

Export the data, create a new database with the index, and import the data.

Answer

Stop the application, add the index, and restart.

Answer

Use gcloud spanner databases add-index command.

Question 13

A team needs to monitor CPU utilization on Cloud SQL databases and receive an alert when it exceeds 80% for more than 5 minutes. Which Google Cloud service should they use?

Accepted Answer

Cloud Monitoring. Cloud Monitoring (formerly Stackdriver Monitoring) is the correct service because it provides built-in metrics for Cloud SQL, including CPU utilization, and allows you to create alerting policies based on threshold conditions (e.g., CPU > 80% for 5 minutes). It integrates directly with Cloud SQL and can trigger notifications via email, Pub/Sub, or other channels when the condition is met.

Answer

Cloud Audit Logs

Answer

Active Assist

Answer

Cloud Logging

Question 14

A Firestore database in Native mode has a collection with a composite index on fields (city, age). A new query filters on 'city == 'London' AND 'age > 30' ORDER BY 'name'. The query is slow and reads many documents. What should the engineer do?

Accepted Answer

Create a composite index on (city, age, name).. The query filters on `city == 'London'` and `age > 30`, then orders by `name`. For Firestore to efficiently satisfy both the equality and inequality filters combined with an `ORDER BY`, the composite index must include the fields in the correct order: equality fields first, then the inequality field, then the sort field. Option C provides the index `(city, age, name)`, which matches this pattern exactly, allowing Firestore to perform a targeted index scan without reading extra documents.

Answer

Remove the ORDER BY clause to improve performance.

Answer

Create a composite index on (city, name).

Answer

Create a single-field index on 'name'.

Question 15

A company is migrating on-premises MySQL databases to Cloud SQL. They need to ensure high availability and disaster recovery with minimal data loss. Which TWO configurations should they implement?

Accepted Answer

Enable High Availability (HA) configuration on the primary instance.. Enabling High Availability (HA) configuration on a Cloud SQL primary instance creates a synchronous standby in a different zone within the same region, providing automatic failover with minimal data loss (typically under one second). This directly addresses the need for high availability with minimal data loss during a zonal outage.

Answer

Configure automated backups with 7-day retention.

Answer

Use Cloud SQL Proxy for secure connections.

Answer

Enable binary logging for point-in-time recovery.

Question 16

A company uses Cloud Spanner for a global inventory system. They need to add a new index on an existing table to support a new query pattern without downtime. What is the correct approach to create the index?

Accepted Answer

Use the gcloud CLI to create the index; Spanner handles it as an online, non-blocking operation. Cloud Spanner supports online schema changes, including index creation, without requiring downtime. When you use the gcloud CLI or the Cloud Console to create an index, Spanner performs the operation as a non-blocking, asynchronous background process that allows continued reads and writes on the table.

Answer

Create a new table with the index and migrate data manually

Answer

Use the Cloud Console to create the index; it requires a maintenance window

Answer

Take the table offline, create the index, then bring it back online

Question 17

A company is using Memorystore for Redis and needs to persist data across restarts. Which option should they use?

Accepted Answer

Take periodic snapshots and store them in Cloud Storage. Memorystore for Redis does not natively support AOF persistence; it relies on periodic RDB snapshots to persist data. By taking these snapshots and storing them in Cloud Storage, you can restore the Redis instance after a restart or failure, ensuring data durability across restarts.

Answer

Enable AOF persistence in Memorystore settings

Answer

Use a standard tier instance with persistence enabled

Answer

Enable auto-backup in Memorystore

Question 18

A company is using Memorystore for Redis as a session store. They need to scale horizontally to handle increasing traffic and ensure high availability with automatic failover. Which TWO actions should they take?

Accepted Answer

Enable Redis Cluster mode (sharding). Memorystore for Redis supports sharding for horizontal scaling, and standard tier provides replication with automatic failover.

Answer

Create multiple standalone instances and route traffic manually

Answer

Use Persistent Disk for data persistence

Answer

Use the Basic tier

Question 19

An engineer needs to restore a Cloud Spanner database from a backup that was taken 2 hours ago. The backup is stored in Cloud Storage. What steps are required?

Accepted Answer

Use gcloud spanner databases restore --backup= --destination-database=. Cloud Spanner backups are not stored directly in Cloud Storage; they are stored within the instance's internal backup storage. The question's mention of 'stored in Cloud Storage' is a common misstatement. The correct restoration method uses the `gcloud spanner databases restore` command with a backup ID, as shown in option A. Import/export uses Cloud Storage, but that is a different process.

Answer

Create a new instance and use gcloud spanner instances restore.

Answer

Use gcloud spanner databases import from the Cloud Storage backup file.

Answer

Restore is not possible; you must use point-in-time recovery.

Question 20

A Bigtable instance is experiencing high latency and uneven load distribution. The operations team suspects a hot spot. Which tool should they use to identify the hot spot, and what action can they take to mitigate it?

Accepted Answer

Use Key Visualiser to identify the hot row/key; then redesign the row key to distribute load.. Key Visualizer is the correct tool for identifying hot spots in Cloud Bigtable because it provides a heatmap of row key access patterns, allowing you to pinpoint specific rows or key ranges causing uneven load. Once identified, redesigning the row key (e.g., by salting or reversing keys) distributes writes and reads across nodes, mitigating the hot spot without requiring manual table splits or storage changes.

Answer

Use 'gcloud bigtable hot-spots list' command; then split the hot table into multiple tables.

Answer

Use Cloud Monitoring to check CPU utilisation; then add more nodes to the cluster.

Answer

Use the Bigtable admin console to view table statistics; then change the storage type from HDD to SSD.