PCDE Manage a solution that can span multiple database technologies Practice Test 7 — 15 Questions

Question 1

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?

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

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 2

A financial services company uses Cloud Spanner for a globally distributed application. They need to add a new column to an existing table that contains billions of rows. The change must not cause any downtime or performance degradation. How should the engineer implement this schema change?

Accepted Answer

Use ALTER TABLE ADD COLUMN; Spanner applies the change online without downtime.. Cloud Spanner supports online schema changes via the `ALTER TABLE ADD COLUMN` statement, which applies the change asynchronously without locking the table or causing downtime. Spanner uses a multi-phase approach to add columns, allowing reads and writes to continue uninterrupted while the schema change propagates across all nodes and regions.

Answer

Export the table, modify the schema in a temporary table, and import it back.

Answer

Use CREATE INDEX to add the column as an index.

Answer

Create a new table with the additional column, backfill data from the old table, then rename the tables.

Question 3

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 4

A data analytics company uses Bigtable for high-throughput writes. They notice that some rows are receiving a disproportionate number of reads and writes, causing performance degradation. Which tool should they use to identify and resolve this hot spotting issue?

Accepted Answer

Key Visualiser. Key Visualizer is the correct tool because it is specifically designed to analyze Bigtable access patterns and visualize hot spotting—where a small number of rows or row ranges receive a disproportionate share of reads and writes. It provides heatmaps and time-series graphs that pinpoint the exact keys causing performance degradation, enabling you to redesign your row keys or implement salting to distribute load evenly.

Answer

cbt tool

Answer

Cloud Logging

Answer

Cloud Monitoring

Question 5

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 6

A company uses Memorystore for Redis with Standard Tier (replication) and needs to ensure data durability in case of a zone failure. They also need to scale read throughput beyond a single instance. What should they do?

Accepted Answer

Migrate to Redis Cluster with 3+ shards.. Memorystore for Redis Standard Tier provides cross-zone replication for high availability. To scale read throughput, they can use Redis Cluster (which shards data across multiple shards) or create read replicas. However, Memorystore does not support read replicas for Redis; instead, Redis Cluster provides horizontal scalability and high availability. Upgrading to a larger instance scales vertically but not read throughput horizontally. Persistence is not natively supported in Memorystore.

Answer

Create a cross-region replica and use it for read traffic.

Answer

Upgrade to a larger machine type with more memory.

Answer

Enable persistence using AOF and configure a backup schedule.

Question 7

A Cloud SQL for PostgreSQL instance is running out of storage. The engineer wants to configure automatic storage increase to avoid manual intervention. What should they do?

Accepted Answer

Use gcloud sql instances patch with the --storage-auto-increase flag.. Cloud SQL for PostgreSQL supports automatic storage increase, which can be enabled via the `--storage-auto-increase` flag in the `gcloud sql instances patch` command. This feature automatically increases the instance's storage capacity when it approaches the configured limit, eliminating the need for manual intervention.

Answer

Use gcloud sql instances patch with the --disk-size flag to set a larger size.

Answer

Create a cron job to monitor disk usage and increase storage via API.

Answer

Use gcloud sql instances create to create a new instance with larger storage.

Question 8

A company uses Firestore in Native mode for their application. They need to query a collection where documents must match a specific field value and be sorted by a different field. The query filters on 'status' and orders by 'timestamp'. What should the engineer do to ensure the query performs optimally?

Accepted Answer

Create a composite index on the 'status' and 'timestamp' fields.. Firestore requires a composite index when a query includes both an equality filter on one field (status) and an order by clause on a different field (timestamp). Without this composite index, Firestore cannot efficiently satisfy both the filter and the sort order in a single index scan, leading to suboptimal performance or query failure. Creating a composite index on (status, timestamp) allows Firestore to use a single index to match the filter and return results in the requested order.

Answer

Create an index exemption to improve query performance.

Answer

Use a collection group query to bypass index requirements.

Answer

Rely on automatic single-field indexes; they will cover the query.

Question 9

An engineer needs to monitor the replication lag of a Cloud SQL read replica. Which metric should they use in Cloud Monitoring?

Accepted Answer

replication_lag. The `replication_lag` metric in Cloud Monitoring directly measures the time delay between a primary Cloud SQL instance and its read replica, reported in seconds. This is the standard metric for monitoring how far behind the replica is in applying changes from the primary, which is critical for ensuring read-after-write consistency and data freshness.

Answer

sent_bytes_count

Answer

disk_bytes_used

Answer

cpu_utilization

Question 10

A company uses Memorystore for Redis and wants to achieve high availability with automatic failover. They also need to periodically back up the data to Cloud Storage for disaster recovery. Which TWO features should they use? (Choose two.)

Accepted Answer

Standard Tier (replication). Standard Tier (replication) provides a primary-replica architecture with automatic failover, ensuring high availability. The Export functionality allows you to manually or scheduled export Redis data to Cloud Storage, enabling point-in-time recovery for disaster recovery purposes.

Answer

Redis Cluster

Answer

AOF persistence

Answer

Basic Tier

Question 11

A company uses Cloud Spanner and needs to capture real-time changes from a table for downstream processing. They want to avoid writing custom application code to track changes. Which THREE components should they use? (Choose three.)

Accepted Answer

Pub/Sub. Cloud Spanner Change Streams (option C) capture real-time changes (inserts, updates, deletes) from a table. These changes are automatically published to a Pub/Sub topic (option B). A subscriber can then use Dataflow (option E) to process the change stream messages for downstream transformations or loading. Cloud Bigtable (option A) is a different database service not involved in this scenario. The Cloud Spanner API (option D) is not needed because Change Streams already integrate with Pub/Sub.

Answer

Cloud Bigtable

Answer

Cloud Spanner API

Question 12

A company is running a Cloud SQL for PostgreSQL instance for an e-commerce application. They need to enable point-in-time recovery (PITR) with a 7-day retention period. What configuration steps must be taken?

Accepted Answer

Enable WAL archiving and configure backup retention to 7 days using gcloud sql instances patch --backup-retention-days 7.. Cloud SQL for PostgreSQL uses Write-Ahead Log (WAL) archiving to enable point-in-time recovery (PITR). You must enable automated backups (which automatically enables WAL archiving) and then set the backup retention period to 7 days using the `gcloud sql instances patch --backup-retention-days 7` command. This ensures that WAL logs are retained for the specified duration, allowing PITR within that window.

Answer

Create a cross-region backup replica with a 7-day retention.

Answer

Enable binary logging and set backup retention to 7 days.

Answer

Enable automated backups with a 7-day retention; WAL archiving is automatic.

Question 13

A team wants to create a Cloud Spanner database backup and store it in a Cloud Storage bucket for long-term archival. Which method should they use?

Accepted Answer

Use the gcloud spanner databases backup command to create a backup that resides in Cloud Storage.. Cloud Spanner provides database-level backups directly to Cloud Storage in Avro + Protobuf format. Export/import is for migration, not archival backups.

Answer

Use gcloud spanner instances create-backup to create a backup of the instance.

Answer

Take a snapshot of the Spanner instance using Cloud Storage snapshots.

Answer

Use the gcloud spanner databases export command to export to Cloud Storage.

Question 14

A Cloud Bigtable instance is experiencing high read latency due to hot spots. The operations team uses the Key Visualizer tool and identifies that a small set of row keys are being read disproportionately. Which action should they take to mitigate the hot spotting?

Accepted Answer

Redesign the row key scheme to distribute the workload across more tablets.. Hot spotting in Cloud Bigtable is typically caused by a suboptimal row key design that concentrates read/write traffic on a small number of tablets. Redesigning the row key scheme to distribute the workload—for example, by adding a hash prefix or using a more granular key—spreads requests across multiple tablets, alleviating the hotspot. Key Visualizer explicitly identifies the skewed row keys, guiding the redesign effort.

Answer

Increase the number of nodes in the Bigtable cluster to handle the load.

Answer

Change the storage type from HDD to SSD to improve performance.

Answer

Enable replication across multiple zones.

Question 15

An application uses Firestore in Native mode. The query filters on two fields: 'status' (string) and 'created_date' (timestamp). The query returns results but the billing shows high document reads. What is the most likely cause?

Accepted Answer

The query is using an inequality filter on 'created_date' which requires a composite index.. In Firestore Native mode, queries that apply an inequality filter (e.g., >=, >, <, !=) on a field automatically require a composite index on both the equality filter field and the inequality filter field to avoid a full collection scan. Without that composite index, Firestore performs a back-end scan of all documents matching the equality filter, then applies the inequality filter in memory, resulting in high document reads. Option A correctly identifies that the inequality filter on 'created_date' is the most likely cause of the excessive reads because it forces Firestore to read and discard many documents that do not satisfy the timestamp condition.

Answer

The query is using 'array-contains' which always scans the entire collection.

Answer

The 'status' field is not indexed because single-field indexes are not automatic.

Answer

The query is missing an ORDER BY clause causing a full scan.