PCDE Manage a solution that can span multiple database technologies Practice Test 10 — 15 Questions

Question 1

A company runs a Cloud Bigtable instance with SSD storage and wants to switch to HDD storage to reduce costs. The instance cannot tolerate downtime for data migration. What is the correct approach?

Accepted Answer

Create a new Cloud Bigtable cluster with HDD storage and migrate data. Cloud Bigtable does not support in-place conversion of storage type from SSD to HDD. The only way to switch storage without downtime is to create a new cluster with HDD storage, then use a replicated setup (e.g., via a replication cluster or application-level dual-write) to migrate data while the original cluster remains operational. This ensures zero downtime during the migration.

Answer

Increase the number of nodes to reduce per-node cost

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Add a cross-region replica and then promote it with HDD storage

Answer

Use the gcloud bigtable clusters update command to change storage type

Question 2

A company uses Memorystore for Redis with the 'volatile-lru' eviction policy. They notice that recently added keys with TTL are being evicted even though there is still memory available. What is the most likely cause?

Accepted Answer

The volatile-lru policy evicts only keys with an expiry set, and there are many keys without expiry occupying memory. The 'volatile-lru' eviction policy in Memorystore for Redis evicts only keys that have a TTL (expiry) set, using an LRU (Least Recently Used) algorithm among those keys. If many keys without expiry are consuming memory, the eviction process will still target only the volatile keys, even if overall memory is not fully exhausted, because the policy is constrained to evict only from the subset of keys with TTLs. This explains why recently added keys with TTL are being evicted prematurely — the non-volatile keys are 'protected' from eviction, forcing the eviction of volatile keys to free memory.

Answer

The allkeys-lru policy would be more appropriate

Answer

The maxmemory setting is not configured

Answer

The maxmemory-policy is misconfigured

Question 3

A Cloud Spanner database has a table with a primary key and a secondary index. The application frequently queries using a filter on the secondary index column and orders by the primary key. The queries are slow. What should the database administrator do to improve query performance?

Accepted Answer

Create a covering index using CREATE INDEX with the STORING clause to include the required columns. Creating a covering index with the STORING clause lets Cloud Spanner satisfy the query entirely from the index without a back-join to the base table, eliminating the expensive lookup for each row. Because the query filters on the indexed column and orders by the primary key, storing the needed columns in the index makes the index itself sufficient to return results. This directly addresses the slow query by removing the extra read hop.

Answer

Increase the number of nodes to improve query throughput

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Create an interleaved table that mirrors the data

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Use ALTER TABLE to add a new index on the filter column

Question 4

A company uses Firestore in Native mode and has a collection with many documents containing array fields. They want to index the array values to support queries like 'array-contains'. What is the correct approach?

Accepted Answer

No additional index configuration is required; arrays are automatically indexed. Firestore in Native mode automatically indexes all fields within documents, including array fields, so queries using 'array-contains' work without any manual index creation. Single-field indexes are created by default for every field in a collection, which is why no additional configuration is needed for basic array queries. This automatic indexing is a core design feature of Firestore that differentiates it from Datastore mode.

Answer

Create an index exemption for the array field to enable indexing

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Switch to Datastore mode and configure indexes manually

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Create a composite index that includes the array field

Question 5

A company wants to use Cloud SQL for MySQL to serve a read-heavy application. They need to ensure high availability and offload read traffic. Which TWO steps should they take? (Choose two.)

Accepted Answer

Create a same-region read replica. Option E is correct because enabling high availability (HA) on the primary Cloud SQL for MySQL instance provisions a standby replica in a different zone within the same region, providing automatic failover and meeting the high-availability requirement. Option C is correct because a same-region read replica serves read traffic from a separate instance, offloading the primary and improving read scalability while keeping latency low. Option A is incorrect because daily on-demand backups provide data protection and point-in-time recovery, not high availability or read offloading. Option B is incorrect because a cross-region read replica is primarily for disaster recovery and read scaling across regions, and it is not the standard way to achieve HA for the primary instance. Option D is incorrect because auto-storage increase only handles disk growth automatically and does not address availability or read traffic.

Answer

Schedule on-demand backups daily

Answer

Create a cross-region read replica

Answer

Enable auto-storage increase

Question 6

A developer wants to add a composite index in Firestore to support a query that filters on two fields: 'status' (equality) and 'createdAt' (range). How should the index be configured?

Accepted Answer

Create a composite index with fields 'status' (ascending) and 'createdAt' (ascending).. Firestore requires a composite index when a query combines an equality filter on one field with a range filter on another. The index must list the equality field first ('status') followed by the range field ('createdAt'), with ascending order for both to support the range query efficiently. This matches the Firestore index definition rules for composite indexes.

Answer

No index is needed; single-field indexes are automatically created.

Answer

Create a composite index with fields 'createdAt' (ascending) and 'status' (ascending).

Answer

Add an index exemption on the 'status' field to force index creation.

Question 7

You are using Cloud Spanner and need to add a new column to an existing table. The table has millions of rows and must remain fully available for reads and writes during the schema change. What is the correct approach?

Accepted Answer

Use gcloud spanner databases ddl update with the ALTER TABLE statement; Spanner applies the change online.. Cloud Spanner supports online schema changes using DDL statements executed via `gcloud spanner databases ddl update`. The ALTER TABLE statement adds the column without locking the table or requiring downtime; Spanner applies the change in the background while the table remains fully available for reads and writes. This is the standard, supported method for schema modifications in Spanner.

Answer

Export the table using Dataflow, add the column locally, then import the data back.

Answer

Use gcloud spanner instances update to modify the table schema.

Answer

Take the instance offline, run the ALTER TABLE, then bring it back online.

Question 8

You notice that your Cloud SQL for MySQL instance's storage is filling up quickly. You have enabled automatic storage increase, but you want to manually increase the storage size by 50 GB to avoid any risk of reaching the limit. The current disk size is 200 GB. What is the correct gcloud command to resize the disk?

Accepted Answer

gcloud sql instances patch my-instance --storage-size 250. The `gcloud sql instances patch` command is used to modify an existing Cloud SQL instance, and the `--storage-size` flag expects the value in GB as an integer (without the 'GB' suffix). Specifying `250` correctly increases the storage from 200 GB to 250 GB.

Answer

gcloud sql instances patch my-instance --storage-size 250GB

Answer

gcloud sql instances update my-instance --storage-size 250

Answer

gcloud sql instances resize my-instance 250

Question 9

You need to monitor the disk usage of your Cloud SQL instances and receive an alert when disk usage exceeds 80%. Which GCP service should you use to set up this alert?

Accepted Answer

Cloud Monitoring. Cloud Monitoring (formerly Stackdriver) is GCP's native service for collecting metrics, creating alerting policies, and notifying on thresholds such as disk usage exceeding 80%. Cloud SQL instances automatically publish metrics like `disk/utilization` to Cloud Monitoring, so you can create an alerting policy on that metric with an 80% threshold. This is the standard, supported way to monitor and alert on Cloud SQL resource usage.

Answer

Cloud Audit Logs

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Cloud Logging

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Cloud Billing reports

Question 10

You have a Cloud Bigtable instance with a single cluster. To improve availability and durability, you want to enable replication across two regions. After configuring replication, you notice that reads from the replica cluster show data that is not yet consistent with the primary. What is the expected consistency model for Bigtable replication?

Accepted Answer

Eventually consistent reads from replicas. Cloud Bigtable replication uses an eventually consistent model for reads from replica clusters. When you write to the primary cluster, the data is asynchronously replicated to the replica cluster using a distributed replication pipeline. This means that reads from the replica cluster may return stale data until the replication process completes, and there is no guarantee of immediate consistency with the primary.

Answer

Read-your-writes consistency from the primary

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Strongly consistent reads from any cluster

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Strict serializability across clusters

Question 11

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 12

You are troubleshooting a Cloud SQL read replica that is experiencing high replication lag. You check the 'replication_lag' metric and see it is consistently above 60 seconds. What is the most likely cause of this lag?

Accepted Answer

The primary instance has a heavy write workload.. High replication lag in Cloud SQL is most commonly caused by a heavy write workload on the primary instance. When the primary processes a large volume of write operations (e.g., INSERT, UPDATE, DELETE), the replica must replay those changes from the binary log, and if the rate of writes exceeds the replica's ability to apply them, lag accumulates. This is a fundamental behavior of MySQL asynchronous replication, where the replica is always slightly behind the primary under load.

Answer

The replica's automatic storage increase is disabled.

Answer

The replica has point-in-time recovery enabled.

Answer

The replica is using a different storage type than the primary.

Question 13

Your Cloud Bigtable instance is experiencing hot spots, causing performance degradation. You want to identify the specific row keys causing the hot spots. Which tool should you use?

Accepted Answer

Key Visualiser. The Key Visualiser is a tool provided by Google Cloud for Cloud Bigtable that analyzes row key distribution and identifies hot spots by visualizing the access patterns of row keys. It helps you understand which specific row keys are causing performance degradation due to uneven load. By using the Key Visualiser, you can pinpoint the problematic keys and then redesign your schema or application logic to distribute the load more evenly.

Answer

Cloud Monitoring dashboard

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cbt command-line tool

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Cloud Logging

Question 14

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. Option B is also a valid DR concept using cross-region read replicas, but because the question asks for TWO actions and B duplicates the action in E, the intended correct pair is D and E.

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 15

You are managing a Memorystore for Redis instance that is part of a high-traffic e-commerce application. The instance uses the volatile-lru eviction policy and has persistence disabled. You need to improve data durability without losing the ability to evict keys with TTL. You also want to ensure that the instance can automatically recover from a zonal failure. Which TWO actions should you take? (Choose TWO.)

Accepted Answer

Enable RDB persistence by setting the persistence mode.. (Enable RDB persistence) improves data durability by taking periodic snapshots without interfering with the volatile-lru eviction policy, which only evicts keys with TTL. Option D (Standard Tier with replication) provides automatic failover across zones within a region, ensuring recovery from a zonal failure. Option A only reduces eviction frequency but does not address durability or zonal failover. Option C is incorrect because Memorystore does not support native cross-region replicas. Option E uses manual exports, which do not enable automatic recovery and are not equivalent to persistence.

Answer

Increase the maxmemory setting to reduce eviction frequency.

Answer

Configure a cross-region replica to provide failover in another region.

Answer

Set up a Cloud Scheduler job to export the instance to Cloud Storage every hour.