PCD Practice Test 6 — 10 Questions

Question 1

An e-commerce platform uses Cloud SQL MySQL for orders and Bigtable for session history. To provide a unified customer view, they need to join order data with recent session activity. Which approach minimises data movement while achieving low-latency queries?

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

Accepted Answer

Use Memorystore as a cache to store denormalised customer views, updated from both databases.. Memorystore (Redis) can cache frequently accessed session data from Bigtable and order data from Cloud SQL, enabling low-latency reads without moving data permanently. Dataflow is batch-oriented, Cloud Functions is not for queries, and exporting to BigQuery adds latency.

Answer

Use Dataflow to continuously join the data and write results to BigQuery, then query BigQuery.

Answer

Use Cloud Functions to query both databases and return combined results.

Answer

Export both databases to Cloud Storage and use BigQuery federated queries.

Question 2

A company is using Cloud Bigtable for a high-throughput write workload. They notice periodic latency spikes. Which two metrics should they monitor to diagnose the issue? (Choose two.)

Accepted Answer

Error count. Request latency directly measures performance. Error count indicates failures or throttling. CPU utilization and disk usage are less direct indicators for write spikes. However, the question asks for two metrics to diagnose latency spikes; the most relevant are request latency and error count.

Answer

Disk bytes used

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Network throughput

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CPU utilization

Question 3

A company uses Cloud SQL for MySQL and wants to achieve high availability with automatic failover across zones while minimizing data loss. Which configuration should they use?

Accepted Answer

Configure a regional Cloud SQL instance with automatic failover. A regional Cloud SQL instance with automatic failover provides synchronous replication of data between two zones within the same region, ensuring zero data loss (RPO=0) and automatic failover with minimal downtime (RTO typically under 60 seconds). This meets the requirement for high availability with automatic failover across zones while minimizing data loss.

Answer

Enable read replicas in different zones

Answer

Use external read replicas with a failover script

Answer

Use Cloud SQL Enterprise Plus edition

Answer

Enable point-in-time recovery

Question 4

A multi-region application uses Cloud Spanner. The team needs to ensure that a write is immediately visible to all subsequent reads, even those performed in different regions. Which consistency mode should they use?

Accepted Answer

Strong consistency. Strong consistency (D) ensures that once a write is acknowledged, any subsequent read, regardless of region, will reflect that write. Cloud Spanner uses the TrueTime API and Paxos-based replication to provide external consistency (a form of strong consistency) across regions, making it the correct choice for immediate global visibility.

Answer

Eventual consistency

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Global consistency

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Bounded staleness

Question 5

A developer notices that a Cloud Function is timing out after 60 seconds. The function makes an external API call that occasionally takes longer than the timeout. What is the best practice to handle this?

Accepted Answer

Increase the timeout for the specific Cloud Function to a higher value. Cloud Functions have a configurable timeout per function (up to 540 seconds for HTTP functions). Increasing the timeout for the specific function that makes the slow external API call directly addresses the timeout issue without affecting other functions or introducing unnecessary retry overhead. This is the most targeted and efficient solution.

Answer

Implement retry logic without changing the timeout

Answer

Increase the timeout for all Cloud Functions in the project

Answer

Decrease the timeout to fail fast and implement retry logic

Question 6

A database team is planning to migrate a 500 GB MySQL database to Cloud SQL. They require minimal downtime. Which Database Migration Service job type should they use?

Accepted Answer

Continuous migration job. Continuous migration job performs an initial full dump and then continuously replicates changes via CDC, allowing a near-zero downtime cutover by promoting the replica.

Answer

One-time migration job

Answer

Cloud SQL replication from external primary

Answer

Bulk export and import

Question 7

You want to configure Cloud SQL for MySQL with high availability (HA). The application requires that failover be automatic and that the failover replica is in a different zone within the same region. Which configuration should you use?

Accepted Answer

Enable the high availability option when creating the Cloud SQL instance. Enabling the high availability (HA) option when creating a Cloud SQL for MySQL instance automatically provisions a standby replica in a different zone within the same region. This configuration provides automatic failover without manual intervention, meeting the requirement for HA with zone-level redundancy.

Answer

Use Cloud SQL with a cross-region replica and configure failover with gcloud

Answer

Set up a Cloud SQL instance with multiple read replicas and use failover via the Cloud SQL Proxy

Answer

Create a read replica in a different zone and configure automatic failover using a load balancer

Question 8

You manage a global ecommerce platform using Cloud Spanner. You need to support a query that joins two tables on a foreign key relationship. The tables are parent and child in an interleaved table hierarchy. Which statement about performance is TRUE?

Accepted Answer

The join will be fast because interleaving stores child rows with the parent row in the same split. Cloud Spanner interleaved tables physically co-locate child rows with their parent row within the same split (and often the same tablet). This means a join on the interleaved foreign key can be executed with minimal cross-node communication, as the data needed for the join is stored together, resulting in very fast query performance.

Answer

Interleaved tables cannot be joined

Answer

The join will be slow because interleaving increases split overhead

Answer

The join is only fast if you use a global secondary index

Question 9

A company is migrating a MySQL 5.7 database to Cloud SQL for MySQL 8.0. Their application uses utf8 charset and GROUP BY with nonstandard behavior (e.g., missing expressions in SELECT list). After migration, they notice queries that previously ran now fail. What is the most likely cause?

Accepted Answer

ONLY_FULL_GROUP_BY SQL mode is enabled by default in MySQL 8.0.. MySQL 5.7 allowed GROUP BY with columns not in the SELECT list by default (ONLY_FULL_GROUP_BY was off), but MySQL 8.0 enables it by default. This change can cause queries to fail if they rely on the old behavior.

Answer

The caching_sha2_password plugin changed authentication.

Answer

JSON data type behavior changed in MySQL 8.0.

Answer

The utf8 charset is not supported in MySQL 8.0.

Question 10

A company is migrating from Snowflake to BigQuery. They have a large dataset with semi-structured data stored as VARIANT columns in Snowflake. How should they represent this data in BigQuery?

Accepted Answer

Store as ARRAY> (RECORD type) with nested fields.. Snowflake's VARIANT type is used for semi-structured data like JSON. BigQuery has the RECORD (STRUCT) and REPEATED modes for nested and repeated data, and supports JSON data type (in preview) or storing as a STRING. The best practice is to use the native RECORD type to represent the structure for query performance and ease of use.

Answer

Store as STRING and use JSON_EXTRACT functions.

Answer

Store as JSON data type and use JSON functions for queries.

Answer

Store as BYTES and handle encoding in application.