PCDE Plan and manage database infrastructure — 10 Questions

Question 1

A company runs a production Cloud SQL for PostgreSQL instance used by a web application. The instance experiences intermittent latency spikes during peak hours. You need to diagnose the cause without downtime. Which tool should you use first?

Accepted Answer

Use Cloud SQL Insights to analyze query performance and identify slow queries.. Cloud SQL Insights provides built-in query performance monitoring and diagnostics without requiring any downtime. It surfaces slow queries, lock contention, and resource bottlenecks directly from the PostgreSQL engine, making it the ideal first step to identify the root cause of intermittent latency spikes during peak hours.

Answer

Use Database Migration Service to failover to a read replica.

Answer

Use gcloud sql instances describe to check instance configuration.

Answer

Use VPC Flow Logs to analyze network traffic.

Question 2

A company is migrating an on-premises Oracle database to Cloud SQL for PostgreSQL. The database is 2 TB in size and the network bandwidth to Google Cloud is limited to 500 Mbps. The migration window is 48 hours. Which migration strategy should the Database Engineer recommend?

Accepted Answer

Export the database to flat files, compress, upload to Cloud Storage, then import to Cloud SQL.. Option C is correct because the 2 TB database size and 500 Mbps bandwidth yield a theoretical transfer time of approximately 9.5 hours (2 TB * 1024 GB/TB * 8 bits/byte / 500 Mbps / 3600 seconds/hour), which fits within the 48-hour window. However, pg_dump/pg_restore over a VPN (Option A) would be slower due to TCP overhead and latency, and Database Migration Service with continuous replication (Option B) requires ongoing connectivity and may not complete the initial load within the window. Exporting to flat files, compressing them (e.g., with gzip), uploading to Cloud Storage, and then importing to Cloud SQL leverages high-throughput parallel uploads and avoids network latency issues, making it the most reliable strategy for a one-time migration within the given constraints.

Answer

Create a VPN tunnel and use pg_dump/pg_restore over the network.

Answer

Use Database Migration Service with continuous replication.

Answer

Request a dedicated interconnect and then migrate.

Question 3

A financial services company uses Cloud Spanner for transaction processing. They need to ensure zero downtime during a schema change that adds a new column with a default value to a large table. Which approach should the Database Engineer take?

Accepted Answer

Use ALTER TABLE to add the column; Spanner handles schema changes online.. Option D is correct because Cloud Spanner supports online schema changes, including adding columns with default values, without requiring a maintenance window or causing downtime. Spanner applies schema updates asynchronously across all nodes while the database remains fully available for reads and writes, making it the ideal approach for zero-downtime requirements.

Answer

Create a new table with the new column, then use a fan-out pattern to write to both tables until the old table is deprecated.

Answer

Use an ALTER TABLE statement during a maintenance window.

Answer

Drop the table and recreate it with the new schema.

Question 4

A company runs a BigQuery data warehouse. They notice that query performance has degraded over time. The data is loaded daily from Cloud Storage using batch loads. Which action is most likely to improve query performance?

Accepted Answer

Partition and cluster tables based on common query filters.. Partitioning and clustering tables based on common query filters directly reduces the amount of data scanned per query by organizing data into physical segments. In BigQuery, this allows the query engine to prune entire partitions and clusters, significantly lowering I/O and improving performance without additional cost or complexity.

Answer

Increase the number of slots in the reservation.

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Create materialized views for all frequent queries.

Answer

Migrate the data to Cloud SQL for better performance.

Question 5

A gaming company uses Memorystore for Redis to cache player session data. They need to ensure high availability with automatic failover in case of a zone failure. Which configuration should the Database Engineer choose?

Accepted Answer

Deploy a Standard tier Redis instance with replication across two zones.. Memorystore for Redis Standard tier provides cross-zone replication with automatic failover, ensuring high availability during a zone failure. The Standard tier uses a primary and replica instance in different zones, and if the primary fails, the replica is automatically promoted. This meets the requirement for automatic failover without manual intervention.

Answer

Deploy a Basic tier Redis instance with multiple read replicas.

Answer

Deploy a Memcached cluster with multiple nodes.

Answer

Deploy a Basic tier Redis instance in a single zone.

Question 6

A company is designing a global application using Cloud Spanner. They need to ensure low latency reads and writes across three continents. Which TWO configurations should they consider?

Accepted Answer

Use a multi-region configuration with leader regions in each continent.. Option A is correct because Cloud Spanner multi-region configurations allow you to place leader regions in multiple continents, which enables low-latency strongly consistent reads and writes by directing traffic to the nearest leader. This is achieved through Spanner's TrueTime and Paxos-based replication, ensuring global consistency without sacrificing performance.

Answer

Use a single-region instance and rely on application caching.

Answer

Use strongly consistent reads from a single region.

Answer

Use interleaved tables to optimize query performance.

Question 7

A company is migrating their on-premises MySQL database to Cloud SQL. The database is 500 GB and they have a 1 Gbps network connection. They want to minimize downtime. Which THREE steps should they take?

Accepted Answer

Perform a test migration to validate the process.. Option A is correct because performing a test migration validates the entire process, including schema compatibility, data integrity, and application connectivity, before the actual cutover. This reduces the risk of unexpected failures during the production migration, which is critical for minimizing downtime. A test migration also helps estimate the time required for the final cutover and allows for tuning of the Database Migration Service settings.

Answer

Export the database to a SQL file and import after the cutover.

Answer

Schedule a maintenance window for the cutover.

Question 8

Your company runs a critical PostgreSQL database on Cloud SQL. You need to minimize downtime during a schema migration that could take up to 30 minutes. What should you do?

Accepted Answer

Create a clone of the instance, perform the migration on the clone, then promote the clone.. Option B is correct because creating a clone of the Cloud SQL instance allows you to perform the schema migration on an isolated copy without affecting the production database. Once the migration is complete and verified, you can promote the clone to take over as the primary instance, minimizing downtime to just the brief promotion switchover (typically seconds). This approach avoids the long 30-minute migration window on the live database.

Answer

Use Database Migration Service to migrate to a new instance during the migration window.

Answer

Configure a high-availability instance and perform the migration during a planned failover.

Answer

Add a read replica, perform the migration on the replica, then promote it.

Question 9

Your team is migrating a 5 TB MySQL database from on-premises to Cloud SQL. The database receives 2,000 writes per second and the network link has 500 Mbps bandwidth. You need to minimize migration time with zero data loss. What should you do?

Accepted Answer

Configure Database Migration Service with a connectivity test and start continuous replication.. Database Migration Service (DMS) with continuous replication is the correct choice because it supports live migration with minimal downtime and zero data loss for large databases like 5 TB. DMS uses MySQL binlog-based replication to synchronize changes from the on-premises source to Cloud SQL while the source remains operational, then performs a cutover with only seconds of downtime. This approach handles the 2,000 writes/second load and 500 Mbps bandwidth efficiently by streaming incremental changes rather than transferring the entire 5 TB in one shot.

Answer

Export the database using mysqldump and import into Cloud SQL using the console.

Answer

Use gcloud sql import with a compressed CSV export from on-premises.

Answer

Set up a VPN, then use mysqldump with --master-data and pipe to mysql on Cloud SQL.

Question 10

Your organization requires that all database backups be stored in a different region for disaster recovery. You are using Cloud SQL for MySQL. What backup configuration should you use?

Accepted Answer

Enable automated backups and select a different region for the backup location.. Cloud SQL for MySQL allows you to specify a different region for automated backup storage, which satisfies the disaster recovery requirement of storing backups in a separate region. By selecting a different region for the backup location, you ensure that if the primary region fails, the backups remain accessible for recovery. This is the only built-in option that directly meets the cross-region backup requirement without additional manual steps.

Answer

Enable automated backups and select the same region as the instance.

Answer

Use on-demand exports to Cloud Storage in the same region.

Answer

Configure a multi-region Cloud Storage bucket and point automated backups there.