PCDE Practice Test 10 — 10 Questions

Question 1

Refer to the exhibit. You restored a Spanner database from a backup and are checking the status of the optimize operation. The operation has been running for 15 minutes and is 45% complete. The database is already accessible but queries on it are slower than expected. What should you do?

Accepted Answer

Continue running queries; performance will improve once the optimize operation completes.. Option A is correct because Spanner's optimize operation runs asynchronously and does not block database access. Queries are slower during optimization because the operation reorganizes data and rebuilds indexes, which consumes I/O and CPU resources. Once the optimize operation completes, query performance will improve as the data layout becomes more efficient.

Answer

Wait for the operation to finish before allowing any queries.

Answer

Drop and restore the database again to start fresh.

Answer

Cancel the optimize operation to reduce resource usage.

Question 2

You are a database engineer for an e-commerce platform running on Cloud SQL for PostgreSQL. The application team reports that a critical report query taking 5 seconds last week now takes over 30 seconds. The database CPU usage has increased from 40% to 85%. The query plan shows a sequential scan on the orders table. Which action should you take first to diagnose the problem?

Accepted Answer

Enable pg_stat_statements and check the query's execution statistics.. Option D is correct because enabling pg_stat_statements provides detailed execution statistics (e.g., total time, calls, rows, I/O) for each query, allowing you to identify the root cause of the performance regression without making speculative changes. Since the query plan shows a sequential scan and CPU is high, pg_stat_statements can reveal if the query is now reading more rows due to data growth or plan changes, guiding the next action (e.g., adding an index or tuning parameters).

Answer

Migrate the database to Cloud Spanner for better scaling.

Answer

Add a composite index on the orders table based on the query's WHERE clause.

Answer

Increase the machine type to add more vCPUs.

Question 3

Refer to the exhibit. Given the table definition and two queries, which statement about query performance is correct?

Accepted Answer

Query 1 will scan less data than Query 2 because it uses both partition pruning and clustering.. Query 1 uses both partition pruning (filtering on the partition key `event_date`) and clustering (filtering on the clustering column `user_id`), allowing it to skip irrelevant partitions and scan only the specific rows within the target partition. Query 2 uses only partition pruning on `event_date` but lacks a clustering filter, so it must scan all rows in the partition. Therefore, Query 1 scans less data than Query 2.

Answer

Query 2 will scan less data than Query 1 because it only needs to read one partition.

Answer

Query 1 will scan the same amount of data as Query 2 because both use partition pruning.

Answer

Both queries will perform a full table scan because the table is partitioned.

Question 4

A financial services company needs to design a BigQuery data model for real-time fraud detection. Data arrives from multiple streaming sources and must be joined with historical customer profiles (10 TB) and transaction lookup tables (500 GB). Which TWO design considerations are most important to minimize query latency and cost?

Accepted Answer

Use time-based partitioning on the historical customer table and cluster on customer_id.. Option A is correct because time-based partitioning on the historical customer table (10 TB) allows BigQuery to prune irrelevant partitions during queries, reducing the amount of data scanned and thus lowering cost and latency. Clustering on customer_id further optimizes joins with streaming data by colocating related rows, minimizing shuffle overhead.

Answer

Schedule a nightly script to recluster tables based on query patterns.

Answer

Use a single table for all streaming data without partitioning to avoid partition management overhead.

Answer

Denormalize all historical and lookup data into a single wide table.

Question 5

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 6

A company runs a critical application on Cloud SQL for PostgreSQL. The database engineer needs to ensure that if the primary instance fails, a standby instance in a different region can take over with minimal data loss. Which configuration should the Database Engineer implement?

Accepted Answer

Create a cross-region replica with asynchronous replication and manually promote it during a disaster.. Option C is correct because Cloud SQL for PostgreSQL supports cross-region replicas with asynchronous replication, which allows a standby instance in a different region to be promoted manually during a disaster. This minimizes data loss by replicating changes asynchronously, though some transactions may be lost if the primary fails before replication completes. Automatic failover is not supported for cross-region replicas in Cloud SQL, so manual promotion is required.

Answer

Set up a second Cloud SQL instance and configure application-level dual-writes to both instances.

Answer

Configure high availability (HA) within the same region using a regional persistent disk.

Answer

Create a cross-region replica with synchronous replication and enable automatic failover.

Question 7

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 8

Your team uses Cloud SQL for PostgreSQL and needs to run a one-time data correction query that will update 10 million rows. The instance has 8 vCPUs and 30 GB memory. The query is currently running for hours and impacting production performance. What should you do?

Accepted Answer

Create a clone of the instance, run the update on the clone, then promote it.. Option B is correct because creating a clone of the Cloud SQL instance provides an isolated environment where the heavy UPDATE can run without impacting production performance. After the update completes on the clone, you can promote it to become the new primary instance, effectively applying the data correction with minimal downtime. This approach avoids the performance degradation caused by running the query on the production instance and leverages Cloud SQL's cloning feature for a one-time data correction.

Answer

Create a read replica and run the update on the replica.

Answer

Run the query during off-peak hours with reduced concurrency.

Answer

Increase the instance size to 16 vCPUs and 60 GB memory before running the query.

Question 9

A company is migrating an on-premises PostgreSQL database to Cloud SQL. The database is 2 TB and must have minimal downtime during migration. Which migration strategy should the Database Engineer recommend?

Accepted Answer

Use Database Migration Service to set up continuous replication from the on-premises database to Cloud SQL, then perform a minimal-downtime cutover.. Option C is correct because the Database Migration Service (DMS) supports continuous replication from an on-premises PostgreSQL database to Cloud SQL using logical replication (pglogical or native PostgreSQL logical replication). This allows the source database to remain operational during the migration, and the cutover to Cloud SQL can be performed with minimal downtime, typically seconds to minutes, meeting the 2 TB size and low-downtime requirements.

Answer

Export the database using pg_dump and import into Cloud SQL using pg_restore during a maintenance window.

Answer

Set up PostgreSQL on Compute Engine and replicate data, then switch over to Cloud SQL.

Answer

Use Cloud SQL's built-in replication feature to connect directly to the on-premises database.

Question 10

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.

PCDE Practice Test 10 — 10 Questions

Exhibit

PCDE Practice Test 10 — 10 Questions

Exhibit