PCDE Practice Exam 67 — 20 Questions

Question 1

A company uses Cloud Logging and wants to receive real-time notifications when the number of 5xx errors exceeds 100 per minute. They need to set up an alerting policy. Which metric type and condition should they use?

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

Accepted Answer

Create a log-based counter metric and use a metric-threshold condition with rate alignment. A log-based counter metric can count errors per minute. The alert condition should be 'metric threshold' with 'CUMULATIVE' metric and 'rate' alignment to detect spikes.

Answer

Create a log-based counter metric and use a metric-absent condition

Answer

Use a Cloud Monitoring gauge metric with a custom value

Answer

Use a logs-based alert with a threshold on the log entry count

Question 2

A team is planning a migration from PostgreSQL to Cloud SQL with minimal downtime. They have set up DMS continuous migration. At cutover time, they need to ensure no data loss. What should they verify before promoting the destination?

Accepted Answer

The DMS replication lag is 0 seconds. Confirming DMS replication lag is 0 ensures all changes from the source have been applied to the destination. DMS status 'Running' is not enough. Source reads disabled would cause issues. DMS should be in a healthy state, but lag = 0 is the key.

Answer

The DMS job status is 'Running'

Answer

The destination has been promoted already

Answer

The source database is still accepting writes

Question 3

An engineer is tuning Cloud Spanner performance for a database that experiences high read latency on parent-child queries. The database schema uses a table for Users and a table for Orders with a foreign key on user_id. The Orders table has a secondary index on order_date. Which TWO actions can improve query performance? (Choose TWO)

Accepted Answer

Use the INTERLEAVE IN PARENT clause when creating the secondary index on order_date. Interleaving the Orders table in the Users table stores rows from both tables together on the same split, making parent-child joins much faster. Using INTERLEAVE IN PARENT for the secondary index on order_date stores the index data together with the base table, reducing lookup overhead. Adding a secondary index on user_id is unnecessary if Orders is interleaved in Users. Query explain plan is diagnostic, not a direct performance improvement. Increasing nodes increases throughput but not latency for individual queries.

Answer

Increase the number of Spanner nodes to reduce read latency

Answer

Add a secondary index on user_id in the Orders table

Answer

Run a query explain plan to identify bottlenecks

Question 4

A team is designing a Bigtable schema for a real-time fraud detection system. The row key includes device ID and timestamp. They need to avoid hotspotting during high write periods. Which two row key design patterns help achieve this? (Choose TWO.)

Accepted Answer

Add a hash prefix or salt to the beginning of the row key.. Adding a hash prefix or salt to the beginning of the row key distributes writes across multiple tablet servers, preventing hotspotting on a single node. In Bigtable, row keys are sorted lexicographically, so sequential device IDs or timestamps would cause all writes to hit the same tablet. A hash prefix ensures even distribution of write load.

Answer

Put the most frequently filtered fields first in the row key.

Answer

Use reverse timestamp to keep recent data first.

Answer

Use device ID as the sole row key prefix to group data by device.

Question 5

Your application uses Firestore for real-time updates. You notice increasing read latency during peak hours. The database is in Native mode with a single-location (us-central1). After reviewing metrics, you see that the number of document reads has not changed significantly, but the database size has grown. What is the most likely cause and solution?

Accepted Answer

Review and create composite indexes for common query patterns.. As the database size grows, Firestore's query performance can degrade if queries rely on automatic index scanning without composite indexes. Composite indexes allow Firestore to serve queries without scanning all documents, reducing read latency. The unchanged read count but increased latency indicates that queries are scanning more data due to missing indexes.

Answer

Enable multi-region replication to distribute read traffic.

Answer

The database needs to be defragmented periodically; run a compaction command.

Answer

Migrate the database to Datastore mode for better performance.

Question 6

A startup is using Cloud SQL for PostgreSQL and wants to minimize downtime during maintenance. The application can tolerate a few minutes of read-only mode. Which configuration should they use?

Accepted Answer

Use a read replica and promote it during maintenance.. Using a read replica and promoting it during maintenance allows the application to switch to a read-write capable instance with minimal downtime. The application can tolerate a few minutes of read-only mode, so the brief period when the replica is promoted and the original primary is unavailable is acceptable. This approach avoids the longer downtime associated with other methods like HA failover or simply waiting for maintenance to complete.

Answer

Enable automatic storage increase.

Answer

Configure a high availability (HA) instance with regional failover.

Answer

Schedule maintenance during off-peak hours only.

Question 7

A company is using Cloud SQL for PostgreSQL and needs to perform a disaster recovery drill by promoting a read replica to a standalone instance. They also need to ensure the replica is as current as possible before promotion. Which TWO steps should they take? (Choose two.)

Accepted Answer

Promote the replica using gcloud sql instances promote-replica. `gcloud sql instances promote-replica` is the standard command to promote a Cloud SQL read replica to a standalone instance, making it a primary that can accept writes. Option C is correct because checking the `replication_lag` metric ensures the replica has applied all pending changes from the primary before promotion, minimizing data loss. This step is critical because promoting a replica that is behind can result in lost transactions.

Answer

Enable binary logging on the replica

Answer

Create an on-demand backup of the primary before promotion

Answer

Force a failover to the replica

Question 8

A team runs a service on Google Kubernetes Engine (GKE) and wants to inject faults to test resilience. They need to introduce latency into requests to a specific microservice without modifying code. Which tool should they use?

Accepted Answer

Traffic Director with HTTP fault filter. Traffic Director can inject faults via HTTP fault filter for services using Istio or Traffic Director. Chaos Mesh on GKE can inject faults at the pod level. Since the requirement is to inject latency into requests between services without code changes, a service mesh with fault injection (like Istio with VirtualService) is ideal. Traffic Director supports fault injection via HTTP filters. Chaos Mesh can also inject latency by sidecar. Both are valid, but Traffic Director is specifically for traffic management. The question likely expects Traffic Director or Istio. Since Traffic Director is a GCP service, it might be the preferred answer. However, Chaos Mesh is also a common choice. I'll choose Traffic Director as it's integrated.

Answer

Cloud Endpoints

Answer

Cloud Armor

Answer

Cloud Load Balancing

Question 9

A company plans to migrate a MySQL database to Cloud SQL with minimal downtime. They use Database Migration Service with continuous CDC. After starting the migration, the initial full dump completes, and CDC replication begins. The application team needs to cut over during a maintenance window. What must the engineer do just before promoting the destination to ensure no data loss?

Accepted Answer

Quiesce writes to the source, confirm replication lag is zero, then promote the destination.. Before promoting the destination, the engineer must verify that the replication lag is zero, meaning all changes from the source have been applied to the destination. This ensures no data loss during cutover. After confirming zero lag, the source should be quiesced (writes stopped) to prevent further changes, then the destination can be promoted.

Answer

Promote the destination immediately; replication lag is automatically handled.

Answer

Take a manual snapshot of the source with mysqldump and import it to the destination.

Answer

Stop the migration job and delete the source database.

Question 10

A startup needs a fully managed relational database for their e-commerce platform with high availability, automatic failover, and read replicas. They expect moderate traffic and want to minimize operational overhead. Which Google Cloud service should they use?

Accepted Answer

Cloud SQL. Cloud SQL offers fully managed MySQL, PostgreSQL, and SQL Server with high availability and read replicas. It is the best fit for moderate-traffic OLTP workloads.

Answer

Cloud Spanner

Answer

Firestore

Answer

Bigtable

Question 11

A company runs a critical application on Cloud SQL for MySQL with an HA configuration. They want to test their disaster recovery plan without affecting production. They need to validate that a cross-region read replica can be promoted successfully in the event of a regional outage. Which approach should they take?

Accepted Answer

Create a clone of the cross-region read replica and promote the clone. To test DR without affecting production, you can promote a cross-region read replica to a standalone instance for testing. However, promoting a read replica stops replication and makes it a writable instance. To avoid impacting production, you should create a clone of the cross-region read replica and promote the clone. Alternatively, you can create a snapshot of the replica and restore to a new instance. The safest way is to create a clone from the replica and promote the clone.

Answer

Promote the cross-region read replica to a standalone instance, then re-create the replica after testing

Answer

Use point-in-time recovery to restore the primary to a new instance in the secondary region

Answer

Create a new read replica in the secondary region and promote that

Question 12

A Cloud Spanner database has a table with a primary key (UserId, Timestamp). Queries that filter by Timestamp range for a specific UserId are fast, but queries that filter only by Timestamp range across all users are slow. Which TWO improvements would help?

Accepted Answer

Use a leading column of the primary key that supports range scans.. In Cloud Spanner, the primary key order determines how data is physically sorted and stored. By making Timestamp the leading column of the primary key (e.g., (Timestamp, UserId)), range scans on Timestamp become efficient as Spanner can perform a contiguous scan of the sorted data. This directly addresses the slow queries that filter only by Timestamp range across all users.

Answer

Use a hash prefix on UserId.

Answer

Create an interleaved table structure.

Answer

Partition the table by Timestamp.

Question 13

A data analyst needs to create a reporting table that aggregates sales data by month. They want to ensure the table is optimized for querying by month and product category. Which table design best supports this?

Accepted Answer

Partition by month and cluster by product_category.. Partitioning by month physically separates data into monthly segments, allowing query pruning to skip irrelevant partitions when filtering by month. Clustering by product_category within each partition co-locates rows with the same category, reducing the amount of data scanned for queries that filter on both month and category. This design optimizes both I/O and scan efficiency for the described workload.

Answer

Use a table with clustering on product_category only.

Answer

Use a flat table with no partitioning.

Answer

Use a view that selects month and product_category.

Question 14

A company needs to perform real-time analytics on streaming data from IoT devices with millisecond latency for alerts, and also run complex historical analytics. Which Google Cloud database architecture supports both?

Accepted Answer

AlloyDB with columnar engine. AlloyDB with columnar engine handles real-time inserts and fast analytical queries on the same data, ideal for HTAP workloads.

Answer

Cloud Bigtable for real-time and BigQuery for analytics

Answer

Cloud SQL (read-only replica) for analytics

Answer

Cloud Spanner with interleaved tables

Question 15

A company wants to store and analyze time-series metrics from thousands of servers. The data is write-heavy with occasional reads of recent data. They need low-latency writes and the ability to scan large ranges later. Which Google Cloud database is MOST appropriate?

Accepted Answer

Cloud Bigtable. Bigtable is designed for time-series data, high write throughput, and efficient range scans. It can handle large volumes of time-series data with low latency.

Answer

Firestore

Answer

Cloud Spanner

Answer

Cloud SQL

Question 16

You are designing a Bigtable schema for a messaging application where users have conversations. Each row represents a message with row key 'userID#conversationID#timestamp'. The application queries the most recent messages for a given conversation. How should you modify the row key to optimize for this query pattern?

Accepted Answer

Reverse the timestamp. To get the most recent messages, you want to scan recent rows. If timestamp is increasing, the most recent messages have the highest timestamp but at the end of the scan range. By reversing the timestamp, you make recent messages appear first in a scan. Field promotion doesn't apply here. Salting would help writes but not the read pattern. The best approach is to reverse the timestamp so that most recent messages have lexicographically smaller keys.

Answer

Promote the conversationID before userID

Answer

Store timestamp as a column instead of part of row key

Answer

Use a hash prefix of the conversationID as the first part

Question 17

A team is designing a schema for Cloud Spanner to store user profiles. The primary access pattern is to read a user's profile by their unique user ID. To avoid write hotspots, which primary key design strategy should the team use?

Accepted Answer

Use a UUID (universally unique identifier) as the primary key. Monotonically increasing keys (e.g., sequential integers or timestamps) cause all writes to hit the same tablet, creating hotspots. Using a random UUID distributes writes evenly across the cluster, avoiding hotspots.

Answer

Use the user's email address as the primary key

Answer

Use a monotonically increasing integer as the primary key

Answer

Use a timestamp as the primary key

Question 18

A user runs the query above on a large table and receives an out-of-memory error. What is the most likely cause?

Accepted Answer

The ORDER BY clause forces sorting of the entire dataset in memory on a single worker. The ORDER BY clause in a distributed SQL engine like Snowflake or BigQuery forces all data to be sent to a single worker node for sorting, which can exceed the memory limit of that node when the dataset is large. This is a common cause of out-of-memory errors in MPP (Massively Parallel Processing) systems, as sorting is not a distributable operation by default without explicit partitioning or window functions.

Answer

The table is a materialized view that cannot handle ORDER BY

Answer

The query uses COUNT(*) without a GROUP BY

Answer

The table is not partitioned, so full table scan causes memory overflow

Question 19

A company is using Cloud Spanner and needs to add a new column to an existing table that has billions of rows. The column must have a default value of 0. The team is concerned about downtime. Which approach should they take to add the column with zero downtime?

Accepted Answer

Use ALTER TABLE ADD COLUMN with DEFAULT 0; the operation is online and non-blocking. Cloud Spanner supports online schema changes that are non-blocking. Adding a column with a DEFAULT value is an online operation that does not block reads or writes, and does not require copying data. The new column is added with the default value for existing rows at read time, not by backfilling.

Answer

Take the application offline, run ALTER TABLE to add the column, then bring the application back online

Answer

Create a new table with the column, copy data using Dataflow, then rename the tables

Answer

Add the column without a default, then run a batch update to set the default value

Question 20

A DevOps team uses Terraform Cloud to manage infrastructure. They want to enforce that all Terraform plans must pass a set of policy checks before they can be applied. The policies include restricting resource types and ensuring proper tagging. Which Terraform Cloud feature should they use?

Accepted Answer

Use Terraform Cloud's Sentinel policies.. Sentinel is Terraform Cloud's policy-as-code framework. It allows writing policies (in Sentinel language) that are evaluated during the plan phase. Policies can enforce constraints on resources and tags.

Answer

Use Terraform Cloud's Cost Estimation feature.

Answer

Use Terraform Cloud's Run Triggers to chain workspaces.

Answer

Use Terraform Cloud's API to run custom scripts after plan.