PCDE Practice Test 24 — 15 Questions

Question 1

A site reliability engineer defines a service's availability SLI as the percentage of successful requests. Which of the following is the correct formula for this SLI?

Accepted Answer

good-request-count / valid-request-count * 100. An availability SLI defined as the percentage of successful requests is computed as good requests divided by valid requests, multiplied by 100. Valid requests exclude client-caused invalid requests (e.g., malformed requests that shouldn't count against availability). This matches the SRE convention where the denominator is the set of requests that should have succeeded.

Answer

good-request-count / total-requests (including invalid) * 100

Answer

error-request-count / valid-request-count * 100

Answer

valid-request-count / error-request-count * 100

Question 2

A DevOps engineer is setting up a new Google Cloud organization for their company. They need to ensure that all projects are created within a structured hierarchy that separates production, staging, development, and sandbox environments. Which folder structure BEST supports this requirement?

Accepted Answer

Create a folder for each environment (prod, staging, dev, sandbox) directly under the organization node. Within each environment folder, create subfolders for teams or products, and place projects in those subfolders.. Placing environment folders (prod, staging, dev, sandbox) directly under the organization node creates a clean policy boundary where IAM and org policies can be applied per environment — e.g., stricter controls on prod, looser on sandbox. Subfolders for teams or products within each environment allow granular delegation while preserving the environment isolation required for compliance and blast-radius containment.

Answer

Create a folder for each product under the organization node, and within each product folder, create subfolders for environments.

Answer

Create a flat folder structure under the organization node with one folder per team, and place all projects in their team folder regardless of environment.

Answer

Create a flat folder structure with one folder per project type (shared VPC, logging, security) and place all projects in those folders.

Question 3

What is the primary purpose of including a runbook URL in an alert policy's documentation?

Accepted Answer

To give responders immediate access to troubleshooting steps and escalation procedures. The runbook URL in an alert policy's documentation field provides responders with a direct link to the runbook, which contains step-by-step troubleshooting procedures, escalation paths, and remediation actions. This ensures that when an alert fires, the on-call engineer can quickly access the correct response plan, reducing mean time to resolution (MTTR).

Answer

To link to a dashboard that shows the alert's metric

Answer

To automatically trigger a Cloud Function when the alert fires

Answer

To provide a direct link to the source code repository

Question 4

A retail company uses Cloud SQL for PostgreSQL for inventory management. The schema has a table 'inventory' with columns: product_id, warehouse_id, quantity, last_updated. The table contains over 100 million rows. The application frequently runs aggregate queries to compute total quantity of a product across all warehouses (e.g., SELECT SUM(quantity) FROM inventory WHERE product_id = ?). These queries are slow, taking tens of seconds. The team tries a covering index on (product_id, quantity) but sees little improvement because they still need to scan many rows. They need to redesign the schema to improve aggregation performance. What is the best approach?

Accepted Answer

Create a summary table 'product_totals' with columns product_id and total_quantity, and use triggers to keep it updated on INSERT/UPDATE/DELETE in inventory.. A summary table precomputes the SUM(quantity) per product_id, so the aggregate query becomes a single-row lookup on a small table instead of scanning millions of inventory rows. Triggers on INSERT/UPDATE/DELETE keep the total_quantity synchronized with the base table, giving O(1) read performance for the aggregation pattern. This is the classic materialized-aggregate pattern for read-heavy OLTP workloads where the aggregation is expensive but the underlying data changes at a manageable rate.

Answer

Add a covering index on (product_id, quantity).

Answer

Migrate the inventory table to Cloud Spanner and use interleaved indexes.

Answer

Use BigQuery as a read replica and query there.

Question 5

A startup is building a mobile application and needs a real-time database that automatically scales to handle sudden spikes in user traffic. They want to minimise operational overhead and only pay for the resources they use. Which Google Cloud database should they choose?

Accepted Answer

Firestore. Firestore is a fully managed, serverless NoSQL document database that automatically scales horizontally to handle sudden traffic spikes without manual intervention. It offers real-time data synchronization via listeners, and its pay-per-use billing model aligns with the startup's requirement to minimize operational overhead and only pay for consumed resources.

Answer

Cloud Spanner

Answer

Cloud SQL

Answer

Cloud Bigtable

Question 6

A company is designing a schema for time-series sensor data in Cloud Spanner. They need to efficiently query the latest reading for each sensor. Which schema design is most appropriate?

Accepted Answer

Create a Sensors table and an interleaved Readings table with primary key (SensorId, Timestamp DESC). The most appropriate because it uses an interleaved Readings table under the Sensors table with the primary key (SensorId, Timestamp DESC). This allows efficient retrieval of the latest reading for each sensor by taking the first row per SensorId using the descending timestamp order. Interleaving ensures that rows for the same sensor are stored together, minimizing cross-node reads. Option A (single table with wide rows) leads to large rows and poor scalability. Option B (Cloud SQL) is not designed for high-throughput time-series data at scale. Option D (Bigtable) is a good choice for time-series but the question specifically requires using Cloud Spanner.

Answer

Use a single table with columns for each sensor and wide rows

Answer

Use Cloud SQL with a normalized schema

Answer

Use Cloud Bigtable with row keys (SensorId#Timestamp)

Question 7

You want to use OpenTelemetry Collector to send traces from an on-premises application to Cloud Trace. Which exporter should you configure in the Collector pipeline?

Accepted Answer

googlecloud. The OpenTelemetry Collector has an exporter 'googlecloud' (or 'googlecloudtrace') that sends traces to Cloud Trace. The 'logging' exporter writes to stdout, 'otlp' sends to an OTLP receiver, and 'prometheus' exports metrics. For Cloud Trace, the googlecloud exporter is correct.

Answer

logging

Answer

prometheus

Answer

otlp

Question 8

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.

Question 9

A company needs a fully managed, relational database with strong consistency and global distribution for a travel booking application that supports high concurrency and ACID transactions. Which Google Cloud database should they choose?

Accepted Answer

Cloud Spanner. Cloud Spanner is the correct choice because it is a fully managed, globally distributed relational database that provides strong consistency and ACID transactions across regions, making it ideal for high-concurrency travel booking applications that require global distribution and transactional integrity.

Answer

Cloud SQL

Answer

Cloud Bigtable

Answer

Firestore

Question 10

You are designing a distributed tracing strategy for a multi-service application deployed on Cloud Run and GKE. You need to ensure that all traces are captured with 100% sampling for the first 10 minutes after a new deployment, and then reduce to 10% sampling to control costs. Which approach should you use?

Accepted Answer

Use OpenTelemetry SDK with a custom sampler that checks the deployment timestamp stored in an environment variable, and send traces to the OpenTelemetry Collector configured to export to Cloud Trace.. A custom OpenTelemetry sampler is the only approach that can dynamically switch sampling rates based on deployment age. By reading a deployment timestamp from an environment variable, the sampler can apply 100% sampling for the first 10 minutes and then drop to 10%, while the Collector forwards spans to Cloud Trace. This gives full control over the sampling decision at the SDK level, which is exactly what the scenario requires.

Answer

Use Stackdriver Trace's automatic instrumentation on GKE and Cloud Run, and adjust the sampling rate via the Cloud Trace API after deployment.

Answer

Use Cloud Trace's built-in probabilistic sampler and configure it with 10% sampling in the configuration file.

Answer

Enable Cloud Trace on all services and use Cloud Monitoring alert on trace count to trigger a Cloud Function that changes the sampling rate.

Question 11

A team is migrating an on-premises PostgreSQL 13 database to AlloyDB using DMS continuous migration. During the CDC phase, the migration job shows an error: 'ERROR: could not start WAL streaming: ERROR: replication slots are not enabled on the source.' The source is running in Google Cloud Compute Engine. What is the most likely cause?

Accepted Answer

The source database parameter wal_level is set to 'replica' instead of 'logical'.. DMS continuous migration for PostgreSQL requires logical replication, which uses replication slots. The error indicates that the source database does not have the necessary configuration to support replication slots (wal_level=logical, max_replication_slots > 0).

Answer

The DMS connection profile uses the wrong public IP.

Answer

The source database is in read-only mode.

Answer

The source database does not have the pglogical extension installed.

Question 12

During an incident, the incident commander delegates tasks to multiple teams. After the incident is resolved, the team holds a postmortem. Which of the following is a key principle of a blameless postmortem culture?

Accepted Answer

Analyze contributing factors and implement action items with owners. Blameless postmortems focus on identifying system and process failures, not individual mistakes. The goal is to improve reliability.

Answer

Focus on human error and retraining

Answer

Identify the individual responsible and assign corrective action

Answer

Share the postmortem only with the incident commander

Question 13

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 14

An SRE team is designing an incident management process. Which TWO components are part of a typical incident command structure?

Accepted Answer

Incident Commander. In a typical incident command structure (modeled on ICS and used by Google SRE and others), the Incident Commander (option A) is the single decision-maker who owns the incident, sets priorities, and delegates tasks, so it is a core role. The Communications Lead (option D) is also a standard component, responsible for managing stakeholder and customer communications so the Incident Commander and responders can focus on mitigation. By contrast, a Developer (B) is a functional resource who may be called in to fix code but is not a defined incident command role, an On-call engineer (C) is the person paged to respond and may fill roles like Operations Lead but is not itself a command-structure component, and a Product Manager (E) is a business stakeholder who may be informed via the Communications Lead but is not part of the command structure.

Answer

Developer

Answer

On-call engineer

Answer

Product Manager

Question 15

A company is designing a data warehouse for business intelligence reporting. They want to organize data into fact and dimension tables to support fast aggregations. Which schema design is most appropriate for this purpose?

Accepted Answer

Star schema. The star schema is most appropriate for business intelligence reporting because it denormalizes dimension tables around a central fact table, enabling fast aggregations and simple queries. This design minimizes the number of joins required for analytical queries, which is critical for performance in OLAP workloads. In contrast, normalized schemas like 3NF or snowflake increase join complexity and degrade query speed.

Answer

Third Normal Form (3NF) schema

Answer

Snowflake schema

Answer

Entity-relationship schema