DBS-C01 Mock Exam 90 — 25 Questions

Question 1

A financial services company needs a relational database with high availability and automatic failover across three Availability Zones in us-east-1. The workload consists of OLTP transactions with occasional analytic queries. Which database solution meets these requirements?

Accepted Answer

Amazon Aurora MySQL with Multi-AZ deployment across 3 AZs. Amazon Aurora MySQL with Multi-AZ deployment across 3 AZs meets the requirements because Aurora automatically replicates your data six ways across three Availability Zones, with a primary DB instance in one AZ and two read replicas in the other two AZs. In the event of a failure, Aurora automatically fails over to a read replica in under 30 seconds without data loss, providing high availability and automatic failover across three AZs. Aurora also supports both OLTP transactions and can handle occasional analytic queries via Aurora Replicas or Aurora Global Database for read scaling.

Answer

Amazon RDS for MySQL with Multi-AZ (2 AZs)

Answer

Amazon DynamoDB global tables

Answer

Amazon Redshift with cross-region snapshots

Question 2

A company is using Amazon DynamoDB to store session data for a web application. The session data expires after 24 hours. Which DynamoDB feature should the company use to automatically delete expired items?

Accepted Answer

DynamoDB Time to Live (TTL). DynamoDB Time to Live (TTL) is the correct choice because it provides a cost-effective, fully managed mechanism to automatically delete expired items based on a timestamp attribute in the table. TTL works by comparing the current time to the epoch time value stored in the designated TTL attribute; when the value is in the past, DynamoDB marks the item for deletion, typically within 48 hours. This eliminates the need for custom code or additional AWS services, directly addressing the requirement to remove session data after 24 hours.

Answer

A retention policy on the DynamoDB table

Answer

DynamoDB Streams

Answer

A scheduled AWS Lambda function that scans and deletes expired items

Question 3

Which TWO Amazon RDS features can be used to increase the availability of a production database?

Accepted Answer

Cross-Region read replicas with automatic promotion.. Option B is correct because cross-Region read replicas provide a secondary copy of the database in a different AWS Region, which can be manually promoted to a standalone primary instance in the event of a regional outage. This feature increases availability by enabling a disaster recovery strategy that goes beyond a single AWS Region, ensuring business continuity even if the entire primary Region becomes unavailable.

Answer

Enhanced Monitoring and Performance Insights.

Answer

Manual DB snapshot taken every hour.

Answer

Automated backups with a retention period of 35 days.

Question 4

A company's application is logging the error shown in the exhibit. The application is deployed on Amazon EC2 and connects to an Amazon RDS for MySQL Multi-AZ DB instance. Which configuration change is most likely to resolve this issue?

Accepted Answer

Increase the DB instance class to handle more concurrent connections.. The error log indicates that the application is hitting the maximum number of connections allowed by the RDS DB instance. Increasing the DB instance class (Option D) provides more memory and CPU resources, which allows the instance to support a higher `max_connections` value (calculated as `DBInstanceClassMemory / 12582880` for MySQL). This directly resolves the connection limit issue without changing the application's connection pool behavior or architecture.

Answer

Add an additional standby instance in a third Availability Zone.

Answer

Increase the connection pool timeout in the application configuration.

Answer

Create a read replica and direct write traffic to it.

Question 5

Refer to the exhibit. An IAM policy is attached to an IAM role used by a Lambda function that writes to a DynamoDB table. The function also needs to read items from the table. What is the outcome of this policy?

Accepted Answer

The Lambda function can write items but cannot read items. The IAM policy includes an explicit Deny for the `dynamodb:GetItem` action on the table, which overrides any Allow statements due to the explicit deny evaluation logic in AWS IAM. Since the Lambda function assumes a role with this policy, it is denied read access while the Allow for `dynamodb:PutItem` permits write operations. Therefore, the function can write but cannot read items from the DynamoDB table.

Answer

The policy is invalid because it contains both Allow and Deny for the same table

Answer

The Lambda function can both read and write items

Answer

The Lambda function cannot perform any operations on the table

Question 6

A social media application stores user posts in an Amazon RDS for PostgreSQL instance. The application experiences a sudden spike in read traffic during peak hours, causing database bottlenecks. The team needs to improve read scalability without changing the application code. Which solution is MOST cost-effective?

Accepted Answer

Use Amazon RDS for PostgreSQL Read Replicas. Option C is correct because Amazon RDS for PostgreSQL Read Replicas allow you to offload read traffic from the primary DB instance to one or more read-only replicas, improving read scalability without any application code changes. This is the most cost-effective solution as it leverages the existing PostgreSQL engine and requires only minimal additional compute and storage costs for the replicas.

Answer

Migrate to Amazon DynamoDB with DAX

Answer

Enable Multi-AZ on the RDS instance

Answer

Use Amazon ElastiCache to cache query results

Question 7

A company uses Amazon RDS for PostgreSQL to run a reporting application. The reporting queries are complex and take several minutes to complete, causing performance impact on the primary instance. The company wants to isolate the reporting workload without data staleness. Which solution should they implement?

Accepted Answer

Create a read replica and direct reporting queries to it.. Option D is correct because creating a read replica of the Amazon RDS for PostgreSQL primary instance allows you to offload complex reporting queries to the replica without impacting the primary. Read replicas use asynchronous replication (based on PostgreSQL streaming replication), which provides near-real-time data with minimal staleness, satisfying the requirement to isolate the reporting workload without significant data staleness.

Answer

Implement an Amazon ElastiCache cluster to cache query results.

Answer

Enable Multi-AZ and use the standby instance for reporting.

Answer

Take a manual snapshot of the database and restore it for reporting.

Question 8

A healthcare company stores patient records in Amazon DynamoDB. Each record includes a 'patient_id' (partition key) and 'visit_date' (sort key). The company needs to run ad-hoc queries to find all patients seen by a specific doctor within a date range. Which design approach minimizes cost and latency for this query pattern?

Accepted Answer

Create a global secondary index (GSI) with doctor_id as partition key and visit_date as sort key.. Option C is correct because a Global Secondary Index (GSI) with doctor_id as the partition key and visit_date as the sort key allows efficient key-based queries for all patients seen by a specific doctor within a date range. This avoids full table scans and filter operations, minimizing both cost (read capacity units) and latency. DynamoDB can directly retrieve the indexed items without scanning the base table.

Answer

Query the base table using a filter expression on doctor_id.

Answer

Create a local secondary index (LSI) with doctor_id as sort key.

Answer

Use a Scan operation with a filter expression for doctor_id and visit_date.

Question 9

An IAM policy is attached to a user to allow read access to the Orders table in DynamoDB. The user reports that a GetItem call for an order returns an 'AccessDeniedException'. What is the likely cause?

Accepted Answer

The user must specify a projection expression in the GetItem request to include only 'order_id' and 'status' attributes.. Option A is correct because when an IAM policy uses the `dynamodb:Attributes` condition key to restrict access to specific attributes (e.g., `order_id` and `status`), the user must include a `ProjectionExpression` in the `GetItem` request that explicitly lists only those allowed attributes. Without the projection expression, DynamoDB attempts to return all attributes, which triggers an `AccessDeniedException` because the policy denies access to attributes not listed in the condition.

Answer

The user does not have permissions to perform GetItem on the Orders table.

Answer

The resource ARN is incorrect; it should include the wildcard for the table.

Answer

The condition key 'dynamodb:Attributes' restricts access to only two attributes, but the user can still get all attributes.

Question 10

A company is designing a disaster recovery plan for an Amazon DynamoDB table that stores critical session data. The table is provisioned with on-demand capacity. The recovery objective is to have the data available in another AWS Region within 15 minutes of a regional outage. Which design should they choose?

Accepted Answer

Use DynamoDB Global Tables to replicate data across Regions.. Option C is correct because DynamoDB Global Tables provide multi-Region, fully replicated tables with automatic conflict resolution, enabling active-active replication that meets the 15-minute recovery objective without manual intervention. Global Tables replicate data across Regions in sub-second latency, ensuring data availability within the required RTO during a regional outage.

Answer

Use DynamoDB on-demand backups and restore to another Region.

Answer

Use DynamoDB Streams to replicate data to a table in another Region via AWS Lambda.

Answer

Create cross-Region Read Replicas for DynamoDB.

Question 11

A company is running an Oracle database on Amazon RDS with the configuration shown in the exhibit. The application is experiencing high latency for write operations. The storage is consistently showing high queue depth and write latency. Which change will most improve write performance?

Accepted Answer

Migrate to io1 or io2 storage with higher provisioned IOPS.. Option D is correct because migrating to io1 or io2 block storage with higher provisioned IOPS directly addresses the root cause of high queue depth and write latency. Unlike gp2, which has a baseline IOPS of 3 per GB (up to 16,000 IOPS at 5,334 GB) and a burst bucket that depletes under sustained load, io1/io2 provide consistent, provisioned IOPS independent of volume size. This ensures the storage subsystem can keep up with the write workload, reducing queue depth and latency.

Answer

Increase allocated storage to 1,000 GB to get higher gp2 baseline IOPS.

Answer

Enable storage auto scaling and increase storage throughput to 500 MB/s.

Answer

Change the DB instance class to db.r5.2xlarge.

Question 12

A company is designing a new application that requires a relational database with sub-millisecond read latency for a global user base. The workload is read-heavy with occasional writes. Which database solution should they choose?

Accepted Answer

Amazon Aurora with Auto Scaling. Amazon Aurora with Auto Scaling is the correct choice because it provides a relational database (MySQL/PostgreSQL-compatible) with sub-millisecond read latency via its distributed storage layer and read replicas. The read-heavy workload benefits from Aurora's automatic scaling of read capacity, while occasional writes are efficiently handled by the cluster volume. Aurora's architecture decouples compute and storage, enabling fast failover and consistent performance for global users.

Answer

Amazon DynamoDB with DAX

Answer

Amazon RDS for MySQL with Multi-AZ

Answer

Amazon ElastiCache for Redis

Question 13

A company runs a time-series application that records sensor data every second. The data volume is 500 GB per month and grows continuously. They need to query the last 30 days of data frequently and older data rarely. Which database design is MOST appropriate?

Accepted Answer

Amazon Timestream. Amazon Timestream is purpose-built for time-series data, automatically storing recent data in memory for fast queries and moving older data to a cost-optimized store. This matches the workload of frequent queries on the last 30 days and rare queries on older data, with continuous growth at 500 GB/month.

Answer

Amazon RDS for PostgreSQL with partitioning

Answer

Amazon DynamoDB with TTL

Answer

Amazon S3 with Athena and partitioning

Question 14

Which THREE are factors to consider when choosing between Amazon RDS and Amazon DynamoDB? (Select THREE.)

Accepted Answer

Serverless capacity management. Option A is correct because Amazon RDS requires manual or auto-scaling of compute and storage capacity, while DynamoDB offers serverless capacity management with on-demand mode that automatically scales throughput based on traffic. This is a key differentiator when deciding between provisioned capacity (RDS) and fully managed, pay-per-request scaling (DynamoDB).

Answer

Encryption at rest requirements

Answer

Need for in-memory caching

Question 15

Refer to the exhibit. An IAM policy is attached to a role used by an application that accesses the DynamoDB 'Orders' table. The application needs to perform a Scan operation on the table. According to the policy, is the Scan operation allowed?

Accepted Answer

Yes, because the policy explicitly allows Scan. The IAM policy includes an explicit Allow statement for the `dynamodb:Scan` action on the `Orders` table. In IAM policy evaluation logic, an explicit Allow overrides any default implicit Deny, and the Deny statement in the policy only blocks actions that match its `NotAction` element, which does not include Scan. Therefore, the Scan operation is allowed.

Answer

Yes, but only if the scan uses a filter expression

Answer

No, because the Deny statement blocks all actions

Answer

No, because the policy does not specify a condition

Question 16

A company is designing a database for a global e-commerce platform that requires low-latency reads and writes across multiple AWS Regions. The database must support strongly consistent reads and provide automatic failover. Which AWS service should the company use?

Accepted Answer

Amazon DynamoDB global tables. Amazon DynamoDB global tables provide a fully managed, multi-Region, multi-active database solution that delivers low-latency reads and writes across AWS Regions. It supports strongly consistent reads when using the same-Region endpoint and offers automatic failover by allowing any Region to handle writes independently, ensuring high availability without manual intervention.

Answer

Amazon ElastiCache for Redis global datastore

Answer

Amazon S3 with cross-region replication

Answer

Amazon Aurora Global Database

Question 17

Refer to the exhibit. A CloudFormation template creates a DynamoDB table. The application team needs to query orders by customer ID (which is not a key attribute). Which change to the template would enable efficient querying by customer ID?

Accepted Answer

Add a GlobalSecondaryIndex with CustomerID as the hash key and OrderDate as the range key. Option C is correct because a GlobalSecondaryIndex (GSI) allows querying on a non-key attribute (CustomerID) with a different key schema than the base table. By specifying CustomerID as the hash key and OrderDate as the range key, the application can efficiently query orders by CustomerID and optionally sort by OrderDate, without affecting the base table's primary key structure.

Answer

Change the KeySchema to use CustomerID as the hash key

Answer

Add a LocalSecondaryIndex on CustomerID

Answer

Enable DynamoDB Streams and use Lambda to populate a separate table

Question 18

A company runs a time-series application on Amazon RDS for PostgreSQL. The table 'events' has 500 million rows and is queried by event_time and event_type. Queries for the last hour are slow despite indexing. Which design change would most improve query performance?

Accepted Answer

Partition the table by month using PostgreSQL declarative partitioning. Option B is correct because partitioning the 'events' table by month using PostgreSQL declarative partitioning allows the query planner to prune partitions that do not contain data for the last hour. This dramatically reduces the number of rows scanned, even with a large table of 500 million rows, and directly addresses the slow query performance for time-range queries. Indexing alone cannot overcome the overhead of scanning a massive monolithic table for a narrow time window.

Answer

Add a composite index on (event_type, event_time)

Answer

Migrate to Amazon DynamoDB with TTL

Answer

Upgrade to a larger RDS instance

Question 19

Which TWO of the following are valid design considerations when using Amazon DynamoDB for a high-traffic e-commerce application? (Select TWO.)

Accepted Answer

Use atomic counters to maintain inventory counts. Option C is correct because atomic counters in DynamoDB allow you to increment or decrement a numeric attribute atomically using the UpdateItem operation with an UpdateExpression like 'SET inventory = inventory - :qty'. This is ideal for maintaining inventory counts in a high-traffic e-commerce application, as it avoids the need for read-modify-write cycles and reduces the risk of race conditions without consuming additional read capacity.

Answer

Use scan operations for frequent queries to reduce provisioned capacity

Answer

Use DynamoDB transactions to reduce read capacity consumption

Answer

Always use strongly consistent reads for all queries

Question 20

A company is migrating a MySQL database from on-premises to Amazon RDS for MySQL. The current database has several stored procedures and triggers that use user-defined functions (UDFs) compiled as shared libraries. What is the best practice for handling these UDFs in RDS?

Accepted Answer

Refactor the stored procedures to avoid using the custom UDFs.. Amazon RDS for MySQL does not allow access to the underlying file system, so you cannot upload custom UDF shared libraries (.so files). The best practice is to refactor the stored procedures and triggers to remove dependencies on these UDFs, replacing their logic with native MySQL functions or application-level code. This ensures compatibility with the managed RDS environment without requiring custom binaries.

Answer

Use Amazon RDS Custom for MySQL to upload the UDF libraries.

Answer

Use AWS Lambda to replace the UDFs.

Answer

Migrate to Amazon Aurora MySQL, which supports custom UDFs.