DBS-C01 Mock Exam 71 — 25 Questions

Question 1

A company uses Amazon DynamoDB to store user session data. The security team wants to ensure that all data is encrypted at rest using a customer managed key (CMK) in AWS KMS, and that they can audit key usage. They also want to minimize operational overhead. Which approach should they take?

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

Accepted Answer

Enable DynamoDB encryption at rest with a customer managed CMK in AWS KMS.. DynamoDB encryption at rest with a customer managed CMK allows the security team to use their own KMS key, audit key usage through CloudTrail, and manage key rotation. It is a server-side encryption feature that requires no application changes and minimal operational effort. The other options either do not use a CMK, add complexity, or are not supported.

Answer

Use AWS CloudHSM to store the encryption keys and integrate with DynamoDB.

Answer

Use client-side encryption with a custom application that encrypts data before writing to DynamoDB.

Answer

Enable DynamoDB encryption at rest with the default AWS owned CMK.

Question 2

A database specialist is troubleshooting an Amazon Aurora PostgreSQL DB cluster that is experiencing performance degradation. The cluster has one writer and one reader instance. The specialist observes that the writer's CPU utilization is consistently above 90%, while the reader's CPU is around 30%. The application performs a mix of read and write operations. The specialist wants to identify the cause of the high CPU on the writer. Which TWO actions should the specialist take to diagnose the issue? (Choose two.)

Accepted Answer

Review the PostgreSQL pg_stat_statements view on the writer instance to identify queries with high total execution time.. To diagnose high CPU on the Aurora PostgreSQL writer, the specialist should use tools that identify resource-intensive queries. Performance Insights provides a visual dashboard of database load by SQL statement, and pg_stat_statements offers detailed query execution statistics. Both directly reveal which queries are consuming the most CPU, enabling targeted optimization. Other options focus on replication, disk I/O, or connection errors, which are less relevant to the observed CPU issue.

Answer

Examine the Enhanced Monitoring metrics for the writer instance to check for high disk I/O wait.

Answer

Check the Aurora Replica lag metric to determine if the reader is falling behind.

Answer

Use Amazon CloudWatch Logs Insights to analyze the PostgreSQL error logs for frequent connection errors.

Question 3

A database specialist is monitoring an Amazon Aurora MySQL cluster with a writer and one reader. The application uses the reader endpoint for read-only queries. The specialist observes that the reader instance's ReplicaLag metric is consistently increasing and is currently at 300 seconds. The writer instance shows high write throughput. Which action should the specialist take to reduce the replica lag?

Accepted Answer

Modify the reader instance to a larger instance class to increase its capacity to apply changes.. The reader instance is likely unable to keep up with the write volume due to insufficient resources. Scaling up the reader instance provides more compute and memory to apply the replication stream faster, directly reducing replica lag. Other options either do not impact replication performance or are counterproductive.

Answer

Enable Multi-AZ on the writer instance to improve replication performance.

Answer

Increase the size of the Aurora cluster volume to provide more IOPS for replication.

Answer

Change the reader endpoint to route queries to the writer instance.

Question 4

A media company is building a new application to store and analyze time-series data from IoT sensors. The data volume is expected to grow to several terabytes per day, and queries will primarily filter by sensor ID and a time range. The company wants a fully managed, petabyte-scale data warehouse that supports SQL and integrates with existing BI tools. Which AWS service should the company use?

Accepted Answer

Amazon Redshift. Amazon Redshift is the correct choice because it is a fully managed, petabyte-scale data warehouse that supports SQL and integrates with BI tools. Its columnar storage and MPP architecture are designed for analytical queries on large datasets, making it ideal for time-series data filtered by sensor ID and time range.

Answer

Amazon ElastiCache for Redis

Answer

Amazon DynamoDB

Answer

Amazon RDS for PostgreSQL

Question 5

A company is using Amazon Neptune to store a graph database for a social networking application. The application requires complex traversals and real-time recommendations. The graph data is highly connected, with millions of vertices and edges. The company needs to ensure that queries perform well even as the graph grows. Which design approach should the company take to optimize Neptune performance?

Accepted Answer

Deploy Neptune with read replicas and distribute read queries across them.. Amazon Neptune supports read replicas to scale read queries. For a social networking application with complex traversals and real-time recommendations, the workload is likely read-heavy. Distributing read queries across multiple read replicas improves performance and allows the primary instance to handle writes. Vertical scaling has limits, and sharding is not natively supported. Query optimization is helpful but not a design approach. Therefore, deploying read replicas is the correct design approach.

Answer

Shard the graph data across multiple Neptune clusters based on vertex properties.

Answer

Use a single large instance and vertically scale as the graph grows.

Answer

Enable Neptune's query planner and use Gremlin traversal optimization techniques.

Question 6

A database specialist is managing an Amazon RDS for PostgreSQL DB instance that is experiencing performance issues. The specialist suspects that recent changes to the application are causing increased load. The specialist needs to identify the top SQL statements consuming the most time and resources. Which two actions should the specialist take to gather the necessary performance data? (Choose two.)

Accepted Answer

Enable Performance Insights on the DB instance and analyze the top SQL statements in the Performance Insights dashboard.. Performance Insights provides a user-friendly dashboard that highlights top SQL statements by load, while the pg_stat_statements extension offers detailed execution statistics directly within PostgreSQL. Both tools are designed to identify resource-intensive queries. Performance Insights requires no additional setup beyond enabling the feature, whereas pg_stat_statements must be enabled as an extension. Together, they give comprehensive SQL-level performance data.

Answer

Enable Enhanced Monitoring and review the process list to identify the top SQL statements.

Answer

Enable RDS log exports for PostgreSQL logs and parse the logs for slow queries.

Answer

Use AWS CloudTrail to log all API calls and analyze the SQL statements in the logs.

Question 7

A media company stores millions of video metadata records in Amazon DynamoDB. Each record has a partition key of videoId and a sort key of uploadTimestamp. The company frequently queries for all videos uploaded by a specific uploader within the last 30 days. The uploaderId is currently stored as a non-key attribute. Queries are becoming slow and expensive because they require a full table scan. Which change should a database specialist make to optimize these queries?

Accepted Answer

Create a global secondary index with uploaderId as the partition key and uploadTimestamp as the sort key.. The access pattern requires querying by uploaderId and filtering by uploadTimestamp. A global secondary index with uploaderId as the partition key and uploadTimestamp as the sort key enables efficient Query operations that return only the relevant items. This eliminates the full table scan, reduces latency, and lowers consumed read capacity. Other options either do not provide a direct query path or misconfigure the index type.

Answer

Enable DynamoDB Streams on the table and process the stream with AWS Lambda to build a separate query cache.

Answer

Create a local secondary index with uploaderId as the sort key.

Answer

Increase the read capacity units of the table to eliminate the performance issue.

Question 8

A media company stores millions of video metadata records in Amazon DynamoDB. Each record has a partition key of videoId and a sort key of uploadTimestamp. The team frequently queries for all videos uploaded by a specific creator within a date range. The creatorId is not part of the key schema. Queries currently scan the entire table and are slow and expensive. Which design change best improves query performance and reduces cost?

Accepted Answer

Create a global secondary index with partition key creatorId and sort key uploadTimestamp, and query that index.. The access pattern requires querying by creatorId and a range of uploadTimestamp, neither of which is the table's partition key. A global secondary index with creatorId as the partition key and uploadTimestamp as the sort key enables efficient, targeted queries. This avoids full table scans, lowers latency, and reduces consumed read capacity compared to scanning the base table.

Answer

Enable DynamoDB Streams and use a Lambda function to maintain a separate table keyed by creatorId.

Answer

Change the table's partition key to creatorId and the sort key to uploadTimestamp.

Answer

Add a local secondary index with creatorId as the sort key.

Question 9

A healthcare company runs an Amazon Aurora MySQL cluster that stores patient records. The compliance team requires that all data at rest be encrypted with a customer-managed AWS KMS key, and that the key be rotated annually. A database engineer notices that the cluster was created without encryption. What is the MOST operationally efficient way to meet the encryption requirement?

Accepted Answer

Create a new encrypted Aurora cluster from a snapshot of the unencrypted cluster, then update the application endpoint.. Aurora encryption must be enabled when the cluster is created; it cannot be turned on later. The supported way to encrypt an existing unencrypted Aurora database is to take a snapshot and restore it into a new cluster with a customer-managed KMS key, then repoint the application. This meets the compliance requirement with minimal data movement and no manual data export.

Answer

Enable encryption on each Aurora Replica individually, which will propagate to the writer instance.

Answer

Use AWS KMS to create a grant on the existing cluster's storage volume and rotate the key annually.

Answer

Modify the existing cluster to enable encryption and select the customer-managed KMS key.

Question 10

A database specialist needs to monitor the CPU utilization of an Amazon RDS for MySQL DB instance and receive an alert when it exceeds 80% for 5 minutes. Which AWS service should be used to set up this alarm?

Accepted Answer

Amazon CloudWatch. Amazon CloudWatch is the service for monitoring AWS resources and setting alarms. It collects metrics from RDS, including CPUUtilization, and can trigger alarms when conditions are met. You can create an alarm that sends a notification via Amazon SNS when CPU exceeds 80% for 5 minutes. Other services like CloudTrail, Trusted Advisor, and Performance Insights do not provide this alerting capability.

Answer

AWS CloudTrail

Answer

AWS Trusted Advisor

Answer

Amazon RDS Performance Insights

Question 11

A hospital wants to migrate a legacy patient-records application to Amazon Aurora PostgreSQL. The application uses the Oracle package DBMS_LOB and several Oracle-specific PL/SQL constructs. The migration team must assess compatibility before committing. Which action provides the MOST accurate compatibility assessment with the LEAST effort?

Accepted Answer

Run the AWS Schema Conversion Tool (AWS SCT) against the source Oracle schema and review the generated assessment report.. AWS Schema Conversion Tool is purpose-built to evaluate a source Oracle schema against an Aurora PostgreSQL target. Its assessment report quantifies conversion complexity and flags Oracle-specific packages and PL/SQL that require manual remediation, giving the migration team an accurate, low-effort compatibility picture before any data movement or code rewrite begins.

Answer

Export the Oracle schema with Data Pump and import it into a new Aurora PostgreSQL cluster using the aws_s3 extension.

Answer

Use AWS Database Migration Service (AWS DMS) with the Oracle-to-PostgreSQL engine to perform a full load and compare row counts.

Answer

Enable Oracle Active Data Guard and replicate the schema to an Amazon RDS for Oracle read replica for testing.

Question 12

A financial services firm runs an Amazon RDS for Oracle database with a primary instance and a read replica. The application performs heavy read operations during business hours and requires minimal latency. The team wants to ensure that read queries are distributed across the primary and the read replica to balance the load. Which approach should they use?

Accepted Answer

Implement application-level load balancing by directing a percentage of read queries to the primary and the rest to the read replica.. RDS for Oracle does not offer a native load balancing mechanism across a primary and read replica. The only way to distribute read queries across both is to implement application-level logic that splits reads between the two endpoints. This allows the team to balance load, handle replication lag, and maintain minimal latency, unlike DNS round-robin or Multi-AZ, which do not serve this purpose.

Answer

Configure the application to use a custom DNS endpoint that round-robins between the primary and read replica.

Answer

Use the RDS read replica endpoint for read-only queries and the primary endpoint for writes.

Answer

Enable Multi-AZ for the RDS instance to automatically distribute read traffic across Availability Zones.

Question 13

A logistics company is migrating an on-premises MongoDB 4.4 replica set to Amazon DocumentDB. The dataset is 800 GB and the company requires the cutover to complete with less than five minutes of application downtime. The source database can accept a brief read-only period. Which migration approach should the team use?

Accepted Answer

Use the AWS DMS MongoDB source endpoint with change data capture to continuously replicate to DocumentDB, then stop writes and wait for replication to catch up before cutover.. AWS DMS can read the MongoDB oplog to capture ongoing changes and apply them to Amazon DocumentDB, so the bulk of the 800 GB is replicated ahead of the cutover. Pausing writes briefly lets the remaining changes drain, enabling cutover within the five-minute downtime target.

Answer

Configure the on-premises MongoDB replica set to add the DocumentDB cluster as a member node and let normal replication synchronize the data.

Answer

Restore a MongoDB snapshot into Amazon S3 and use AWS Glue to load the collection data into DocumentDB.

Answer

Use mongodump and mongorestore against the DocumentDB cluster endpoint during the cutover window.

Question 14

A database specialist manages an Amazon RDS for PostgreSQL DB instance that is encrypted with an AWS KMS customer managed key. A security policy requires that the key be rotated annually. The specialist rotates the KMS key. What is the effect on the existing RDS instance and its encrypted data?

Accepted Answer

Existing data remains readable because KMS retains the old key material to decrypt it, while new writes are protected by the new key material.. KMS key rotation creates new cryptographic material while preserving prior material for decryption, so data encrypted before rotation stays readable and new data keys use the new material. RDS requires no restore or re-encryption, and the instance remains available. Snapshots taken before rotation are still restorable because the old material is retained.

Answer

The DB instance becomes inaccessible until it is restored from a snapshot taken after the rotation.

Answer

The rotation deletes the previous key material immediately, making previously encrypted snapshots permanently unrecoverable.

Answer

All existing data must be re-encrypted by restoring from a snapshot and re-importing it under the new key version.

Question 15

A company is migrating a 1 TB MySQL database from an on-premises data center to Amazon Aurora MySQL. The migration must be completed with minimal downtime, and the team wants to use AWS DMS for ongoing replication. After the initial load, they notice that some tables are not replicating changes. The DMS task logs show errors related to binary logging. Which action should the team take to resolve the issue?

Accepted Answer

Set the source MySQL parameter binlog_format to ROW and ensure binlog_row_image is set to FULL. AWS DMS requires MySQL sources to use row-based binary logging (binlog_format=ROW) and binlog_row_image=FULL for change data capture. Without these settings, DMS cannot capture the necessary before and after images for updates and deletes, leading to replication errors. Correcting the binary logging format resolves the issue and allows ongoing replication to proceed.

Answer

Enable GTID-based replication on the source MySQL instance

Answer

Set the source MySQL parameter binlog_format to STATEMENT

Answer

Increase the value of max_binlog_size on the source MySQL instance

Question 16

A financial services company uses Amazon DynamoDB to store sensitive customer transaction data. The security team wants to ensure that all data written to the table is encrypted using a customer managed key in AWS KMS, and that they can audit key usage. Which configuration should they implement?

Accepted Answer

Enable DynamoDB encryption at rest using a customer managed key in AWS KMS.. To meet the requirement of encryption at rest with a customer managed key and auditability, the company should configure DynamoDB to use a customer managed key in AWS KMS. This allows them to control key policies, audit usage via CloudTrail, and rotate the key as needed, all without application changes.

Answer

Enable DynamoDB encryption at rest using an AWS owned key.

Answer

Enable DynamoDB encryption at rest using an AWS managed key (aws/dynamodb).

Answer

Enable client-side encryption using the Amazon DynamoDB Encryption Client with a key stored in AWS Secrets Manager.

Question 17

A company is planning to migrate a large on-premises MySQL database to Amazon Aurora MySQL. The database is 10 TB in size and the company wants to minimize downtime during the migration. They decide to use AWS Database Migration Service (AWS DMS) with a full load plus change data capture (CDC). Which of the following must be configured on the source MySQL database to support CDC?

Accepted Answer

Enable binary logging and set the binlog_format parameter to ROW.. AWS DMS uses the MySQL binary log to capture ongoing changes for CDC. The binary log must be enabled, and the binlog_format must be set to ROW so that DMS can read row-level changes. This is a prerequisite for CDC tasks. Without these settings, the CDC phase will fail or not capture changes.

Answer

Set the transaction isolation level to READ COMMITTED.

Answer

Enable the general query log to capture all SQL statements.

Answer

Enable the slow query log and set long_query_time to 0.

Question 18

A healthcare provider is designing a new patient records system on AWS. Regulatory requirements mandate that the primary database be deployed in a single AWS Region with synchronous replication to a standby that can take over automatically within minutes, and that no data leave the Region. The team wants to minimize operational effort for failover. Which design should the team choose?

Accepted Answer

Amazon RDS for PostgreSQL with a Multi-AZ DB instance deployment. The requirements combine single-Region data residency, synchronous replication to a standby, and automatic failover with minimal operational effort. An Amazon RDS Multi-AZ DB instance deployment delivers exactly that: a synchronous standby in a second Availability Zone, managed failover through DNS endpoint repointing, and no data leaving the Region.

Answer

Amazon DynamoDB global tables with automatic multi-Region replication

Answer

Amazon RDS for PostgreSQL with a cross-Region read replica and manual promotion

Answer

Amazon Aurora Global Database with a secondary Region for failover

Question 19

A small startup is building a content management system that stores articles as JSON documents. The documents have varying schemas, and the team wants to query nested fields without defining a rigid table structure. They expect moderate traffic and want a fully managed document database on AWS. Which service should they use?

Accepted Answer

Amazon DocumentDB (with MongoDB compatibility). The requirement is a fully managed document database that supports flexible schemas and nested field queries. Amazon DocumentDB provides MongoDB-compatible document storage and querying, making it ideal for a content management system with varying article structures. Relational, key-value, and graph databases either impose rigid schemas, require complex access-pattern design, or are optimized for different data models.

Answer

Amazon RDS for MySQL with a JSON column type

Answer

Amazon Neptune with RDF triples

Answer

Amazon DynamoDB with a single-table design

Question 20

A media company stores video metadata in Amazon DynamoDB. The table has a partition key of videoId (string) and a sort key of uploadDate (number). The application frequently needs to retrieve all videos uploaded by a specific user (userId) within the last 30 days. Queries currently scan the entire table, causing high latency and cost. Which design change should a database specialist implement to optimize these queries?

Accepted Answer

Create a global secondary index with partition key userId and sort key uploadDate.. The application queries videos by userId and uploadDate range. A global secondary index with userId as partition key and uploadDate as sort key enables efficient, low-latency queries. This avoids full table scans, reduces cost, and scales with the workload. Other options either do not match the access pattern or introduce unnecessary complexity.

Answer

Enable DynamoDB Streams to capture changes and replicate data to Amazon S3 for querying with Amazon Athena.

Answer

Add a local secondary index with partition key videoId and sort key uploadDate.

Answer

Increase the read capacity units (RCUs) of the table to handle the scan operations more efficiently.