DBS-C01 Mock Exam 89 — 25 Questions

Question 1

A company runs an Amazon Aurora MySQL DB cluster with one writer and two readers. The application experiences increased read latency. The DBA wants to offload read traffic from the writer instance. Which configuration change should be made to the application?

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

Accepted Answer

Modify the application to use the reader endpoint for read queries.. The reader endpoint for an Aurora MySQL cluster automatically load-balances read-only connections across all available reader instances. By modifying the application to use the reader endpoint for read queries, read traffic is offloaded from the writer instance, reducing read latency on the writer. This is the standard AWS-recommended pattern for separating read and write workloads in Aurora.

Answer

Modify the application to use an individual instance endpoint for each reader.

Answer

Create a custom endpoint that includes both writer and readers.

Answer

Modify the application to use the cluster endpoint for all queries.

Question 2

A retail company uses Amazon DynamoDB to store product catalog data. The security team wants to ensure that only authorized applications can read and write to the table. The applications are running on Amazon EC2 instances. The current setup uses an IAM role attached to the EC2 instance with a policy that grants dynamodb:* on the specific table. However, during a security audit, it was discovered that any process on the EC2 instance can access the table because the instance has access to the temporary credentials from the instance metadata service. The security team requires that only specific processes (the application) can access the credentials, and that the credentials cannot be extracted from the instance. What should be done to meet these requirements?

Accepted Answer

Create a VPC endpoint for DynamoDB with a policy that restricts access to the specific IAM role, and configure the EC2 instance to use IMDSv2 with a hop limit.. Using a VPC endpoint for DynamoDB with a policy that restricts access to the specific IAM role ensures that only requests from that role are allowed, and using IMDSv2 with a hop limit prevents credential theft by ensuring that only the intended application process on the EC2 instance can access the credentials. Option B is incorrect because security groups control network traffic but do not enforce IAM role usage. Option C is incorrect because storing AWS access keys on the instance is less secure and exposes credentials to any process. Option D is incorrect because DynamoDB does not support resource-based policies; IAM roles are authorized via identity-based policies attached to the role.

Answer

Modify the security group to only allow traffic from the EC2 instance's private IP.

Answer

Store AWS access keys on the EC2 instance and use them in the application.

Answer

Attach a resource-based policy to the DynamoDB table allowing only the EC2 instance's IAM role.

Question 3

A company runs a critical e-commerce application on Amazon RDS for MySQL with Multi-AZ enabled. The database is 2 TB and uses General Purpose (gp2) storage. Recently, during peak hours, the application experienced a 5-minute outage. The CloudWatch logs show that the primary DB instance failed and an automatic failover occurred. However, the failover took 3 minutes, which is longer than the expected 1-2 minutes. The 'ReadLatency' and 'WriteLatency' metrics were elevated before the failure. The 'BurstBalance' metric was at 0% for the hour before the failure. The team suspects the issue is related to storage performance. What should the team do to prevent this issue in the future?

Accepted Answer

Change the storage type to Provisioned IOPS (io1).. The BurstBalance at 0% indicates the gp2 volume exhausted its burst credits, causing I/O throttling and increased latency, which likely contributed to the failover delay. Switching to Provisioned IOPS (io1) provides consistent performance and avoids burst credit exhaustion. Option A is wrong because increasing the DB instance class addresses compute capacity, not storage I/O. Option C is wrong because backup retention period does not affect storage performance. Option D is wrong because read replicas offload read traffic but do not improve write performance on the primary instance.

Answer

Increase the DB instance class to a larger size.

Answer

Increase the backup retention period to 35 days.

Answer

Create a read replica to offload read traffic.

Question 4

A database administrator is monitoring an Amazon RDS for SQL Server DB instance and notices that the FreeableMemory metric is consistently below 200 MB. Which of the following actions is most appropriate to mitigate performance issues?

Accepted Answer

Scale up the DB instance to a larger instance class with more memory. A low FreeableMemory metric consistently below 200 MB indicates memory pressure on the RDS for SQL Server DB instance. The most effective mitigation is to scale up to a larger instance class with more memory, directly addressing the resource shortage. Option D is correct because it increases available memory. Option B is incorrect because disabling SQL Server Agent and error logging does not free significant memory and may disrupt essential operations. Option A is incorrect because changing the maintenance window does not affect memory usage. Option C is incorrect because enabling backups with a shorter retention period does not impact memory.

Answer

Modify the DB instance's maintenance window to off-peak hours

Answer

Disable the SQL Server Agent and error logging

Answer

Enable automatic backups with a shorter retention period

Question 5

A company is running a MongoDB-compatible Amazon DocumentDB cluster. The application is experiencing high write latency during peak hours. The cluster has one writer and two readers. The DBA suspects that the issue is due to a large number of indexes on the collection. What should the DBA do to verify this hypothesis without affecting production?

Accepted Answer

Create a clone of the cluster using the 'Clone Cluster' feature and test index changes on the clone.. Cloning the cluster using the 'Clone Cluster' feature creates a separate, isolated environment where index changes can be tested without affecting production. Option A is incorrect because taking a snapshot and restoring to a new cluster is time-consuming and does not provide a real-time copy of the current state for testing. Option B is incorrect because AWS DMS is designed for database migration, not for testing index performance. Option C is incorrect because enabling the profiler captures slow queries but does not allow testing of index changes; it only helps identify existing issues.

Answer

Take a snapshot of the cluster and restore it to a new cluster to test index changes.

Answer

Use AWS DMS to replicate data to a test cluster and perform index testing there.

Answer

Enable the profiler on the production cluster to capture slow queries and analyze the index usage.

Question 6

A company is migrating a PostgreSQL database to Amazon Aurora PostgreSQL. They want to use the AWS DMS for the migration. Which THREE resources need to be created in the AWS account?

Accepted Answer

DMS target endpoint pointing to Aurora PostgreSQL.. AWS DMS requires a target endpoint that specifies the connection details for the Amazon Aurora PostgreSQL database. This endpoint tells DMS where to load the migrated data, and it must be configured with the correct database name, credentials, and VPC settings to ensure successful connectivity during the migration task.

Answer

Application Load Balancer for the replication instance.

Answer

AWS CloudFormation stack to provision resources.

Question 7

A company runs a production Amazon RDS for PostgreSQL database with automated backups enabled. A database administrator accidentally dropped a critical table. The administrator wants to restore the table from a point in time before the drop. The database is 1 TB in size and the recovery point objective (RPO) is 5 minutes. Which approach minimizes downtime?

Accepted Answer

Use the point-in-time recovery feature to restore the database to a new DB instance at a time before the drop, then use pg_dump to export the table and import it into the production database.. Amazon RDS Point-in-Time Recovery (PITR) allows restoring to any second within the backup retention window, enabling a restore to just before the table was dropped. After restoring to a new DB instance, pg_dump can export the specific table, and then pg_restore or psql can import it into the production database. This minimizes downtime by avoiding a full database restore and only moving the single dropped table.

Answer

Restore the automated backup from S3 to a new EC2 instance running PostgreSQL, then export the table and import it into the production database.

Answer

Restore the database from the most recent manual snapshot to a new instance, then use pg_dump to extract the table and import it into the production database.

Answer

Create a read replica from the production database, stop replication, and use pg_dump to extract the table from the replica and import it into the production database.

Question 8

A company is migrating an on-premises MongoDB database to Amazon DocumentDB (with MongoDB compatibility). They want to validate that the data is consistent after migration. Which tool should they use?

Accepted Answer

AWS DMS data validation. AWS DMS data validation is the correct tool because it provides built-in, row-level checksum-based validation that compares source and target data after a full load or ongoing replication. For DocumentDB migrations, DMS can compute and compare checksums on the fly, ensuring consistency without requiring manual scripting or external tools. This is the recommended AWS approach for validating data integrity during and after a migration to DocumentDB.

Answer

mongoexport and mongoimport

Answer

dbHash command on both databases

Answer

DocumentDB native consistency check tool

Question 9

A company is migrating a 1 TB on-premises SQL Server database to Amazon RDS for SQL Server. The migration must be completed within 24 hours and with minimal downtime. Which TWO approaches should be used? (Choose 2)

Accepted Answer

Use AWS DMS with ongoing replication (CDC).. AWS DMS with ongoing replication (CDC) allows you to perform a full load of the existing data and then continuously replicate changes from the source SQL Server database to Amazon RDS for SQL Server, minimizing downtime to just the final cutover window. This approach meets the 24-hour migration window and the requirement for minimal downtime by keeping the target database nearly synchronized with the source until you are ready to switch.

Answer

Use AWS DMS with SSIS packages.

Answer

Use native backup and restore to S3.

Answer

Use AWS DMS full load only.

Question 10

A company is using Amazon RDS for SQL Server with native backup and restore. The backup process is failing with an error indicating insufficient disk space for the backup file. The DB instance has 200 GB of allocated storage, and the backup file is 50 GB. What should the database administrator do to resolve this issue?

Accepted Answer

Increase the allocated storage for the RDS instance. Native backups in RDS for SQL Server are stored in the instance's attached storage. When the allocated storage is full, the backup fails due to insufficient disk space. Increasing the allocated storage provides additional space for the backup file. Option A is incorrect because changing to Provisioned IOPS affects performance, not storage capacity. Option C is incorrect because the error is about disk space, not permissions. Option D is incorrect because switching to automated backups would not resolve the immediate failure of the native backup process, and the question specifically addresses native backup failure.

Answer

Change the storage type to Provisioned IOPS for better performance

Answer

Grant the rds_backup user additional permissions to write to S3

Answer

Switch to automated backups instead of native backups

Question 11

A gaming company uses Amazon DynamoDB as the primary data store for player profiles and game state. The application experiences sudden spikes in traffic during new game launches, causing throttling on write requests. The current table has on-demand capacity mode. The table's partition key is 'player_id' (high cardinality). The read/write patterns are evenly distributed. Despite on-demand mode, throttling occurs because the per-partition throughput limit is being reached. The company wants to eliminate throttling without changing the partition key. Which solution should be recommended?

Accepted Answer

Enable DynamoDB adaptive capacity and implement write sharding using a random suffix.. On-demand capacity mode already scales automatically, but per-partition throughput limits can still be reached if a single partition receives too many writes. Adaptive capacity (enabled by default) helps by dynamically adjusting per-partition throughput based on traffic patterns. However, if a specific partition key value experiences hot-spotting, write sharding—adding a random suffix to the partition key—further distributes writes across multiple partitions, increasing overall write capacity. Option A (DAX) caches reads, not writes. Option B (auto scaling with provisioned) does not solve per-partition limits; it adjusts table-level capacity. Option D (provisioned with increased WCU) also addresses table-level capacity, not per-partition limits.

Answer

Implement Amazon DynamoDB Accelerator (DAX) to offload read traffic.

Answer

Use DynamoDB auto scaling with provisioned capacity.

Answer

Switch to provisioned capacity mode and increase write capacity units.

Question 12

A company is migrating a 500 GB Oracle database to Amazon RDS for Oracle. The migration must complete within a 4-hour downtime window. The network bandwidth is 1 Gbps. Which migration approach minimizes the migration time?

Accepted Answer

Use AWS DMS to perform a full load of the database to RDS.. AWS DMS performs a full load directly from the source Oracle database to the target RDS for Oracle instance over the network, leveraging the 1 Gbps bandwidth efficiently. For a 500 GB database, a full load at 1 Gbps (theoretical max ~450 Gbps per hour) can complete in under 2 hours, well within the 4-hour window, without requiring intermediate storage or schema conversion.

Answer

Use AWS Schema Conversion Tool (SCT) to convert the schema, then use AWS DMS for data migration.

Answer

Use Oracle Data Pump to export and import the database.

Answer

Use AWS DataSync to copy the database files to Amazon S3, then restore to RDS.

Question 13

A company is migrating a 1 TB Oracle database to Amazon RDS for Oracle. The source database has a high volume of small transactions. The migration must minimize source database impact. Which AWS DMS configuration should be used?

Accepted Answer

Use full load only and disable ongoing replication. Using full load only with ongoing replication disabled minimizes source database impact by avoiding the overhead of capturing and applying continuous change data capture (CDC) logs. The high volume of small transactions would otherwise generate a large number of redo log switches and increase I/O on the source, which is contrary to the requirement to minimize impact. A full load only migration transfers a snapshot of the data once, reducing the source load to a single consistent read operation.

Answer

Use batch-optimized apply mode

Answer

Use full load with CDC (ongoing replication)

Answer

Use multiple DMS tasks to parallelize the migration

Question 14

A database administrator notices that an Amazon RDS for MySQL DB instance is experiencing high CPU utilization and increased latency during peak hours. The administrator wants to identify the queries causing the issue. Which TWO actions should be taken to diagnose the problem? (Select TWO.)

Accepted Answer

Enable Performance Insights on the DB instance.. Enabling Performance Insights provides database performance metrics including wait events and SQL query details, allowing identification of queries causing high CPU and latency. Option C: Enabling the slow query log captures queries that exceed a specified duration threshold, helping to pinpoint slow-running queries. Option B (Amazon DevOps Guru for RDS) is an automated service for anomaly detection and performance insights, not a direct method to identify specific queries. Option D (RDS Proxy) manages connection pooling and improves scalability, but does not identify problematic queries. Option E (RDS Enhanced Monitoring) provides OS-level metrics, not query-level details.

Answer

Enable Amazon DevOps Guru for RDS.

Answer

Use RDS Proxy to manage connections.

Answer

Enable RDS Enhanced Monitoring.

Question 15

A database engineer is troubleshooting slow query performance on an Amazon RDS for PostgreSQL instance. The instance is db.r5.large with 500 GB of General Purpose SSD (gp2) storage. CloudWatch metrics show high Read Latency and high Read IOPS, but low CPU utilization. Which TWO actions should the engineer take to improve performance?

Accepted Answer

Create a read replica and offload read queries to it.. A is correct because creating a read replica offloads read queries from the primary instance, reducing the read IOPS and read latency on the primary. This directly addresses the high Read Latency and high Read IOPS metrics without requiring a larger instance class or storage change, especially since CPU utilization is low, indicating the bottleneck is I/O, not compute.

Answer

Increase the DB instance class to a larger size, such as db.r5.2xlarge.

Answer

Enable Multi-AZ to use the standby for read traffic.

Answer

Optimize queries by adding appropriate indexes.

Question 16

A company is running a production Amazon Aurora MySQL-Compatible Edition database. The database has recently experienced several failovers due to replica lag. The DBA needs to implement monitoring to detect replica lag early. Which THREE metrics should be monitored to assess replication health? (Select THREE.)

Accepted Answer

DatabaseConnections. (DatabaseConnections) can indirectly indicate replication issues if application retries increase due to failovers. Option C (ReplicaLag) is the standard MySQL metric measuring replication lag. Option E (AuroraReplicaLag) is the direct Aurora-specific metric for replica lag. The other options are not directly related to replication health: ActiveTransactions (B) measures transaction volume, not replication lag, and BufferCacheHitRatio (D) is about cache efficiency.

Answer

ActiveTransactions

Answer

BufferCacheHitRatio

Question 17

A gaming company uses Amazon DynamoDB with global tables across two regions. They notice increased write latency and throttling during peak hours. The access pattern is mostly writes to a small set of hot partitions. Which design change would best address this?

Accepted Answer

Implement write sharding using a random suffix on the partition key. The issue is hot partitions caused by a small set of partition keys receiving the majority of writes. By implementing write sharding with a random suffix on the partition key, you distribute writes across multiple partitions, reducing throttling and write latency. This directly addresses the root cause of uneven access patterns, unlike the other options that either cache reads, adjust capacity mode, or scale capacity without solving the partition-level bottleneck.

Answer

Enable DynamoDB Accelerator (DAX)

Answer

Switch to DynamoDB on-demand capacity mode

Answer

Increase write capacity using auto scaling

Question 18

A data engineer is troubleshooting a slow-running query on an Amazon Redshift cluster. The query involves large table joins and aggregations. Which diagnostic step should be taken FIRST to understand the query execution plan and identify bottlenecks?

Accepted Answer

Run the EXPLAIN command on the query to review the execution plan.. The EXPLAIN command is the first and most direct step to understand how Redshift plans to execute a query, including join types, data distribution, and aggregation strategies. It reveals the execution plan without running the query, allowing the engineer to identify bottlenecks like nested loop joins or missing sort key optimization before any other diagnostic step.

Answer

Monitor the WLM queue metrics for the query.

Answer

Check the SVV_TABLE_INFO view for table distribution and sort keys.

Answer

Query the STL_QUERY system table to review the query text.

Question 19

A company is using Amazon RDS for PostgreSQL and needs to implement column-level encryption for sensitive data. The application must be able to encrypt and decrypt data transparently. Which approach should be taken?

Accepted Answer

Install the pgcrypto extension on the RDS instance and use its functions to encrypt data at the column level.. Pgcrypto is a PostgreSQL extension that provides column-level encryption functions, allowing the application to encrypt and decrypt data transparently at the column level. Option A is incorrect because RDS encryption at rest encrypts the entire database storage, not individual columns. Option B is incorrect because using AWS Lambda would require application modifications and introduce additional latency. Option C is incorrect because AWS KMS is a key management service, not a direct column-level encryption solution for databases, and using its APIs would require building encryption logic in the application.

Answer

Enable RDS encryption at rest using a KMS key, which will automatically encrypt all columns.

Answer

Use AWS Lambda to encrypt data before writing to the database and decrypt after reading.

Answer

Use the AWS KMS Encrypt and Decrypt APIs directly in the application code.

Question 20

A developer needs to securely store database credentials for an application that runs on Amazon EC2 and connects to an Amazon RDS for PostgreSQL database. The credentials must be automatically rotated every 90 days. Which AWS service should the developer use to meet these requirements?

Accepted Answer

AWS Secrets Manager. AWS Secrets Manager. Secrets Manager is designed to securely store and manage secrets such as database credentials. It natively supports automatic rotation of credentials for Amazon RDS databases, including PostgreSQL, with a customizable rotation interval (e.g., every 90 days). Option A (AWS Systems Manager Parameter Store) can store secrets but does not provide built-in automatic rotation for RDS credentials. Option B (AWS CloudHSM) provides hardware security modules for encryption key storage, not for managing database credentials. Option C (IAM roles) allow EC2 instances to assume roles for API access but do not store or rotate database credentials; while IAM database authentication can be used with RDS PostgreSQL, it does not meet the requirement to store and rotate credentials automatically.

Answer

AWS Systems Manager Parameter Store

Answer

AWS CloudHSM

Answer

AWS Identity and Access Management (IAM) roles