DBS-C01 Mock Exam 77 — 25 Questions

Question 1

A database administrator is troubleshooting a backup failure for an Amazon RDS for SQL Server DB instance. The error message states 'Insufficient storage capacity for backup. Free storage space is 0 GB.' The DB instance has 200 GB allocated storage. What is the most likely cause?

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

Accepted Answer

The DB instance has insufficient free storage space to perform the backup.. RDS requires free storage space to perform backups and manage transaction logs. With 0 GB free, the backup fails. Option B is incorrect because the number of manual snapshots does not affect the storage capacity of the DB instance; manual snapshots are stored separately in Amazon S3. Option C is incorrect because although transaction logs consume allocated storage, the error specifically indicates insufficient free storage for the backup operation, and the most likely cause is that the instance lacks free storage. Option D is incorrect because setting the backup retention period to 0 days disables automated backups entirely; it does not cause a backup failure due to insufficient storage.

Answer

The DB instance has reached the maximum number of manual snapshots.

Answer

The transaction logs are consuming all allocated storage.

Answer

The backup retention period is set to 0 days, disabling automated backups.

Question 2

A company runs an Amazon Aurora MySQL database with read replicas to handle read traffic. During a recent load test, the primary instance CPU utilization reached 90%, but read replicas remained below 50%. The application uses a custom ORM that connects to a single endpoint. Which change will best distribute read traffic?

Accepted Answer

Configure the application to use the Aurora reader endpoint for read queries.. The Aurora reader endpoint automatically load balances SELECT queries across all read replicas, distributing read traffic effectively. Option B is incorrect: Amazon RDS Proxy provides connection pooling but does not split read/write traffic; it uses the cluster endpoint, which directs to the primary instance. Option C is incorrect: Aurora read replicas are not standard EC2 instances and cannot be placed behind an Application Load Balancer; the reader endpoint is the intended mechanism. Option D is incorrect: The cluster endpoint always points to the primary instance, so using it for reads would not distribute load; Aurora Auto Scaling adds replicas, but they are only utilized when the reader endpoint is used.

Answer

Use Amazon RDS Proxy with read/write splitting.

Answer

Place the read replicas behind an Application Load Balancer.

Answer

Enable Aurora Auto Scaling for replicas and use the cluster endpoint for both read and write.

Question 3

A company is using Amazon DynamoDB for a web application. The company notices that read requests to a particular table are throttled during peak hours. The table has a provisioned read capacity of 1000 read capacity units (RCUs). The read requests are mostly eventually consistent reads. What should the company do to reduce throttling without changing the application code?

Accepted Answer

Increase the provisioned read capacity for the table.. Increasing provisioned read capacity directly provides more RCUs, reducing throttling without code changes. Option A is wrong because ElastiCache would require application code changes to implement caching. Option B is wrong: Switching to strongly consistent reads would double RCU consumption per read (for reads up to 4 KB) or increase it, worsening throttling. Option C is wrong: DAX does require code changes to integrate (though minimal), and the question specifically asks for no application code changes.

Answer

Use Amazon ElastiCache to cache the read results.

Answer

Switch to strongly consistent reads to reduce the number of read requests.

Answer

Implement DynamoDB Accelerator (DAX) to cache read requests.

Question 4

A company runs a critical application on Amazon RDS for MySQL with Multi-AZ deployment. The application performs frequent writes. The DB instance's CPU utilization is consistently above 80%, and the write latency is high. The company wants to improve write performance without changing the application code. Which solution is MOST effective?

Accepted Answer

Migrate the database to Amazon Aurora MySQL.. Migrating to Amazon Aurora MySQL is the most effective solution because Aurora uses a distributed, SSD-backed storage system with a separate log writer process that reduces write latency. Increasing the DB instance class (Option C) can improve CPU capacity but does not address the underlying storage write latency as effectively as Aurora. Adding a read replica (Option B) offloads read traffic but does not improve write performance. Enabling Multi-AZ with synchronous replication (Option A) is already in place and can increase write latency due to synchronous replication; it does not solve the high CPU utilization issue.

Answer

Enable Multi-AZ with synchronous replication to a standby instance.

Answer

Add a read replica to offload read traffic.

Answer

Increase the DB instance class to a larger size with more vCPUs.

Question 5

A gaming company uses Amazon DynamoDB for player profiles. The access pattern is to retrieve a player's profile by 'player_id'. Each profile includes a list of 'achievements' that can grow up to 400 KB. Recently, the application has been encountering 'ProvisionedThroughputExceededException' errors. The table has 1000 read capacity units (RCU) and 500 write capacity units (WCU). The average item size is 200 KB. What is the MOST likely cause of the throttling?

Accepted Answer

The application is using strongly consistent reads, which consume double the read capacity.. Strongly consistent reads in DynamoDB consume twice the read capacity units (RCUs) as eventually consistent reads. With an average item size of 200 KB, each strongly consistent read consumes 200 KB / 4 KB = 50 RCUs (rounded up). If the application is using strongly consistent reads, a single read of a 200 KB item uses 50 RCUs, which can quickly exhaust the 1000 RCU table capacity, especially under concurrent access, leading to ProvisionedThroughputExceededException.

Answer

The item size exceeds the DynamoDB item size limit of 400 KB.

Answer

The read capacity units are set too low for the number of partitions.

Answer

The partition key 'player_id' is causing hot partitions.

Question 6

A financial services company runs a critical application on Amazon RDS for PostgreSQL. They must ensure that database activity logs are sent to Amazon CloudWatch Logs for real-time monitoring. The logs must include all SQL queries, including SELECT statements. Which configuration will meet these requirements?

Accepted Answer

Set log_statement = 'all' and log_min_duration_statement = 0 in the DB parameter group. Enable CloudWatch Logs export.. Setting `log_statement = 'all'` captures every SQL statement, including SELECT, and `log_min_duration_statement = 0` ensures all statements are logged regardless of duration. Enabling CloudWatch Logs export then sends these logs to CloudWatch Logs for real-time monitoring. Option B is incorrect because while pgAudit can log all statements, it is not necessary; the built-in PostgreSQL logging with `log_statement = 'all'` meets the requirement without additional extensions. Option C is incorrect because `log_statement = 'ddl'` only logs data definition language statements, not SELECT queries. Option D is incorrect because `log_min_duration_statement = -1` disables logging of all statements.

Answer

Install the pgAudit extension and configure it to log all statements. Enable CloudWatch Logs export in the RDS console.

Answer

Set the parameter log_statement = 'ddl' in the DB parameter group. Enable CloudWatch Logs export.

Answer

Set log_min_duration_statement = -1 in the DB parameter group. Enable CloudWatch Logs export.

Question 7

A company is migrating an on-premises MongoDB database to Amazon DocumentDB (with MongoDB compatibility). The security team requires that data be encrypted at rest and in transit. Additionally, the team wants to use IAM roles to authenticate applications. Which THREE steps should the database specialist take to meet these requirements?

Accepted Answer

Use IAM roles to authenticate applications to the DocumentDB cluster.. Options A, C, and E are correct. IAM roles (A) can be used for authentication to DocumentDB, enabling fine-grained access control. Encryption at rest (C) can be enabled when creating the cluster, as DocumentDB supports encrypted storage using AWS KMS. Encryption in transit (E) is achieved by using TLS for all connections. Option B is incorrect because DocumentDB uses a trusted certificate authority for TLS, not a custom CA. Option D is incorrect because VPC endpoints provide private connectivity but do not enforce encryption; encryption is handled at the cluster level and via TLS.

Answer

Use a custom certificate authority for SSL/TLS.

Answer

Create a VPC endpoint for DocumentDB to enforce encryption.

Question 8

A developer is designing a DynamoDB table for an order management system using the above CloudFormation template. The application needs to query orders by CustomerID. The current design has a GSI on CustomerID. However, the developer notices that the GSI has low write throughput and often throttles. What is the most cost-effective way to improve write throughput on the GSI?

Accepted Answer

Increase the WriteCapacityUnits of the GSI from 5 to a higher value.. The GSI's write throughput is independent of the base table's write capacity. Increasing the GSI's WriteCapacityUnits directly addresses the throttling on the GSI without affecting the base table's cost or performance. This is the most cost-effective approach because it only scales the specific resource that is throttling, rather than over-provisioning the entire table or adding unnecessary infrastructure.

Answer

Change the ProjectionType of the GSI to KEYS_ONLY.

Answer

Use Amazon SQS to buffer writes to the table.

Answer

Increase the WriteCapacityUnits of the table.

Question 9

Which THREE factors should be considered when choosing between Amazon RDS and Amazon DynamoDB for a new application? (Choose THREE.)

Accepted Answer

The query patterns and access methods required by the application.. The choice between Amazon RDS (relational) and DynamoDB (NoSQL) hinges on the application's data access patterns. RDS supports complex SQL queries with joins, aggregations, and secondary indexes, while DynamoDB is optimized for key-value and document queries with predictable, low-latency access patterns. If the application requires flexible querying with ad-hoc filters, RDS is appropriate; if it needs high-throughput, single-key lookups or simple query patterns, DynamoDB is better suited.

Answer

The requirement for encryption at rest.

Answer

The need for multi-AZ high availability.

Question 10

A financial services company uses Amazon DynamoDB to store sensitive customer data. The security team requires that all data at rest be encrypted using a customer-managed AWS KMS key (CMK) with automatic rotation enabled. The DynamoDB table was created with the default AWS-managed key. Which steps are necessary to transition to a customer-managed CMK while minimizing downtime and data loss?

Accepted Answer

Export the table data to Amazon S3, create a new DynamoDB table with the new CMK, import the data, and update the application to use the new table.. DynamoDB does not support in-place modification of the encryption key for an existing table. To transition from an AWS-managed key to a customer-managed CMK, you must export the table data to Amazon S3, create a new DynamoDB table configured with the new CMK, import the data, and update the application to point to the new table. This approach minimizes downtime by allowing the original table to serve reads/writes during the export and import process, and avoids data loss by using DynamoDB's native export and import features.

Answer

Modify the DynamoDB table to update the encryption key to the new CMK using the AWS Console.

Answer

Disable encryption at rest, then re-enable it with the new CMK.

Answer

Update the KMS key policy to grant DynamoDB access to the new CMK, then rotate the key.

Question 11

A company is moving a self-hosted MySQL database to Amazon Aurora MySQL. The current database uses InnoDB with full-text indexes and triggers. The migration must be done with zero downtime. Which approach meets these requirements?

Accepted Answer

Use AWS DMS with ongoing replication from the source MySQL database. AWS DMS with ongoing replication (change data capture) allows continuous synchronization from the source MySQL database to Amazon Aurora MySQL, enabling a zero-downtime migration. DMS captures incremental changes from the source's binary logs (binlog) and applies them to the target, so the database remains fully operational during the migration. This approach also supports InnoDB tables, full-text indexes, and triggers, as DMS handles schema and data replication for these features. Option C (native MySQL binlog replication) is supported by Aurora MySQL, but it requires an initial seed of data which introduces downtime because the source database typically needs to be in a read-only state for a consistent backup. In contrast, DMS with CDC avoids any initial downtime.

Answer

Use mysqldump to export the database and import into Aurora

Answer

Set up MySQL replication from on-premises to Aurora using native binlog replication

Answer

Export data to Amazon S3 and use Aurora's LOAD DATA FROM S3 command

Question 12

A company has an Amazon Aurora MySQL DB cluster with a single writer and two readers. The writer instance fails, and the failover mechanism promotes one of the readers to writer. The application, which uses a custom connection pool, continues to experience errors for several minutes. What should the database administrator do to minimize downtime during future failovers?

Accepted Answer

Modify the application to use the cluster endpoint instead of the instance endpoint.. The cluster endpoint always points to the current writer, so after a failover it automatically routes to the new writer without application changes. Option A is wrong because increasing the connection pool size does not help the application detect the new writer; it could even cause more failed connections. Option C is wrong because the reader endpoint only routes to read replicas, not the writer, so write traffic would fail. Option D is wrong because Aurora already provides Multi-AZ replication; there is no separate 'enable Multi-AZ' setting.

Answer

Increase the connection pool size to handle more connections.

Answer

Configure the application to use the reader endpoint for all traffic.

Answer

Enable Multi-AZ on the Aurora cluster.

Question 13

A company runs an Amazon RDS for MySQL Multi-AZ DB instance. The application experiences intermittent read latency spikes. The DB instance type is db.r5.large with 500 GB of General Purpose SSD (gp2) storage. The spike occurs during peak hours when read activity is high. Which action would most effectively reduce read latency?

Accepted Answer

Create an Amazon RDS read replica and direct read traffic to it.. Adding an RDS read replica offloads read traffic from the primary DB instance, reducing read contention and latency. Option A is incorrect because changing to io1 improves I/O performance but does not address read contention from high read load on the primary. Option B is incorrect because Multi-AZ provides high availability but the standby replica does not serve read traffic. Option C is incorrect because increasing storage increases baseline IOPS but does not offload read operations.

Answer

Change the storage type to Provisioned IOPS (io1).

Answer

Enable Multi-AZ with a standby replica.

Answer

Increase the allocated storage to 1 TB to improve IOPS.

Question 14

A company is running a production Amazon RDS for MySQL DB instance. The application team reports intermittent high latency and connection timeouts. A quick check shows that the DB instance's CPU utilization is consistently above 90% during peak hours. The database size is 500 GB and the instance class is db.r5.large. Which combination of actions should a database specialist take to resolve the performance issue?

Accepted Answer

Scale up the DB instance to db.r5.xlarge and review slow query logs to optimize poorly performing queries.. Scaling up the DB instance to db.r5.xlarge provides more compute capacity, directly addressing high CPU utilization. Additionally, reviewing slow query logs helps identify and optimize inefficient queries that may be causing CPU spikes. Option A is incorrect because increasing storage does not improve CPU performance; it only addresses storage capacity or I/O issues. Option C is incorrect because enabling Multi-AZ provides high availability but does not increase compute capacity, and increasing storage does not help with CPU. Option D is incorrect because Performance Insights helps diagnose performance issues but does not resolve them, and CloudWatch alarms only provide notifications without fixing the underlying problem.

Answer

Increase the allocated storage to 1 TB and enable auto-scaling for storage.

Answer

Enable Multi-AZ and increase the allocated storage to 1 TB to improve I/O performance.

Answer

Enable Performance Insights and create a CloudWatch alarm to notify when CPU exceeds 80%.

Question 15

A team is troubleshooting an Amazon RDS for SQL Server instance that is running out of storage. The instance uses General Purpose SSD (gp2) storage. The team wants to increase storage without downtime. Which action should they take?

Accepted Answer

Modify the DB instance to increase allocated storage.. Amazon RDS allows you to modify the allocated storage for a DB instance dynamically without downtime; the change takes effect during the next maintenance window or can be applied immediately. Option A is incorrect because migrating from gp2 to gp3 changes the storage type but does not increase the storage capacity. Option B is incorrect because adding a read replica does not increase storage on the primary instance; it only offloads read traffic. Option C is incorrect because while you can restore a snapshot to a larger instance, this process involves downtime and is not as straightforward as modifying the storage directly.

Answer

Migrate to gp3 storage.

Answer

Add a read replica to offload queries.

Answer

Take a snapshot and restore to a larger instance.

Question 16

A financial services company uses Amazon DynamoDB to store transaction records. Each transaction has a partition key of customer_id and a sort key of transaction_timestamp. The application queries transactions for a specific customer within a date range. Recently, the query latency increased significantly for customers with a large number of transactions. The company needs to improve query performance without changing the application code. The table is provisioned with 5000 RCUs and 2000 WCUs. Which design change should be made to optimize for this workload?

Accepted Answer

Create a global secondary index with customer_id as partition key and transaction_timestamp as sort key.. Creating a global secondary index (GSI) with customer_id as the partition key and transaction_timestamp as the sort key allows efficient querying of transactions for a specific customer within a date range. The existing table's sort key is transaction_timestamp, but the GSI provides a separate index optimized for this access pattern, avoiding full table scans on large customer partitions. This improves query performance without requiring application code changes, as the application can query the GSI directly.

Answer

Enable DynamoDB Accelerator (DAX) on the table.

Answer

Increase the provisioned RCUs to 10000.

Answer

Change the sort key to a composite key including a tenant identifier.

Question 17

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The security team requires that all connections to the database use Oracle Native Network Encryption (NNE). How should this be configured?

Accepted Answer

Create a custom DB parameter group with the encryption parameters set to REQUIRED.. RDS for Oracle supports Oracle Native Network Encryption (NNE) through custom DB parameter groups. You must set the SQLNET.ENCRYPTION_SERVER parameter to REQUIRED and optionally specify encryption types. Option A (IAM database authentication) does not encrypt the network connection. Option B is incorrect because RDS does not allow direct editing of sqlnet.ora files; parameter groups are the correct method. Option D (encryption at rest) protects stored data, not data in transit.

Answer

Enable IAM database authentication.

Answer

Modify the sqlnet.ora file on the RDS instance to require encryption.

Answer

Enable encryption at rest using Oracle TDE.

Question 18

A database administrator notices that an Amazon RDS for MySQL DB instance has experienced a failover during a maintenance window. What is the most likely cause of this failover?

Accepted Answer

A system update was applied during the maintenance window, causing a reboot. The RDS maintenance window is used to apply system updates, which may require a reboot and failover if Multi-AZ is enabled. Option A is wrong because running out of storage does not cause a failover; instead, it would cause the instance to become unavailable. Option B is wrong because promoting a read replica is a manual action, not an automatic failover during maintenance. Option C is wrong because a manual failover is initiated by the administrator, not automatically during the maintenance window.

Answer

The DB instance ran out of storage and automatically failed over

Answer

A read replica was promoted to a primary instance

Answer

A manual failover was initiated by the administrator

Question 19

An organization wants to migrate a 200 GB MySQL database from an on-premises server to Amazon Aurora MySQL. They have a 50 Mbps network connection. The database is 8 hours of downtime. The migration must be completed within 24 hours and costs must be minimized. The team decides to use AWS Database Migration Service (DMS). Which approach best meets the requirements?

Accepted Answer

Use AWS DMS with a full load and ongoing replication to minimize downtime.. Using a DMS full load with ongoing replication minimizes downtime and works within the network constraints. Option A is wrong because taking a dump over the network would take too long. Option C is wrong because using Snowball is overkill for 200 GB and shipping would take too long. Option D is wrong because using a larger instance is unnecessary and costly.

Answer

Create a mysqldump and transfer it over the network to S3, then restore to Aurora.

Answer

Use AWS Snowball Edge to transfer the data physically.

Answer

Provision a large EC2 instance to run a parallel export and import.

Question 20

A company is migrating a 1 TB SQL Server database to Amazon RDS for SQL Server. The migration window is 4 hours. The on-premises network bandwidth is 1 Gbps. The database is not actively used during the migration window. The team wants to minimize migration time and cost. Which migration strategy is most appropriate?

Accepted Answer

Use AWS DMS with full load only.. AWS DMS with full load only (Option D) is the most appropriate strategy for this migration. With a 1 Gbps network, the theoretical transfer time for 1 TB is about 2.2 hours (1 TB = 8000 Gb, 8000 Gb / 1 Gbps = 8000 seconds ≈ 2.22 hours), well within the 4-hour window. AWS DMS performs a direct, efficient full-load migration without requiring intermediate storage or additional tools. Option A (BCP + DTS) is slower and more complex. Option B (Snowball) adds cost and logistics that are unnecessary given the network speed. Option C (native backup to S3 and restore) requires uploading the backup to S3 first, then restoring to RDS, which is typically slower than DMS's direct streaming approach.

Answer

Use SQL Server BCP utility to export data and then import using DTS.

Answer

Use AWS Snowball to transfer the database files.

Answer

Create a native backup, upload to S3, restore to RDS.