DBS-C01 Mock Exam 72 — 25 Questions

Question 1

A company is migrating an on-premises MongoDB database to Amazon DocumentDB. The current MongoDB workload uses aggregation pipelines with the $lookup stage and geospatial queries. The migration tool reports that some aggregation stages are not supported. Which THREE actions should the company take to address the incompatibilities?

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

Accepted Answer

Use $geoNear for geospatial queries as it is supported in DocumentDB.. DocumentDB supports the $geoNear aggregation stage for geospatial queries, making option B a valid action to address incompatibilities. The migration tool flagged unsupported stages, and $geoNear is explicitly supported in DocumentDB for location-based queries, whereas $geoWithin is not available in aggregation pipelines.

Answer

Replace $lookup with $geoWithin for location-based queries.

Answer

Convert $graphLookup to use recursive queries in DocumentDB.

Question 2

A database administrator runs the above AWS CLI command to troubleshoot replication issues. The DB instance 'mydb' is a read replica of 'my-source-db'. The administrator notices that the replica lag is increasing. Which of the following is the MOST likely cause?

Accepted Answer

The read replica is in a different AWS Region than the source.. When a read replica is in a different AWS Region than the source, the replication traffic must traverse the public internet or a VPN connection, introducing network latency and potential bandwidth constraints. This cross-region lag is a common cause of increasing replica lag, as the asynchronous MySQL replication relies on a single I/O thread to download the binary log events from the source, and any network delay directly impacts the replica's ability to keep up.

Answer

The source DB instance is running a different MySQL version.

Answer

The read replica has Multi-AZ disabled.

Answer

The read replica is using a smaller instance class than the source.

Question 3

A company has an Amazon Aurora MySQL DB cluster with a primary instance and two Aurora Replicas. The application is experiencing high write latency. The primary instance's CPU utilization is at 90%, while the replicas are at 30%. The DB cluster parameter group has the default values. Which change is most likely to reduce write latency?

Accepted Answer

Disable the binary log (binlog) on the DB cluster.. High CPU utilization on the primary instance is often caused by the binary log (binlog) being enabled, which is enabled by default for Aurora MySQL. Binlog generation adds overhead to write operations. Disabling binlog reduces CPU usage on the primary, thereby reducing write latency. Increasing the instance class (Option A) could help but is not as directly targeted as disabling binlog. Adding more Aurora Replicas (Option B) does not reduce write latency on the primary because replicas handle read traffic only. Increasing allocated storage (Option D) does not affect CPU or write latency.

Answer

Increase the DB instance class of the primary instance.

Answer

Add more Aurora Replicas to distribute the write load.

Answer

Increase the allocated storage of the cluster.

Question 4

A company is using Amazon DynamoDB with global tables. The application is experiencing high write latency in one region. Which THREE factors could contribute to this issue? (Choose three.)

Accepted Answer

Replication lag from global tables causing write conflicts.. Replication lag in global tables can lead to write conflicts and increased latency. Option C is correct because high network latency between the application and the DynamoDB endpoint directly impacts write latency. Option E is correct because insufficient write capacity units provisioned can cause throttling, resulting in higher write latency. Option B is incorrect because read capacity units do not affect write throughput. Option D is incorrect because aggressive auto scaling increases capacity, which would reduce latency, not increase it.

Answer

Insufficient read capacity units provisioned for the table.

Answer

The table's auto scaling configuration is set to increase write capacity too aggressively.

Question 5

Which THREE steps should be taken to troubleshoot an Amazon DynamoDB table that is experiencing high read latency?

Accepted Answer

Review the table's partition distribution using DynamoDB metrics.. High read latency in DynamoDB can result from uneven partition distribution, where a 'hot' partition receives more read requests than others, causing throttling or increased latency. By reviewing the table's partition distribution using CloudWatch metrics like `ConsumedReadCapacityUnits` per partition, you can identify skewed access patterns and address them with strategies like partition key redesign or adaptive capacity.

Answer

Increase the write capacity of the table.

Answer

Disable auto scaling to prevent unexpected capacity changes.

Question 6

A company is migrating a 5 TB Microsoft SQL Server database to Amazon RDS for SQL Server. The database has many stored procedures and triggers. The migration must have minimal downtime. Which approach should be used?

Accepted Answer

Use AWS DMS with full load and ongoing replication (CDC).. AWS DMS with full load and ongoing change data capture (CDC) enables continuous replication of changes from the source SQL Server to the target Amazon RDS for SQL Server, minimizing downtime to a brief cutover window. This approach handles the migration of stored procedures and triggers as part of the schema conversion via AWS SCT, while CDC captures ongoing transactions to keep the target synchronized until the final switch.

Answer

Use AWS SCT to convert the database schema and then use DMS for data load.

Answer

Use the SQL Server Import/Export wizard to copy data.

Answer

Take a native backup, copy to Amazon S3, and restore to RDS during a maintenance window.

Question 7

A database specialist is trying to connect to an Amazon RDS for MySQL instance from an EC2 instance but receives a 'Connection timed out' error. The security group for the RDS instance allows inbound traffic on port 3306 from the security group of the EC2 instance. What should the specialist check next?

Accepted Answer

Check the network ACL associated with the subnet of the RDS instance to ensure it allows inbound traffic on port 3306 and outbound traffic on ephemeral ports.. The 'Connection timed out' error suggests the packet is being dropped at the network layer, likely by a network ACL. Since the security group allows inbound on port 3306, the next step is to check the network ACL associated with the RDS instance's subnet. Network ACLs are stateless, so they must allow both inbound traffic on port 3306 and outbound traffic on ephemeral ports for the response. Option B is incorrect because a timed out error occurs before the TCP handshake completes, so DNS resolution is not the issue. Option C is incorrect because an internet gateway and public route are irrelevant if both instances are in the same VPC or connected privately. Option D is incorrect because the security group for the EC2 instance can be stateful and typically allows outbound traffic by default; the timeout is not caused by missing outbound rules on the EC2 side.

Answer

Check that the RDS instance has a public DNS name and the EC2 instance can resolve it.

Answer

Ensure that the VPC has an internet gateway attached and the route table has a route to it.

Answer

Verify that the security group for the EC2 instance allows outbound traffic on port 3306.

Question 8

A company is using Amazon Aurora MySQL-Compatible Edition. The database is experiencing performance degradation due to long-running queries. The DBA needs to identify the queries that are consuming the most resources. Which action should be taken?

Accepted Answer

Use Amazon RDS Performance Insights to identify the top SQL queries.. Amazon RDS Performance Insights is the correct tool for this scenario because it provides a built-in, easy-to-use dashboard that visualizes database load and identifies the top SQL queries consuming the most resources, such as CPU, I/O, and wait events. Unlike other options, Performance Insights directly correlates database performance metrics with specific queries, enabling the DBA to quickly pinpoint long-running or resource-intensive queries without additional setup or third-party tools.

Answer

Enable Enhanced Monitoring and review the OS process list.

Answer

Enable the slow query log and use a third-party tool to analyze it.

Answer

Enable CloudWatch Logs for the DB instance and search for errors.

Question 9

Refer to the exhibit. A company is migrating from an on-premises MySQL database to Amazon RDS for MySQL. The DBA wants to connect to the RDS instance using the endpoint shown. What additional step is required to allow the DBA's client to connect?

Accepted Answer

Modify the security group to allow inbound traffic on port 3306 from the client IP. Amazon RDS security groups act as a virtual firewall controlling inbound and outbound traffic. By default, no inbound traffic is allowed on port 3306 (MySQL). To permit the DBA's client to connect, you must modify the security group associated with the RDS instance to add an inbound rule that allows TCP traffic on port 3306 from the client's IP address (or a range that includes it). Without this rule, the connection is blocked at the network level regardless of other configurations.

Answer

Create a Route 53 record for the endpoint

Answer

Create a MySQL user that matches the client's IP

Answer

Change the RDS instance to be publicly accessible

Question 10

A company has an Amazon RDS for PostgreSQL instance that is running out of storage. The database is 2 TB in size and growing at 10 GB per day. They need a solution that allows automatic storage scaling with minimal downtime. What should they do?

Accepted Answer

Enable Storage Auto Scaling. Amazon RDS Storage Auto Scaling automatically increases storage when free space drops below a threshold, with no downtime. For a 2 TB database growing at 10 GB/day, this feature dynamically adds storage in predefined increments (e.g., 5 GB, 10 GB, or 10% of current storage) up to the maximum limit, preventing manual intervention. This directly addresses the requirement for automatic scaling with minimal disruption.

Answer

Purchase reserved instances for cost savings

Answer

Create a read replica and promote it

Answer

Take a manual snapshot and restore to a larger instance

Question 11

Refer to the exhibit. A database administrator runs the AWS CLI command to retrieve CloudWatch metrics for an Amazon RDS DB instance. The output shows a spike in WriteLatency at 10:05 UTC. What is the most likely cause of this spike?

Accepted Answer

The DB instance's gp2 volume has exhausted its burst credits.. A sudden spike in write latency often indicates that the storage volume has exhausted its burst credits and is now using baseline performance, which may be slower. Option B is incorrect because taking a snapshot causes I/O suspension, not necessarily a latency spike. Option C is incorrect because a large number of concurrent connections typically causes increased CPU and memory usage, not a latency spike. Option D is incorrect because a Multi-AZ failover would cause a brief downtime, not a latency spike.

Answer

The DB instance is in the process of taking a snapshot.

Answer

There is a large number of concurrent connections to the DB instance.

Answer

The DB instance experienced a Multi-AZ failover.

Question 12

A company is using Amazon Redshift for data warehousing. The data engineering team notices that queries are running slower than expected. CloudWatch shows that 'CPUUtilization' is high and 'DiskSpaceUsage' is also high. The cluster has 4 dc2.large nodes. What is the most likely cause of the performance degradation?

Accepted Answer

Queries are spilling to disk due to insufficient memory. High CPU and high disk space usage on dc2.large nodes are classic signs of queries spilling to disk due to insufficient memory. When there isn't enough memory for query processing, Redshift resorts to writing intermediate results to disk, which increases disk space usage and also causes high CPU as the system manages the spill. Option A is insufficient network bandwidth: network bandwidth issues would typically manifest as increased network throughput or latency metrics, not high CPU and disk usage. Option B is CPU bottleneck: while CPU is high, the simultaneous high disk usage suggests the root cause is memory spilling, not CPU exhaustion alone. Adding compute nodes would not address the memory spilling if the workload is memory-intensive; instead, increasing the node size or using a different instance type with more memory per node would help. Option C is WLM queue: WLM queue waits would be visible in CloudWatch metrics like 'WLMQueueLength' or 'QueryWaitTime', not in CPU or disk usage.

Answer

Insufficient network bandwidth between nodes

Answer

CPU is the bottleneck and needs more compute nodes

Answer

Workload management (WLM) queue is causing query waits

Question 13

A company is running a MongoDB workload on-premises and wants to migrate to AWS with minimal operational overhead. The application uses MongoDB-specific features like aggregation pipelines. Which service is best?

Accepted Answer

Amazon DocumentDB. Amazon DocumentDB is the correct choice because it is a fully managed, MongoDB-compatible document database that supports MongoDB-specific features like aggregation pipelines, indexes, and queries. It minimizes operational overhead by handling hardware provisioning, patching, backups, and replication, making it ideal for migrating an on-premises MongoDB workload to AWS without significant application changes.

Answer

Amazon DynamoDB

Answer

Amazon RDS for PostgreSQL

Answer

Amazon Elasticsearch Service

Question 14

Which TWO of the following are required when migrating an on-premises Oracle database to Amazon RDS for Oracle using AWS DMS with change data capture (CDC)? (Select TWO.)

Accepted Answer

Use AWS SCT to assess schema compatibility.. AWS SCT (Schema Conversion Tool) is required to assess and convert the source Oracle schema to a format compatible with Amazon RDS for Oracle, ensuring that data types, indexes, and other objects are correctly mapped before migration. This step is critical because even though both are Oracle databases, differences in version, parameter settings, and storage engines can cause schema incompatibilities that DMS cannot handle automatically.

Answer

Create a full backup of the source database.

Answer

Set up Oracle Data Guard for replication.

Answer

Manually create target tables in RDS.

Question 15

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database uses Oracle Data Pump for export/import. The migration must be completed within a short maintenance window. Which migration approach should they use?

Accepted Answer

Use AWS Database Migration Service with full load and change data capture (CDC).. AWS Database Migration Service (DMS) with full load and change data capture (CDC) is the correct approach because it minimizes downtime by performing an initial full load of the Oracle database and then continuously replicating ongoing changes until the cutover, allowing the migration to complete within a short maintenance window. Unlike Oracle Data Pump, which requires the source database to be offline during export/import, DMS with CDC keeps the source operational and only requires a brief outage at final cutover.

Answer

Use AWS Snowball to transfer the database files to AWS and then restore to RDS.

Answer

Use Oracle Data Pump to export the database and import into RDS.

Answer

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

Question 16

A gaming company uses Amazon DynamoDB to store player profiles with partition key player_id. The access pattern is to retrieve profiles for multiple players in a single request. The application currently makes separate GetItem calls, causing high latency. Which design pattern reduces latency and cost?

Accepted Answer

Use BatchGetItem to retrieve multiple items in one request. BatchGetItem allows you to retrieve up to 100 items or 16 MB of data from multiple tables in a single API call, reducing the number of network round trips compared to individual GetItem calls. This directly addresses the high latency caused by multiple sequential requests and also reduces cost because you pay for read capacity units (RCUs) based on the total item size, not per request overhead.

Answer

Enable DynamoDB Accelerator (DAX)

Answer

Redesign to a single-table design

Answer

Create a global secondary index on player_id

Question 17

A company is migrating an on-premises MySQL database to Amazon RDS for MySQL. The database is 500 GB in size and has a 24-hour maintenance window. Which AWS service or tool should be used for the initial data transfer with minimal downtime?

Accepted Answer

AWS Database Migration Service (DMS). AWS Database Migration Service (DMS) is the correct choice because it supports ongoing replication from a source MySQL database to Amazon RDS for MySQL, allowing you to perform a full load followed by continuous change data capture (CDC) to minimize downtime. With a 500 GB database and a 24-hour maintenance window, DMS can complete the initial load and then keep the target in sync until you cut over, achieving near-zero downtime.

Answer

Amazon S3 with AWS Glue

Answer

AWS Snowball Edge

Answer

mysqldump and restore to RDS

Question 18

A company has a high-traffic e-commerce application that uses Amazon RDS for MySQL. During flash sales, the database experiences high read load causing slow page loads. The application is read-heavy with occasional writes. Which design change would provide the most immediate performance improvement?

Accepted Answer

Create read replicas of the RDS instance. Creating read replicas of the RDS instance offloads SELECT queries from the primary database, directly addressing the high read load during flash sales. Read replicas are asynchronous copies that can serve read traffic, reducing the burden on the primary instance and improving page load times for read-heavy workloads.

Answer

Add an Amazon ElastiCache layer

Answer

Enable Multi-AZ deployment

Answer

Upgrade to a larger instance type

Question 19

A database administrator runs the command shown in the exhibit to create a read replica in us-west-2 from a source DB instance in us-east-1. The command fails. What is the most likely cause?

Accepted Answer

The source DB instance does not have backup retention enabled.. The command fails because creating a cross-Region read replica requires the source DB instance to have automated backups enabled (backup retention period > 0). Without backups, Amazon RDS cannot generate the necessary transaction logs to replicate data to the replica in us-west-2. This is a prerequisite for any read replica creation, whether in the same Region or across Regions.

Answer

The source DB instance is not publicly accessible.

Answer

The replica instance class db.r5.large is not available in us-west-2.

Answer

The replica must use the same DB instance class as the source.

Question 20

A company is deploying a new Amazon RDS for SQL Server DB instance with Multi-AZ. The database will be used by a critical application that requires minimal downtime during failover. The application uses a single connection string with the CNAME of the RDS endpoint. During a recent failover test, the application experienced a 3-minute timeout. The DBA wants to reduce the failover time. The current RDS instance is db.r5.large with 100 GB gp2 storage. The application is hosted on EC2 in the same VPC. Which change would MOST effectively reduce the failover time?

Accepted Answer

Configure the application to use a low TTL for DNS lookups and implement connection retries. The most effective because the 3-minute timeout during failover is likely due to DNS caching on the application side. By configuring the application to use a low TTL (e.g., 5 seconds) for DNS lookups and implementing connection retries with exponential backoff, the application can quickly resolve the new RDS endpoint's IP address after failover and re-establish connectivity promptly. Option A is incorrect because changing to Provisioned IOPS (io1) improves storage performance but does not reduce DNS-related failover time. Option B is incorrect because increasing the instance size does not directly impact failover duration. Option D is incorrect because Multi-AZ already provides automatic failover; a read replica with manual promotion would not reduce failover time and would require additional management.

Answer

Change the storage to Provisioned IOPS (io1)

Answer

Change the instance type to db.r5.xlarge

Answer

Use a read replica with automatic failover