DBS-C01 Mock Exam 88 — 25 Questions

Question 1

A company is using AWS Database Migration Service (AWS DMS) to migrate a 5 TB MySQL database to Amazon RDS for MySQL. The migration is taking longer than expected. The company notices that the source database has a high volume of write operations. Which configuration change would MOST likely improve the migration performance?

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

Accepted Answer

Increase the number of parallel threads in the DMS task settings.. Increasing the number of parallel threads in the DMS task settings allows AWS DMS to process multiple table partitions or row changes concurrently, which directly addresses the bottleneck caused by a high volume of write operations on the source. By default, DMS uses a single thread per table, but when the source is under heavy write load, parallel threads can capture and apply changes more efficiently, reducing the overall migration time.

Answer

Enable Multi-AZ on the target RDS instance.

Answer

Use a smaller instance class for the replication instance to reduce cost.

Answer

Set the LOB mode to 'Full LOB mode'.

Question 2

Which TWO of the following are valid considerations when migrating an on-premises Oracle database to Amazon RDS for Oracle using AWS DMS? (Select TWO.)

Accepted Answer

DMS can continue to replicate changes after the full load is complete until the cutover.. AWS DMS supports ongoing replication (change data capture, CDC) after the full load completes, allowing you to keep the target database synchronized with the source until you perform the cutover. This minimizes downtime because you can replicate ongoing changes from the on-premises Oracle database to Amazon RDS for Oracle, then stop all applications and switch over with only a brief interruption.

Answer

DMS automatically converts Oracle stored procedures to RDS for Oracle compatible code.

Answer

DMS automatically converts partitioned tables to non-partitioned tables.

Answer

DMS can migrate directly to Amazon RDS Custom for Oracle without any configuration changes.

Question 3

Which THREE of the following are required to set up cross-Region replication for an Amazon RDS for MySQL DB instance? (Choose THREE.)

Accepted Answer

The source DB instance must be in a VPC.. For cross-Region replication of an Amazon RDS for MySQL DB instance, the source DB instance must have automated backups enabled (option D). This is typically achieved by setting a backup retention period of at least 1 day (option A is not a separate requirement; it is the mechanism to enable automated backups). The source DB instance must be in a VPC (option B), and a read replica must be created in the target Region (option C). Multi-AZ deployment (option E) is not required.

Answer

The backup retention period on the source must be at least 1 day.

Answer

The source DB instance must be a Multi-AZ deployment.

Question 4

A company is deploying Amazon DynamoDB for a new application. The application requires single-digit millisecond latency for read operations. Which DynamoDB feature should be configured to meet this requirement?

Accepted Answer

DynamoDB Accelerator (DAX). DynamoDB Accelerator (DAX) is an in-memory caching service that sits between your application and DynamoDB, providing microsecond to single-digit millisecond latency for read-heavy workloads. By caching frequently accessed items, DAX offloads read traffic from the underlying DynamoDB tables, ensuring consistent low-latency responses even under high concurrency.

Answer

DynamoDB Streams

Answer

Auto Scaling

Answer

Time to Live (TTL)

Question 5

A company is using Amazon DynamoDB with on-demand capacity. The application experiences increased latency during peak hours. The DynamoDB table receives about 5,000 writes per second and 10,000 reads per second. The read latency is high, but write latency is acceptable. What should the company do to reduce read latency?

Accepted Answer

Enable DynamoDB Accelerator (DAX) for the table.. DynamoDB Accelerator (DAX) is a fully managed, highly available, in-memory cache that significantly reduces read latency for DynamoDB tables, especially for repeated reads. DAX allows you to offload read traffic from the table and serve read requests from the cache, reducing the load on the table and improving response times. Option A is wrong because DynamoDB Streams is used to capture changes to items in the table, not to cache data or offload read traffic. Option B is wrong because DynamoDB does not support read replicas; DAX is the caching solution for reads. Option D is wrong because switching to provisioned capacity and enabling auto scaling would help with scaling write capacity but does not directly address high read latency; DAX is specifically designed for in-memory caching to improve read performance.

Answer

Enable DynamoDB Streams to offload read traffic.

Answer

Create a read replica of the DynamoDB table.

Answer

Switch to provisioned capacity and enable auto scaling.

Question 6

A company is running an Amazon RDS for SQL Server instance with Multi-AZ deployment. The database is used by a critical application. During a recent failover test, the application experienced a 2-minute downtime. The application's connection string uses the DB instance endpoint, not the cluster endpoint. Which change would minimize downtime during future failovers?

Accepted Answer

Modify the application to use the cluster endpoint instead of the instance endpoint. Using the cluster endpoint (the DNS name that automatically points to the current primary after failover) allows the application to reconnect to the new primary without waiting for DNS propagation, thus minimizing downtime. Option B is incorrect because increasing the DB instance class size does not reduce failover time. Option C is incorrect because read replicas are used for read scaling, not for reducing failover downtime. Option D is incorrect because Multi-AZ is already enabled, so enabling it again would have no effect.

Answer

Increase the DB instance class size

Answer

Create a read replica in a different Availability Zone

Answer

Enable Multi-AZ on the DB instance

Question 7

A company is using Amazon DynamoDB with autoscaling enabled. The table has a partition key of 'order_id' and a sort key of 'order_date'. The application performs both point queries and range queries. Recently, the 'ConsumedReadCapacityUnits' metric shows that the table is consistently using 100% of the provisioned capacity. Which THREE factors should the database engineer investigate to determine the cause?

Accepted Answer

Whether the application is using Scan operations instead of Query operations.. Scan operations read the entire table or index before applying filters, consuming far more read capacity than Query operations, which target specific partition and sort key values. If the application is using Scans instead of Queries, it would consistently consume 100% of provisioned capacity even for small result sets, leading to throttling and high utilization.

Answer

Whether autoscaling is configured correctly to add capacity.

Answer

Whether a global secondary index is being used for queries.

Question 8

Which TWO AWS services can be used to cache database query results to improve read performance? (Select TWO.)

Accepted Answer

Amazon ElastiCache for Redis. Amazon ElastiCache for Redis and Amazon ElastiCache for Memcached are in-memory caching services that can store the results of database queries, allowing subsequent identical queries to be served from the cache instead of hitting the database. This reduces latency and improves read performance by offloading read traffic from the primary database.

Answer

Amazon DynamoDB Accelerator (DAX)

Answer

Amazon CloudFront

Answer

Amazon RDS read replica

Question 9

A company needs to migrate an on-premises PostgreSQL database to Amazon Aurora PostgreSQL. The database is 2 TB in size and has a 24/7 uptime requirement. Which AWS service should be used to perform the migration 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 an on-premises PostgreSQL source to Amazon Aurora PostgreSQL, enabling a migration with minimal downtime. DMS can perform a full load of the 2 TB database and then continuously replicate changes using PostgreSQL's logical replication (via the pglogical extension or native slot-based replication) until the cutover, keeping the source available throughout the process.

Answer

AWS Schema Conversion Tool (SCT)

Answer

AWS S3

Answer

pg_dump and pg_restore

Question 10

A developer is receiving timeout errors when connecting to an Amazon ElastiCache for Redis cluster from an Amazon EC2 instance. The security group for the EC2 instance allows outbound traffic to the Redis cluster's security group on port 6379. The Redis cluster's security group does not allow inbound traffic from the EC2 instance. What is the most likely cause of the timeout?

Accepted Answer

The Redis cluster security group does not have an inbound rule allowing traffic from the EC2 security group on port 6379. Security groups are stateful, meaning that if an outbound rule allows traffic, the return traffic is automatically allowed. However, inbound traffic must be explicitly permitted by the target security group. In this scenario, the EC2 instance's security group allows outbound traffic to the Redis cluster's security group on port 6379, but the Redis cluster's security group does not have an inbound rule allowing traffic from the EC2 security group on that port. Therefore, the connection is blocked, causing timeout errors. Option A is incorrect because network ACLs are stateless and would affect both inbound and outbound traffic, but the issue is specifically with security groups. Option C is incorrect because subnet route tables control network routing, not port-level access. Option D is incorrect because ElastiCache for Redis clusters are accessible within the same VPC if proper security group rules are configured.

Answer

The network ACL for the Redis subnet is blocking inbound traffic on port 6379

Answer

The subnet route table does not have a route to the Redis cluster

Answer

The Redis cluster is not accessible from within the same VPC

Question 11

A company is migrating a MySQL database to Amazon Aurora MySQL. The current database uses multi-statement transactions with read committed isolation level. The application frequently encounters deadlocks on the source database. Which Aurora MySQL feature can help reduce deadlocks without application changes?

Accepted Answer

Use Amazon RDS Proxy to pool and share database connections.. RDS Proxy helps reduce deadlocks by pooling and reusing database connections, which minimizes the overhead of establishing new connections and reduces contention on database resources. In MySQL, deadlocks often occur when multiple transactions compete for the same resources under high connection churn; by maintaining a stable pool of connections, RDS Proxy lowers the probability of concurrent conflicting locks. Since the proxy is transparent to the application, no code changes are required to benefit from this behavior.

Answer

Use Amazon Aurora Auto Scaling to automatically adjust the number of replicas.

Answer

Use Amazon Aurora Global Database to replicate data to multiple regions.

Answer

Use Amazon Aurora Backtrack to quickly revert transactions.

Question 12

A company runs an Amazon Aurora MySQL database cluster with a primary instance and two Aurora Replicas. The application is experiencing occasional deadlocks on the primary instance during peak hours. The deadlocks cause transaction rollbacks that impact customer experience. Which design change should the company implement to minimize deadlocks?

Accepted Answer

Enable Aurora Auto Scaling for read replicas and offload read-only queries to replicas.. Offloading read-only queries to Aurora Replicas reduces the volume of read-write contention on the primary instance. Deadlocks often arise when concurrent transactions compete for the same resources; by directing read traffic to replicas, the primary handles fewer overlapping transactions, lowering the probability of lock conflicts. Aurora Replicas share the same underlying storage volume and serve read traffic without blocking writes on the primary, making this a targeted solution for deadlock reduction.

Answer

Set the transaction isolation level to READ UNCOMMITTED to avoid locks.

Answer

Configure Multi-AZ deployment to automatically failover during deadlocks.

Answer

Increase the DB instance class size to handle more concurrent transactions.

Question 13

Refer to the exhibit. A database administrator has this IAM policy attached to their user. They attempt to delete the database instance 'prod-mydb' but receive an 'AccessDenied' error. Why?

Accepted Answer

The Deny statement explicitly denies deletion of any instance with an identifier starting with 'prod-'.. The IAM policy includes an explicit Deny statement that denies the rds:DeleteDBInstance action when the resource ARN contains an instance identifier starting with 'prod-'. Explicit Deny statements override any Allow statements, so even if another policy allows deletion, this Deny blocks it for instances like 'prod-mydb'.

Answer

The policy does not allow the rds:DeleteDBInstance action for any resource.

Answer

The resource ARN in the Deny statement does not match the instance.

Answer

The user does not have permission to describe the DB instance.

Question 14

A company is designing a database for a global e-commerce platform. The application requires single-digit millisecond read and write latency for user sessions, and must handle millions of requests per second. The data is key-value in nature. Which TWO AWS services should the company consider? (Choose two.)

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is a fully managed NoSQL key-value and document database that delivers single-digit millisecond latency at any scale. It is designed for high-traffic applications requiring millions of requests per second, making it ideal for the global e-commerce platform's user session data.

Answer

Amazon Neptune

Answer

Amazon Redshift

Answer

Amazon RDS for MySQL

Question 15

A company is designing a multi-tenant SaaS application on Amazon Aurora MySQL. Each tenant has its own database, but some tenants are very large and generate high write traffic. The company wants to isolate tenant workloads to prevent a noisy neighbor from affecting other tenants. Which TWO design strategies should the database specialist recommend?

Accepted Answer

Use Aurora Serverless for tenants with variable workloads. Aurora Serverless automatically scales compute capacity based on application demand, which is ideal for tenants with variable workloads. This prevents a noisy neighbor scenario by ensuring that a tenant's burst of write traffic does not consume shared resources that would degrade performance for other tenants.

Answer

Use a single Aurora cluster with read replicas for each tenant

Answer

Migrate all tenants to Amazon DynamoDB and use DynamoDB Accelerator (DAX) for caching

Answer

Use Amazon RDS Proxy to pool connections and limit throughput per tenant

Question 16

A company is running a MongoDB-compatible Amazon DocumentDB cluster. The application team reports that write operations are failing intermittently with a `WriteConcernError` indicating that the write concern could not be satisfied. The cluster has one primary and two replicas. What is the MOST likely cause of this issue?

Accepted Answer

One of the replicas is down or experiencing high replication lag. The WriteConcernError occurs because the write concern requires acknowledgment from a certain number of replicas. With a cluster of one primary and two replicas, if any replica is down or has high replication lag, the write concern requirement cannot be satisfied. Option A is correct because that is the most likely cause. Option B is incorrect because the cluster has enough replicas for majority write concern if all are healthy. Option C is incorrect because read preference does not affect write operations. Option D is incorrect because the primary being overloaded with reads would not cause a WriteConcernError; it would affect performance but not the ability to satisfy write concern.

Answer

The cluster does not have enough replica instances to satisfy the write concern

Answer

The application is using an incorrect read preference

Answer

The primary instance is overloaded with read requests

Question 17

A developer needs to allow an application running on an EC2 instance to read and write data to a DynamoDB table named 'Orders'. The EC2 instance is configured with an IAM role. Which IAM policy should be attached to the role?

Accepted Answer

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "dynamodb:GetItem", "dynamodb:PutItem" ], "Resource": "arn:aws:dynamodb:us-east-1:123456789012:table/Orders" } ] }. The policy grants exactly the required DynamoDB actions (GetItem and PutItem) on the specific 'Orders' table, following the principle of least privilege. Option A is incorrect because it grants full DynamoDB access to all tables, which is overly permissive. Option B is incorrect because it grants EC2 actions, not DynamoDB actions. Option D is incorrect because it grants S3 actions instead of DynamoDB actions.

Answer

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "dynamodb:*", "Resource": "*" } ] }

Answer

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "ec2:*", "Resource": "*" } ] }

Answer

{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": "s3:*", "Resource": "arn:aws:s3:::example-bucket/*" } ] }

Question 18

A company has an Amazon DynamoDB table that stores sensitive user data. The security team requires that all data is encrypted at rest using a customer-managed AWS KMS key. Which step should be taken to meet this requirement?

Accepted Answer

Specify a customer-managed KMS key in the DynamoDB table creation.. You can specify a customer-managed AWS KMS key when creating a DynamoDB table to enable encryption at rest with that key. Option E is incorrect because while you can restrict access to a specific IAM role, the question specifically asks about encryption at rest. Option A is wrong because DynamoDB uses KMS keys, not S3-managed keys. Option B is wrong because bucket policies are for S3, not DynamoDB. Option D is wrong because encryption at rest cannot be enabled after table creation; it must be specified at creation time.

Answer

Enable server-side encryption with S3-managed keys (SSE-S3) on the DynamoDB table.

Answer

Attach a bucket policy to restrict access to the DynamoDB table.

Answer

Modify the existing DynamoDB table to enable encryption at rest.

Answer

Create an IAM policy that allows dynamodb:GetItem and dynamodb:PutItem only when the request is made by the specific IAM role.

Question 19

Refer to the exhibit. A company wants to migrate this RDS MySQL instance to an Aurora MySQL cluster with encryption at rest. What is the most efficient approach?

Accepted Answer

Create a snapshot of the RDS instance, copy the snapshot with encryption, then restore to an Aurora cluster.. It is the most efficient approach to migrate an RDS MySQL instance to an encrypted Aurora MySQL cluster. You first create a snapshot of the RDS instance, then copy that snapshot with encryption enabled (using an AWS KMS key), and finally restore the encrypted snapshot to an Aurora cluster. This method ensures encryption at rest is applied during the migration without requiring additional data transfer or schema conversion.

Answer

Use AWS DMS to migrate the database to an encrypted Aurora cluster.

Answer

Create a snapshot of the RDS instance and restore it directly to an Aurora cluster.

Answer

Create an encrypted read replica in Aurora and promote it.

Question 20

A company is using Amazon RDS for MySQL to power a web application. The database contains sensitive data, and the security team requires that all connections to the database use SSL/TLS. The team has enabled 'require_secure_transport' parameter in the DB parameter group. However, a developer reports that they are able to connect to the database using a MySQL client without specifying SSL options. What could be the reason?

Accepted Answer

The 'require_secure_transport' parameter is not set to '1' in the DB parameter group.. Enabling the 'require_secure_transport' parameter in the DB parameter group requires explicitly setting it to '1'. By default, this parameter is '0' (disabled). Even if the parameter group is associated with the RDS instance, if the parameter value is not set to '1', the database will still accept non-SSL connections. After setting it to '1', the instance must be rebooted for the change to take effect. Option A is incorrect because 'require_secure_transport', when properly configured, rejects non-SSL connections. Option B is incorrect because the MySQL client does not automatically upgrade to SSL; it only uses SSL if explicitly requested or if the client defaults to SSL (which depends on client configuration). Option D is incorrect because connections from within the same VPC are still subject to the database's SSL enforcement settings.

Answer

The RDS instance is configured to accept both SSL and non-SSL connections by default.

Answer

The MySQL client automatically upgrades to SSL when the server requires it.

Answer

The developer is connecting from an EC2 instance in the same VPC, which bypasses SSL enforcement.