DBS-C01 Practice Exam 54 — 20 Questions

Question 1

Refer to the exhibit. A database engineer runs the command and receives the above output. The engineer wants to convert the database to Multi-AZ. Which command should be used?

Accepted Answer

aws rds modify-db-instance --db-instance-identifier mydb --multi-az. 'aws rds modify-db-instance' with the '--multi-az' flag modifies an existing DB instance to use Multi-AZ deployment. Option A is incorrect because 'reboot-db-instance' with '--force-failover' triggers a reboot and failover but does not change the Multi-AZ setting itself. Option B is incorrect because 'create-db-instance' is used to create a new instance, not modify an existing one. Option D is incorrect because 'create-db-cluster' is for creating an Aurora DB cluster, not for converting a single DB instance to Multi-AZ.

Answer

aws rds reboot-db-instance --db-instance-identifier mydb --force-failover

Answer

aws rds create-db-instance --db-instance-identifier mydb --multi-az

Answer

aws rds create-db-cluster --db-instance-identifier mydb --multi-az

Question 2

A database engineer is troubleshooting an Amazon Aurora MySQL DB cluster that is experiencing frequent failovers. The failovers are occurring during periods of low write activity. The engineer notices that the primary instance's writer endpoint is being used for read traffic from a legacy application. What is the most likely cause of the failovers?

Accepted Answer

The primary instance is overloaded due to read traffic from the writer endpoint. Using the writer endpoint for read traffic can overload the primary instance, leading to resource contention and failovers even during low write activity. Option A is incorrect because replication lag is not a direct cause of failovers; failovers are typically due to primary instance issues. Option B is incorrect because a long-running write transaction would not cause failovers during low write activity; it might cause replication lag but not failover. Option C is incorrect because insufficient storage for the Aurora cluster volume would cause storage-related errors, not failovers; Aurora automatically scales storage.

Answer

A high replication lag between the primary and replica instances

Answer

A long-running write transaction is blocking the failover

Answer

Insufficient storage for the Aurora cluster volume

Question 3

A social media company stores user posts in a database. Each post has a unique ID, content, and timestamp. The application frequently queries posts by user ID and also needs to support a global feed sorted by timestamp. Which database design is most efficient?

Accepted Answer

Amazon DynamoDB with user_id as partition key and timestamp as sort key, plus a GSI on timestamp. It uses user_id as the partition key and timestamp as the sort key for efficient per-user queries, while the Global Secondary Index (GSI) on timestamp allows the global feed to be sorted by timestamp without a costly scan. This design leverages DynamoDB's key-value and query capabilities to support both access patterns with low latency and minimal read capacity consumption.

Answer

Amazon DynamoDB with a single table and scan operation for the global feed

Answer

Amazon S3 with a metadata index in DynamoDB

Answer

Amazon RDS for PostgreSQL with indexes on user_id and timestamp

Question 4

A company is using Amazon ElastiCache for Redis as a caching layer. The application performance degrades when cache misses increase. Which metric should be monitored to track the cache hit rate?

Accepted Answer

CacheHits and CacheMisses. CacheHits and CacheMisses. The cache hit rate is calculated as CacheHits / (CacheHits + CacheMisses), so monitoring both metrics is essential. Option A (CurrConnections) tracks active connections, not hit rate. Option C (CPUUtilization) reflects resource usage. Option D (Evictions) indicates memory pressure but does not directly measure hit rate.

Answer

CurrConnections

Answer

CPUUtilization

Answer

Evictions

Question 5

A company is migrating a large Oracle Data Warehouse (10 TB) to Amazon Redshift. The current system uses complex stored procedures, materialized views, and window functions. The company wants to minimize migration effort. Which approach is MOST suitable?

Accepted Answer

Migrate to Amazon Redshift and rewrite stored procedures as SQL scripts.. Amazon Redshift is purpose-built for large-scale data warehousing and analytics, making it the natural target for a 10 TB Oracle Data Warehouse. While stored procedures would need to be rewritten as SQL scripts (since Redshift uses a different procedural language), materialized views and window functions are natively supported, minimizing migration effort compared to other options.

Answer

Migrate to Amazon Aurora MySQL and use its parallel query feature.

Answer

Migrate to Amazon DynamoDB and use DAX for caching.

Answer

Migrate to Amazon RDS for PostgreSQL and use its foreign data wrappers.

Question 6

Which TWO of the following are valid actions to take when an Amazon Redshift query is taking longer than expected due to disk-based operations?

Accepted Answer

Redistribute data across nodes using a distribution style that minimizes data movement.. (redistributing data with appropriate distribution style) helps minimize data movement across nodes, reducing disk-based operations like spills. Option E (increasing nodes) adds more memory and CPU, enabling more in-memory processing and reducing disk spills. Option A is incorrect because column compression reduces storage but does not prevent disk-based operations. Option B is incorrect because WLM queues manage concurrency, not query speed. Option D is incorrect because sort keys affect order-based optimizations but not disk spills.

Answer

Use column compression to reduce the amount of data scanned.

Answer

Increase the number of workload management (WLM) query queues.

Answer

Change the sort keys to match the query's ORDER BY clause.

Question 7

A DBA runs the IAM policy simulation above. The DBA can describe the DB instance but cannot modify it. What is the most likely cause?

Accepted Answer

An IAM policy explicitly denies the rds:ModifyDBInstance action.. The simulation shows that the DBA can describe the DB instance but cannot modify it. Since the simulation evaluates all applicable IAM policies, an explicit deny for rds:ModifyDBInstance in any attached policy will override any allow and cause the modify action to fail. This is the most likely cause because explicit denies are evaluated first and cannot be overridden by other policies.

Answer

The resource ARN in the simulation is incorrect.

Answer

The DBA's IAM policy does not include an allow for rds:ModifyDBInstance.

Answer

The DBA is not within the VPC where the DB instance resides.

Question 8

A database engineer is reviewing Amazon RDS for MySQL error logs and sees repeated authentication failures from the same IP address. The application team confirms the password is correct. What is the most likely cause of these errors?

Accepted Answer

The user 'app_user' does not have access from host '10.0.1.50'. The error logs show authentication failures despite the password being correct, which indicates the issue is not with the password itself but with the host-based access control. In MySQL, user accounts are defined as 'user'@'host', and if the application is connecting from an IP address (e.g., 10.0.1.50) that is not included in the user's allowed hosts, MySQL will reject the connection with an authentication error even if the password is correct. This is a common misconfiguration when migrating or scaling applications across different subnets.

Answer

The password is incorrect

Answer

The 'app_user' account is locked

Answer

The database requires SSL connections

Question 9

A startup is building a social media application that requires a database to store user relationships (followers, following) and support graph queries. The data volume is expected to grow to tens of terabytes. Which AWS database service is most suitable for this workload?

Accepted Answer

Amazon Neptune.. Amazon Neptune is a fully managed graph database service optimized for storing and querying highly connected data, such as social media user relationships (followers, following). It supports both property graph and RDF models, enabling efficient graph traversal queries using Gremlin or SPARQL, which is ideal for this workload. Neptune scales to tens of terabytes and provides low-latency query performance for complex graph patterns, making it the most suitable choice.

Answer

Amazon RDS for MySQL with self-joins.

Answer

Amazon Redshift.

Answer

Amazon DynamoDB with adjacency list design.

Question 10

A company is running an Amazon DocumentDB cluster. The application is experiencing high write latency. The cluster has a single instance. What should be done to identify the cause of the latency?

Accepted Answer

Enable Performance Insights and review the top wait events.. Enabling Performance Insights for Amazon DocumentDB allows you to monitor the database load and review top wait events, which helps identify the specific causes of high write latency, such as lock contention or I/O bottlenecks. Option A is wrong because simply upgrading to a larger instance size addresses symptoms but does not identify the root cause. Option C is wrong because adding a replica does not reduce write latency on the primary instance; it only offloads read traffic. Option D is wrong because changing to Provisioned IOPS may improve I/O performance but does not diagnose the underlying issue causing latency.

Answer

Upgrade the instance to a larger size.

Answer

Add a replica to distribute the write load.

Answer

Change the storage type to Provisioned IOPS.

Question 11

A company is using Amazon DynamoDB with fine-grained access control using IAM policies. The security team wants to ensure that a specific IAM role can only read the 'status' attribute from items in a table. The table is named 'Orders'. Which IAM policy statement should be used?

Accepted Answer

Condition: { 'ForAllValues:StringEquals': { 'dynamodb:Attributes': ['status'] } }. It uses the `dynamodb:Attributes` condition key with `ForAllValues:StringEquals` to restrict the request to only access the 'status' attribute. This ensures the role can only read the 'status' attribute, meeting the requirement. Option A incorrectly uses the condition to match the literal value 'active' as an attribute name. Options C and D use invalid or irrelevant condition keys.

Answer

Condition: { 'ForAllValues:StringEquals': { 'dynamodb:Attributes': ['active'] } }

Answer

Condition: { 'ForAllValues:StringEquals': { 'dynamodb:ReturnValues': 'ALL_OLD' } }

Answer

Condition: { 'StringEquals': { 'dynamodb:Select': 'SPECIFIC_ATTRIBUTES' } }

Question 12

A company is migrating its on-premises Oracle database to Amazon RDS for Oracle. The database specialist needs to monitor the migration process and ensure data consistency. Which TWO AWS services should be used together to continuously monitor the replication lag and data integrity?

Accepted Answer

AWS Database Migration Service (AWS DMS). AWS DMS is the correct service because it is specifically designed for database migrations and provides built-in monitoring of replication lag via the 'CDC latency' metric. Amazon CloudWatch is the correct complementary service because it collects and visualizes DMS metrics, including replication lag and task status, and can trigger alarms if data integrity or latency thresholds are breached.

Answer

Amazon RDS Performance Insights

Answer

AWS Schema Conversion Tool (AWS SCT)

Answer

AWS Glue

Question 13

A company is designing a security strategy for Amazon RDS for SQL Server. Which TWO actions should be taken to encrypt data at rest? (Choose TWO.)

Accepted Answer

Enable Transparent Data Encryption (TDE) on the SQL Server database.. For Amazon RDS for SQL Server, encryption at rest can be achieved using two methods: enabling RDS encryption at rest with AWS KMS (option E) or enabling Transparent Data Encryption (TDE) natively within SQL Server (option B). Option A is incorrect because EBS encryption is automatically handled by RDS when you enable encryption at rest via KMS, but you cannot enable EBS encryption directly on the underlying volumes. Option C is incorrect because AWS CloudHSM can be used for key management but is not required for RDS encryption at rest. Option D is incorrect because SSL/TLS encrypts data in transit, not at rest.

Answer

Enable Amazon EBS encryption on the underlying volumes.

Answer

Use AWS CloudHSM to store encryption keys.

Answer

Enable SSL/TLS for connections.

Question 14

Which TWO are valid considerations when designing a global database with Amazon Aurora Global Database? (Select TWO.)

Accepted Answer

Secondary regions can forward write operations to the primary region.. Amazon Aurora Global Database uses a primary-region architecture where secondary regions are fully readable and can forward write operations to the primary region. This is achieved through a dedicated replication channel that allows secondary clusters to accept write requests and asynchronously forward them to the primary, ensuring low-latency local writes while maintaining global consistency.

Answer

Secondary regions cannot have their own reader instances.

Answer

Failover requires promoting the secondary cluster to a standalone cluster.

Answer

Cross-region replication latency is typically under 100 milliseconds.

Question 15

A gaming company uses Amazon RDS for PostgreSQL to store player profiles and game state data. The database is currently 500 GB and grows by 10 GB per day. The company runs weekly reports that scan the entire database, causing high I/O and CPU usage. The application experiences read latency spikes during report generation. The team wants to minimize performance impact on the application while maintaining the ability to run reports. Which solution should the team implement?

Accepted Answer

Create a read replica and direct all report queries to the read replica.. Creating a read replica for Amazon RDS for PostgreSQL allows the team to offload all report queries to a separate read-only endpoint, eliminating the I/O and CPU contention on the primary database. This directly addresses the read latency spikes during report generation without requiring any application changes beyond redirecting the reporting queries. The read replica asynchronously replicates data from the primary instance, ensuring the reports see a near-real-time snapshot of the data while the primary remains dedicated to the application workload.

Answer

Enable Multi-AZ deployment to provide a standby instance for failover and use it for reporting.

Answer

Scale up the RDS instance to a larger instance type to handle the additional load from reports.

Answer

Archive historical game state data to Amazon S3 and delete it from the database to reduce size.

Question 16

A company uses Amazon DynamoDB and wants to audit access to a table. Which TWO services can be used together to log and monitor data plane operations? (Choose TWO.)

Accepted Answer

Amazon CloudWatch Logs. AWS CloudTrail (option C) can be configured to log data plane operations for DynamoDB, such as GetItem, PutItem, or Query. Amazon CloudWatch Logs (option A) can then be used to store, monitor, and alarm on these logs. Together they provide auditing of data plane access. Options B, D, and E are incorrect: S3 access logs only apply to S3, VPC Flow Logs capture network traffic, and AWS Config records configuration changes, not data operations.

Answer

S3 access logs

Answer

VPC Flow Logs

Answer

AWS Config

Question 17

A company is using Amazon ElastiCache for Redis as a caching layer for a high-traffic web application. The cache hit ratio has dropped from 95% to 70% after a recent deployment that changed the cache key structure. The application team wants to improve the hit ratio without increasing the cache memory. Which action should they take?

Accepted Answer

Implement a consistent hashing algorithm for key distribution.. A drop in cache hit ratio after changing the key structure indicates that the new keys are not being distributed evenly across the cluster nodes, causing some nodes to be overloaded with misses. Implementing a consistent hashing algorithm (e.g., using the Redis Cluster hash slot mechanism or a client-side library like libketama) ensures that keys are distributed uniformly across shards, minimizing cache misses and improving the hit ratio without adding memory.

Answer

Disable Cluster Mode and use a single node.

Answer

Increase the TTL (time-to-live) for all cache keys.

Answer

Use random TTLs to spread out expiration times.

Question 18

A database administrator is monitoring an Amazon RDS for PostgreSQL DB instance. The administrator notices that the DB instance is using more memory than expected. Which TWO metrics in Amazon CloudWatch can help diagnose memory usage?

Accepted Answer

FreeableMemory. The correct answers are FreeableMemory (B) and SwapUsage (E). FreeableMemory reflects the amount of available memory on the instance; a low value indicates high memory usage. SwapUsage tracks the amount of swap space being used; when memory is exhausted, the OS begins swapping, which directly indicates memory pressure. The other metrics are unrelated to memory: NetworkReceiveThroughput (A) measures network traffic, ReadIOPS (C) measures I/O operations, and DatabaseConnections (D) shows the number of connections, not memory consumption.

Answer

NetworkReceiveThroughput

Answer

ReadIOPS

Answer

DatabaseConnections

Question 19

A company is running an Amazon RDS for SQL Server instance and wants to automate the patching of the database engine. Which AWS service should be used?

Accepted Answer

Amazon RDS Maintenance Window. Amazon RDS Maintenance Window is the correct service for automating patching of RDS database engines. RDS automatically applies minor engine version patches during the maintenance window, and you can schedule these windows for automated patching. AWS Systems Manager Patch Manager is not used for RDS database engine patching; it is designed for patching EC2 instances and on-premises servers. AWS Config is for configuration compliance, and RDS Automated Backups handle backups, not patching.

Answer

AWS Config

Answer

Amazon RDS Automated Backups

Answer

AWS Systems Manager Patch Manager

Question 20

A gaming company uses Amazon RDS for PostgreSQL to store player profiles and game state. They report slow queries during peak hours. The DB instance is a db.r5.2xlarge with 500 GB gp2 storage. Which design change would MOST improve read performance for the most frequently accessed player profiles?

Accepted Answer

Add a read replica in the same AZ. Adding a read replica in the same Availability Zone (AZ) offloads read traffic from the primary RDS for PostgreSQL instance, directly improving read performance for frequently accessed player profiles during peak hours. Read replicas asynchronously replicate data using PostgreSQL's streaming replication and can serve SELECT queries without impacting the primary instance's write workload or connection limits.

Answer

Implement application-level sharding by player ID

Answer

Increase provisioned IOPS on the existing volume

Answer

Upgrade to a db.r5.4xlarge instance