DBS-C01 Mock Exam 80 — 25 Questions

Question 1

A company is migrating an on-premises MongoDB database to Amazon DocumentDB (with MongoDB compatibility). The application uses MongoDB's aggregation pipeline with $lookup and $unwind stages. What should the company verify before migration?

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

Accepted Answer

Check if all aggregation pipeline stages used by the application are supported in DocumentDB.. Amazon DocumentDB (with MongoDB compatibility) does not support all MongoDB aggregation pipeline stages. Specifically, the `$lookup` and `$unwind` stages are supported, but other stages like `$merge`, `$facet`, `$bucket`, `$bucketAuto`, `$graphLookup`, and `$search` are not. Before migration, the company must verify that every stage used in their application's aggregation pipelines is fully supported in DocumentDB to avoid runtime failures.

Answer

Verify that DocumentDB supports sharding for the collection.

Answer

Ensure the application uses the latest MongoDB driver.

Answer

Confirm that the application's secondary indexes can be migrated.

Question 2

A company is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The database is used for a financial application that requires complex joins and transactions. Which migration strategy is MOST appropriate?

Accepted Answer

Use AWS SCT to convert the schema and AWS DMS to migrate data. AWS Schema Conversion Tool (SCT) is required to convert the Oracle schema (including complex joins and transaction logic) to a PostgreSQL-compatible format, and AWS Database Migration Service (DMS) performs the ongoing data migration with minimal downtime. This combination handles both schema transformation and data replication for heterogeneous migrations, which is essential for a financial application with complex joins and transactions.

Answer

Use AWS DMS with native Oracle to PostgreSQL endpoint

Answer

Use Oracle GoldenGate to replicate data to Aurora PostgreSQL

Answer

Use pg_dump to export the Oracle database and restore to Aurora PostgreSQL

Question 3

A company is designing a highly available e-commerce application using Amazon DynamoDB. The application requires strongly consistent reads for inventory data and eventual consistency for user session data. Which TWO design decisions should the company make?

Accepted Answer

Use strongly consistent reads for the inventory table by setting ConsistentRead=true in the query.. DynamoDB supports strongly consistent reads by setting the `ConsistentRead=true` parameter in the GetItem, Query, or Scan API calls. This ensures that the application always reads the most recent write, which is critical for inventory data where accuracy is paramount. Strongly consistent reads come at the cost of higher latency and lower throughput compared to eventually consistent reads, but they meet the requirement for inventory consistency.

Answer

Enable DynamoDB Streams on the inventory table to replicate data for disaster recovery.

Answer

Use DynamoDB Accelerator (DAX) for the inventory table to provide strongly consistent reads.

Answer

Use a single DynamoDB table for both inventory and session data with different partition keys.

Question 4

An e-commerce application uses Amazon Aurora MySQL. During a flash sale, the database experiences a surge in write operations, and the application reports 'Lock wait timeout exceeded' errors. The DBA suspects a long-running transaction is blocking others. Which AWS tool or feature should the DBA use to identify the blocking transaction?

Accepted Answer

Amazon Aurora Performance Insights with the 'Wait for lock' dimension. Amazon Aurora Performance Insights with the 'Wait for lock' dimension can identify blocking sessions by showing which sessions are waiting on locks and which session holds the lock. Option B (Amazon Inspector) is a security assessment tool and does not provide database lock information. Option C (CloudWatch Logs Insights) can analyze logs but does not directly identify blocking transactions. Option D (Amazon RDS Enhanced Monitoring) provides OS-level metrics, not database-level lock information.

Answer

Amazon Inspector

Answer

CloudWatch Logs Insights

Answer

Amazon RDS Enhanced Monitoring

Question 5

Refer to the exhibit. A developer reports that the RDS MySQL instance 'mydb' is experiencing high write latency. The storage is gp2 with 100 GB. What is the MOST likely cause of the write latency?

Accepted Answer

The gp2 volume size is too small, resulting in insufficient baseline IOPS. The gp2 volume's baseline IOPS are determined by the volume size at a ratio of 3 IOPS per GB, up to 16,000 IOPS. With a 100 GB gp2 volume, the baseline IOPS is only 300 (100 × 3). This is insufficient for write-heavy workloads, causing write latency as the volume exhausts its IOPS credit balance and enters a throttled state. Burst credits can temporarily boost performance, but sustained high write throughput will deplete credits and lead to latency.

Answer

There is a read replica causing replication lag

Answer

The instance class db.r5.large does not provide enough memory

Answer

Multi-AZ is not enabled, causing synchronous replication overhead

Question 6

A company uses Amazon DynamoDB for a session management system. They need to store session data with a TTL of 24 hours. However, they notice that expired items are not being deleted promptly, causing storage costs to increase. What is the most likely cause?

Accepted Answer

DynamoDB typically deletes expired items within 48 hours. DynamoDB's TTL mechanism typically deletes expired items within 48 hours, not immediately. The service processes TTL deletions as a background process, and while items are marked as expired at the TTL time, actual deletion can be delayed up to 48 hours. This explains why expired session data persists and increases storage costs despite TTL being properly configured.

Answer

The table has insufficient write capacity

Answer

TTL is not enabled on the table

Answer

The TTL attribute is set as a string instead of a number

Question 7

A company runs a financial application that requires ACID transactions on a relational database. The workload has a high volume of writes and reads, and the team wants to minimize operational overhead. Which AWS database service should they choose?

Accepted Answer

Amazon Aurora (MySQL-compatible). Amazon Aurora (MySQL-compatible) is the correct choice because it provides full ACID transaction support required for a financial application, while delivering high throughput for both reads and writes through its distributed, SSD-backed storage architecture. Aurora also minimizes operational overhead by automating tasks like replication, backups, and failover, and it offers up to 5x the throughput of standard MySQL without requiring manual sharding or tuning.

Answer

Amazon RDS for Oracle

Answer

Amazon DynamoDB with transactions enabled

Answer

Amazon ElastiCache for Memcached

Question 8

A company uses Amazon RDS for MySQL with a Multi-AZ deployment. During a recent failover, the application experienced a 2-minute downtime because it was connecting to the primary instance endpoint. The company needs to reduce failover downtime to under 30 seconds. What should be done?

Accepted Answer

Use the Multi-AZ DB cluster endpoint instead of the instance endpoint.. The Multi-AZ DB cluster endpoint provides a single DNS name that automatically routes connections to the current writer instance, eliminating the need for application-side reconnection logic. During a failover, the endpoint updates its DNS record to point to the new primary within seconds, reducing downtime to under 30 seconds. This is the recommended approach for minimizing failover disruption in Multi-AZ deployments.

Answer

Implement Amazon ElastiCache to cache database connections.

Answer

Increase the instance size to improve failover speed.

Answer

Deploy a read replica and promote it manually during failover.

Question 9

A company is running a MySQL database on an EC2 instance and wants to migrate to Amazon RDS for MySQL with minimal downtime. The database is 500 GB in size and has a high write workload. Which migration approach is most appropriate?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication.. AWS DMS with ongoing replication (change data capture) is the most appropriate approach because it allows you to migrate the 500 GB database with minimal downtime. DMS performs a full load of the existing data and then continuously replicates ongoing changes from the source MySQL EC2 instance to the target Amazon RDS for MySQL, enabling a cutover with only a brief pause in writes.

Answer

Export data to Amazon S3 and use AWS Glue to load into RDS.

Answer

Copy the MySQL data directory to Amazon EBS and attach to RDS.

Answer

Take a mysqldump from the source and import into RDS.

Question 10

A company is using Amazon RDS for SQL Server with Multi-AZ. The application experiences a brief interruption during a planned maintenance window. The DBA wants to verify that the failover occurred correctly. Which set of metrics should the DBA examine?

Accepted Answer

DatabaseConnections and ReplicaLag. During a Multi-AZ failover, DatabaseConnections drop to zero as existing connections are terminated, then rise again as applications reconnect. ReplicaLag, which measures the delay between primary and standby, becomes zero after failover because the former standby is now the primary. Monitoring these two metrics together provides clear evidence of a failover event. Option A (FreeStorageSpace) does not change during failover. Option C (WriteIOPS and ReadIOPS) may fluctuate but are not direct indicators of failover. Option D (NetworkThroughput) may also vary but is not a specific failover indicator.

Answer

FreeStorageSpace on the primary instance

Answer

WriteIOPS and ReadIOPS for both instances

Answer

NetworkThroughput on the replica instance

Question 11

Refer to the exhibit. An application team notices that the MySQL RDS instance 'mydb' is running at 80% CPU utilization during peak hours. They need to improve read performance without increasing the CPU load on the primary instance. Which action should they take?

Accepted Answer

Create a Read Replica in the same region. Creating a Read Replica offloads read traffic from the primary MySQL RDS instance, reducing CPU load on the primary while improving read performance for applications. Read Replicas asynchronously replicate data using MySQL’s native binlog-based replication, allowing the primary to focus on write operations without additional CPU overhead from serving reads.

Answer

Increase the DB instance class to db.r5.xlarge

Answer

Change storage type to io1 with higher IOPS

Answer

Enable Multi-AZ deployment

Question 12

A company is building a mobile application that requires users to be able to query their order history quickly. The data is stored in Amazon DynamoDB, and each user has up to 10,000 orders over time. The application needs to support pagination and filtering by order date. What is the MOST efficient way to model this data in DynamoDB?

Accepted Answer

Use user ID as the partition key and order date as the sort key. Using user ID as the partition key ensures all orders for a user are co-located on a single partition, enabling efficient queries. Adding order date as the sort key allows the application to filter and paginate by date range using the Query API with KeyConditionExpression, which is far more efficient than scanning or using a secondary index.

Answer

Scan the entire table and filter on user ID

Answer

Store all orders as a JSON document in a single item per user

Answer

Use user ID as the partition key and a Global Secondary Index on order date

Question 13

A company is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The database is 1 TB and has complex stored procedures. The migration must be completed within a 4-hour downtime window. Which migration approach is most efficient?

Accepted Answer

Use AWS SCT to convert schema and code, then AWS DMS for data migration.. AWS SCT converts the Oracle schema and complex stored procedures to Aurora PostgreSQL-compatible code, while AWS DMS performs the full data migration within the 4-hour window. This combination handles both schema/code conversion and bulk data transfer efficiently, meeting the time constraint.

Answer

Use AWS Schema Conversion Tool (SCT) to convert schema only.

Answer

Use Oracle Data Pump to export and pg_restore to import.

Answer

Use AWS DMS with ongoing replication.

Question 14

A company has a critical application that uses Amazon RDS for MySQL with Multi-AZ deployment. During a recent failure, the automatic failover took 2 minutes, causing application timeout. The company needs to reduce failover time to under 30 seconds. Which solution should the database specialist recommend?

Accepted Answer

Migrate the database to Amazon Aurora MySQL.. Amazon Aurora MySQL is designed to reduce failover time significantly compared to standard RDS MySQL Multi-AZ. Aurora typically completes failover in under 30 seconds by using a shared distributed storage volume across multiple Availability Zones, allowing the primary instance to fail over to a read replica without the need to replay redo logs or perform crash recovery. This meets the requirement of reducing failover time to under 30 seconds.

Answer

Create a read replica and promote it during failover.

Answer

Increase the DB instance class to a larger size.

Answer

Implement Amazon RDS Proxy to handle connection draining.

Question 15

A company needs a database for a serverless web application that stores user sessions. The sessions expire after 24 hours. The database must be highly available and require no server management. Which AWS service is most appropriate?

Accepted Answer

Amazon DynamoDB with TTL.. Amazon DynamoDB with TTL is the most appropriate choice because it provides a fully managed, serverless, highly available NoSQL database that can automatically expire user sessions after 24 hours using the Time to Live (TTL) feature. DynamoDB's on-demand capacity mode eliminates server management, and its built-in replication across multiple Availability Zones ensures high availability without any manual intervention.

Answer

Amazon ElastiCache for Redis with cluster mode.

Answer

Amazon RDS for PostgreSQL with Multi-AZ.

Answer

Amazon S3 with lifecycle policies.

Question 16

A company is designing a database for an analytics workload that requires storing 5 TB of data and running complex SQL queries with joins. The workload is read-heavy and requires high concurrency. Which TWO services are suitable for this workload? (Choose two.)

Accepted Answer

Amazon RDS for MySQL with read replicas. Amazon RDS for MySQL with read replicas is suitable because the workload is read-heavy and requires high concurrency. Read replicas offload SELECT traffic from the primary instance, allowing complex SQL queries with joins to scale horizontally while maintaining ACID compliance for the 5 TB dataset.

Answer

Amazon ElastiCache for Redis

Answer

Amazon DynamoDB

Answer

Amazon S3

Question 17

A company needs to implement a database solution for a global e-commerce platform that requires strongly consistent reads and writes with automatic failover across AWS Regions. Which service should be used?

Accepted Answer

Amazon Aurora Global Database.. Amazon Aurora Global Database is the correct choice because it provides strongly consistent reads and writes across multiple AWS Regions with automatic failover. It uses a primary cluster in one Region and up to five secondary read-only clusters in other Regions, with replication typically under one second. Failover to a secondary Region can be promoted in as little as one minute, meeting the requirements for a global e-commerce platform.

Answer

Amazon DynamoDB global tables.

Answer

Amazon RDS for MySQL with Multi-AZ and cross-Region read replicas.

Answer

Amazon ElastiCache for Redis with Global Datastore.

Question 18

Which TWO actions should be taken to protect sensitive data in an Amazon RDS for Oracle DB instance? (Choose two.)

Accepted Answer

Use Oracle Transparent Data Encryption (TDE) for sensitive columns.. The correct answers are C and E. Option C, using Oracle Transparent Data Encryption (TDE), encrypts sensitive data at the column level within the database. Option E, enabling encryption at rest using AWS KMS, protects data stored on disk. Option A is incorrect because storing credentials in application configuration files is insecure. Option B is incorrect because disabling automated backups does not enhance security. Option D is incorrect because assigning a public IP increases exposure to attacks.

Answer

Store database credentials in the application configuration file.

Answer

Disable automated backups to reduce storage costs.

Answer

Assign a public IP address to the DB instance for easier access.

Question 19

A developer is troubleshooting an application that writes to an Amazon ElastiCache for Redis cluster. The application occasionally fails with 'OOM command not allowed when used memory > maxmemory'. What is the most likely cause?

Accepted Answer

The cluster's maxmemory-policy is set to noeviction.. The error 'OOM command not allowed when used memory > maxmemory' occurs when Redis has reached its configured memory limit and the eviction policy is set to 'noeviction', which prevents any further writes. Option B is correct because 'noeviction' causes Redis to return an error instead of evicting keys. Option A is incorrect because the 'maxclients' limit produces a different error ('max number of clients reached'). Option C is incorrect because keyspace notifications do not affect memory limits. Option D is incorrect because cross-slot commands relate to cluster mode, not memory errors.

Answer

The cluster's maxclients limit has been reached.

Answer

The cluster has too many keyspace notifications enabled.

Answer

The cluster is in cluster mode and cross-slot commands are used.

Question 20

A company is using Amazon Redshift and has a query that is running slowly. The DBA wants to identify if the query is I/O-bound. Which TWO metrics from Amazon CloudWatch can indicate I/O-bound queries?

Accepted Answer

ReadIOPS. Options B and E are correct. ReadIOPS measures the number of read I/O operations per second, and ReadLatency measures the average time per read I/O operation. High values for these metrics indicate that the query is I/O-bound. Option A (NetworkReceiveThroughput) measures network throughput, not I/O. Option C (CPUUtilization) indicates CPU-bound workloads. Option D (WriteIOPS) measures write I/O, which is less likely to be the primary indicator for a slow query, and the question asks for the two metrics that can indicate I/O-bound queries; ReadIOPS and ReadLatency are the most direct I/O metrics.

Answer

NetworkReceiveThroughput

Answer

CPUUtilization

Answer

WriteIOPS