DBS-C01 Mock Exam 84 — 25 Questions

Question 1

A company is designing a disaster recovery strategy for an Amazon RDS for PostgreSQL database. They need a Recovery Point Objective (RPO) of less than 5 seconds and a Recovery Time Objective (RTO) of less than 1 minute. Which TWO actions should they take? (Choose two.)

Accepted Answer

Create a cross-region read replica and configure automatic failover using Amazon Route 53 health checks. Option D is correct because a cross-region read replica can be promoted to a primary instance in under a minute, and with Amazon Route 53 health checks configured for automatic failover, the DNS update occurs automatically, meeting the RTO of less than 1 minute. The asynchronous replication lag is typically sub-second, achieving an RPO of less than 5 seconds. Option E is correct because a Multi-AZ deployment with a synchronous standby in another Availability Zone provides automatic failover with no data loss (RPO of 0) and failover completes in about 30-60 seconds, satisfying both RPO and RTO requirements.

Answer

Use AWS Database Migration Service for continuous replication to a separate instance

Answer

Create a cross-region read replica and manually update DNS in a disaster

Answer

Take hourly snapshots and restore in another region

Question 2

A startup needs a cost-effective database for a small application that handles both transactional and analytical workloads. They expect low traffic initially but want the database to automatically scale as the business grows. Which database solution is BEST suited?

Accepted Answer

Amazon Aurora Serverless v2. Amazon Aurora Serverless v2 is the best fit because it automatically scales compute and memory capacity in fine-grained increments (down to 1 ACU) based on actual workload demand, supporting both transactional (OLTP) and analytical (OLAP) queries via the MySQL/PostgreSQL-compatible Aurora engine. It offers a pay-per-ACU model that is cost-effective for low-traffic startups while providing near-instant scaling to handle growth without manual intervention.

Answer

Amazon DynamoDB with on-demand capacity

Answer

Amazon RDS for MySQL with a Single-AZ deployment

Answer

Amazon Redshift Serverless

Question 3

A company is migrating a 5 TB MongoDB database to Amazon DocumentDB. They have a short maintenance window and need to minimize downtime. Which migration strategy should be used?

Accepted Answer

Use AWS DMS to perform a full load and then ongoing replication from the source MongoDB.. AWS DMS supports MongoDB as a source and Amazon DocumentDB as a target, enabling a full load of the 5 TB database followed by ongoing change data capture (CDC) using MongoDB's oplog. This minimizes downtime by keeping the target nearly synchronized during the migration window, allowing a final cutover with minimal interruption.

Answer

Use the MongoDB change streams feature to replicate changes to DocumentDB in real time.

Answer

Set up AWS Direct Connect to the source and use mongorestore directly to DocumentDB.

Answer

Export the data using mongodump, transfer to Amazon S3, and import using mongorestore.

Question 4

A startup is building a real-time leaderboard for a gaming application. The data is highly dynamic with frequent updates and requires single-digit millisecond latency. Which database is most suitable?

Accepted Answer

Amazon DynamoDB. Amazon DynamoDB is the most suitable choice because it is a fully managed NoSQL key-value and document database that delivers single-digit millisecond latency at any scale, making it ideal for real-time leaderboards with high-frequency updates. Its DAX (DynamoDB Accelerator) caching layer can further reduce read latency to microseconds, while its auto-scaling and on-demand capacity modes handle the highly dynamic workload without downtime.

Answer

Amazon Neptune

Answer

Amazon Redshift

Answer

Amazon RDS for PostgreSQL

Question 5

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 6

A company uses Amazon RDS for Oracle with a custom application that generates complex hierarchical queries using CONNECT BY. They want to migrate to Amazon Aurora to reduce licensing costs. Which migration strategy requires the fewest application changes?

Accepted Answer

Migrate to Amazon Aurora PostgreSQL and rewrite hierarchical queries to use recursive CTEs.. Option C is correct because Aurora PostgreSQL supports recursive Common Table Expressions (CTEs) via the WITH RECURSIVE clause, which can be used to rewrite Oracle's CONNECT BY hierarchical queries with minimal application changes. This approach avoids the licensing costs of Oracle while preserving the hierarchical query logic, requiring only a syntax rewrite rather than a complete redesign. Aurora MySQL does not support CONNECT BY or recursive CTEs, making PostgreSQL the only Aurora engine that can handle this workload without significant application restructuring.

Answer

Use AWS Database Migration Service (DMS) to migrate directly to Aurora with no application changes.

Answer

Migrate to Amazon Aurora MySQL and use its hierarchical query features.

Answer

Migrate to Amazon RDS for SQL Server and use its recursive CTEs.

Question 7

A healthcare company stores patient records in Amazon DynamoDB. Each record includes patient_id (partition key), visit_date (sort key), and a large JSON attribute for medical history. The application frequently queries recent visits for a patient and scans historical data for analytics. The scans on the medical history attribute cause high RCU consumption. The company wants to reduce costs and improve query performance. Which design should be implemented?

Accepted Answer

Move the medical history attribute to a separate table with patient_id as partition key and visit_date as sort key. Use DynamoDB Streams to keep both tables in sync.. Option B is correct because it separates the large, infrequently accessed medical history attribute from the frequently queried core record, reducing the item size for common queries and thus lowering RCU consumption. By using DynamoDB Streams to synchronize the two tables, you maintain data consistency without adding complexity to the application, and queries against the main table become faster and cheaper since they no longer read the large JSON payload.

Answer

Compress the medical history attribute using gzip before storing in DynamoDB.

Answer

Enable DynamoDB Accelerator (DAX) for the table to cache frequent queries.

Answer

Use Amazon S3 to store the medical history as a separate object and reference it from DynamoDB.

Question 8

A company is migrating an on-premises Oracle database with complex stored procedures and triggers to AWS. They want to minimize code changes. Which two AWS database services should they consider? (Choose two.)

Accepted Answer

Amazon RDS for Oracle. Amazon RDS for Oracle is a direct migration target for on-premises Oracle databases, supporting the same Oracle Database engine. This minimizes code changes because existing stored procedures, triggers, and PL/SQL code can run with minimal or no modification, leveraging Oracle's native compatibility.

Answer

Amazon DynamoDB

Answer

Amazon S3

Answer

Amazon Redshift

Question 9

Which TWO of the following are advantages of using Amazon Aurora over standard RDS for MySQL?

Accepted Answer

Aurora can deliver up to 5x the throughput of standard MySQL on the same hardware.. Option C is correct because Amazon Aurora uses a distributed, SSD-backed storage subsystem that separates compute from storage, enabling it to deliver up to 5x the throughput of standard MySQL running on the same hardware. This performance gain comes from the Aurora storage engine's ability to reduce I/O operations and parallelize writes across multiple storage nodes.

Answer

Aurora automatically fails over to a read replica in case of primary failure.

Answer

Aurora is compatible with PostgreSQL, so you can migrate from SQL Server easily.

Answer

Aurora supports up to 15 read replicas, while RDS for MySQL only supports 5.

Question 10

A company is migrating a MySQL database from on-premises to Amazon RDS for MySQL. They want to use native MySQL replication to minimize downtime. Which configuration is required in the on-premises MySQL server?

Accepted Answer

Enable binary logging with binlog_format = ROW. Native MySQL replication requires binary logging on the source server to capture all changes. Setting binlog_format = ROW ensures that row-level changes are logged, which is the recommended format for cross-version replication and is required by Amazon RDS for MySQL to support replication from an external source. Without binary logging enabled, the on-premises MySQL server cannot act as a replication master.

Answer

Enable the slow query log

Answer

Enable the audit log

Answer

Enable the error log

Question 11

Which TWO steps are required when migrating an Oracle database to Amazon RDS for Oracle using AWS DMS with ongoing replication? (Choose TWO.)

Accepted Answer

Enable archive logging on the source Oracle database.. Option C is correct because AWS DMS requires archive logging on the source Oracle database to capture ongoing changes for continuous replication. Archive logging ensures that redo logs are retained and available for DMS to read transaction changes after a log switch, enabling Change Data Capture (CDC) without data loss.

Answer

Run AWS Schema Conversion Tool (SCT) to convert the schema.

Answer

Enable minimal supplemental logging.

Answer

Create a VPC endpoint for the DMS replication instance.

Question 12

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.. Option A is correct because 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 13

Which TWO of the following are benefits of using Amazon RDS Proxy? (Choose TWO.)

Accepted Answer

Reduces the number of database connections by pooling them.. Amazon RDS Proxy acts as a connection broker between your application and the database, maintaining a pool of established connections. When the application opens a new connection, RDS Proxy reuses an idle connection from the pool, which reduces the total number of database connections and prevents the database from being overwhelmed. This pooling mechanism directly addresses the issue of connection exhaustion, especially in serverless or highly concurrent environments.

Answer

Automatically encrypts all traffic between the application and the database.

Answer

Provides built-in read/write splitting for read replicas.

Answer

Reduces storage costs by compressing data in transit.

Question 14

A company needs to store and manage user sessions for a web application. The application runs on multiple EC2 instances, and sessions must be accessible from any instance. The team wants a fully managed, highly available, and low-latency solution. Which AWS service should they use?

Accepted Answer

Amazon ElastiCache for Redis. Amazon ElastiCache for Redis is the correct choice because it provides a fully managed, in-memory data store with sub-millisecond latency, making it ideal for storing user session data that must be accessed from any EC2 instance. Redis supports atomic operations and data structures (e.g., TTL-based key expiration) that are well-suited for session management, and its replication and Multi-AZ failover ensure high availability. This meets the requirement for a fully managed, highly available, and low-latency solution without the overhead of managing a database cluster.

Answer

Amazon RDS for MySQL

Answer

Amazon DynamoDB

Answer

Amazon S3

Question 15

A company is deploying a new Amazon RDS for Oracle instance and needs to ensure high availability and automatic failover. Which TWO configurations should be used?

Accepted Answer

Multi-AZ deployment. Option B (Multi-AZ deployment) is correct because it provisions a synchronous standby replica in a different Availability Zone, enabling automatic failover without data loss when the primary instance fails. This meets the high availability and automatic failover requirements for Amazon RDS for Oracle.

Answer

Read Replicas in a different Region

Answer

Enhanced Monitoring

Answer

Deletion protection

Question 16

A company is deploying a multi-AZ Aurora MySQL database. They need to ensure that failover happens automatically with minimal data loss. Which configuration should be used?

Accepted Answer

Create an Aurora cluster with one primary and two readers in different Availability Zones.. Option C is correct because an Aurora cluster with one primary and two readers in different Availability Zones provides automatic failover with minimal data loss. Aurora uses a shared cluster volume that is replicated six ways across three AZs, ensuring that during a failover, the promoted reader has access to all committed transactions with no data loss. This configuration meets the requirement for multi-AZ high availability and automatic failover within a single region.

Answer

Deploy an Aurora Global Database with a primary in one region and a secondary in another region.

Answer

Use a Multi-AZ RDS for MySQL deployment.

Answer

Configure a single-AZ Aurora instance and enable cross-Region replication.

Question 17

A company is deploying a new web application that uses Amazon RDS for MySQL. To improve read performance, they add a read replica. However, the application reports stale data. What is the most likely cause?

Accepted Answer

The replication is asynchronous and there is replication lag.. Amazon RDS for MySQL uses asynchronous replication for read replicas. The primary instance commits writes and then sends the binary log (binlog) events to the replica, which applies them. This asynchronous nature introduces replication lag, meaning the replica may not have the most recent writes. If the application reads from the replica before the lag is resolved, it will see stale (older) data.

Answer

The application is using a connection pool that caches connections to the primary.

Answer

The read replica is in a different AWS Region.

Answer

The application is reading from the replica before the write is committed on the primary.

Question 18

A database team is migrating an on-premises Oracle database to Amazon Aurora PostgreSQL. The team needs to ensure minimal downtime and data consistency. Which approach should be used?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication using change data capture (CDC). AWS DMS with ongoing replication using change data capture (CDC) is the correct approach because it enables a live migration with minimal downtime. DMS can perform a full load of the Oracle database and then continuously replicate ongoing changes from Oracle to Aurora PostgreSQL, ensuring data consistency at the point of cutover. This method avoids the need for a long maintenance window and supports heterogeneous migrations with automatic schema conversion.

Answer

Use the PostgreSQL foreign data wrapper (FDW) to link the Oracle database

Answer

Use AWS Server Migration Service (SMS) to replicate the database

Answer

Use pg_dump and pg_restore to migrate the data during a maintenance window

Question 19

A company is using Amazon ElastiCache for Redis to cache database query results. The application team reports that cache hit ratio has dropped significantly. What is the first step to investigate?

Accepted Answer

Check the CacheHitRate and Evictions metrics in CloudWatch. When the cache hit ratio drops significantly, the first step is to investigate whether the cache is evicting keys due to memory pressure or if the working set no longer fits. CloudWatch metrics such as `CacheHitRate` and `Evictions` provide immediate visibility into these conditions without requiring direct Redis access. This aligns with the AWS Well-Architected Framework's principle of observability before making configuration changes.

Answer

Run the Redis INFO command to see memory usage

Answer

Review the ElastiCache event logs for node failures

Answer

Check the Redis AOF persistence logs

Question 20

An Amazon RDS for Oracle DB instance is experiencing high swap usage. The database administrator wants to reduce swap usage. Which action should be taken?

Accepted Answer

Increase the DB instance class to a larger size with more memory. High swap usage on an Amazon RDS for Oracle DB instance indicates that the operating system is using disk-based swap space as a substitute for physical RAM, which severely degrades database performance. Increasing the DB instance class to a larger size with more memory directly addresses the root cause by providing additional RAM, reducing or eliminating the need for swapping. This is the correct action because swap usage is a memory pressure issue, not a storage or availability problem.

Answer

Change the storage type from gp2 to io1

Answer

Delete archived redo logs to free up space

Answer

Enable Multi-AZ to distribute the load