DBS-C01 Practice Test 17 — 15 Questions

Question 1

A company runs an e-commerce application on Amazon RDS for MySQL. The application experiences read-heavy traffic during flash sales. The development team wants to offload read traffic without changing the application code. Which solution should be used?

Accepted Answer

Create an RDS Read Replica and point read traffic to the replica endpoint.. Option C is correct because Amazon RDS Read Replicas allow offloading read traffic from the primary DB instance without application changes. Option A is wrong because DynamoDB Accelerator (DAX) is for DynamoDB, not RDS. Option B is wrong because Multi-AZ is for high availability, not read scaling. Option D is wrong because ElastiCache requires application changes to use caching logic.

Answer

Implement an Amazon ElastiCache cluster and update the application to cache queries.

Answer

Configure Multi-AZ deployment for the RDS instance.

Answer

Use DynamoDB Accelerator (DAX) in front of the RDS instance.

Question 2

A company is designing a time-series database for IoT sensor data using Amazon DynamoDB. Each sensor sends a reading every second. The table uses 'sensor_id' as partition key and 'timestamp' as sort key. The application queries for the last hour of data for a specific sensor. The query uses 'KeyConditionExpression' with 'timestamp' between start and end time. The table has auto-scaling enabled. However, the query latency is high. What is the MOST likely cause?

Accepted Answer

The query is scanning from the beginning of time; use 'ScanIndexForward: false' and a 'Limit' parameter.. Option B is correct because the sort key 'timestamp' is in ascending order, so the most recent data is at the end of the sorted range. When querying for the last hour, DynamoDB may scan a large number of items before finding the recent ones, especially if the sensor has been running for a long time. Using 'ScanIndexForward: false' with a limit would reverse the order and retrieve recent items first. Option A is wrong because auto-scaling would add capacity if needed, but the issue is query design. Option C is wrong because the sort key is already 'timestamp'. Option D is wrong because DAX would reduce latency but not the underlying read consumption.

Answer

Enable DynamoDB Accelerator (DAX) to cache the query results.

Answer

The sort key should be 'sensor_id' and partition key should be 'timestamp'.

Answer

The table does not have enough read capacity units; increase the base capacity.

Question 3

A company uses Amazon DynamoDB to store session data for a web application. During peak hours, they experience occasional ProvisionedThroughputExceededException errors. The table has a read capacity of 1000 RCU and a write capacity of 500 WCU. The application uses strongly consistent reads. The traffic pattern shows short bursts of reads exceeding 1000 RCU. What is the MOST cost-effective way to handle these bursts without changing the application?

Answer

Enable DynamoDB Auto Scaling to adjust RCU dynamically

Answer

Increase RCU to 2000 and enable Auto Scaling

Answer

Switch to eventually consistent reads

Answer

Use DynamoDB Accelerator (DAX) for caching reads

Question 4

An e-commerce application stores order data in Amazon RDS for MySQL. The database has grown to 1.5 TB and the company needs to retain data for 7 years for compliance. Current queries are becoming slow due to the large table size. The compliance requirement mandates that data older than 1 year must be retained but is rarely accessed. What strategy would reduce the active table size while maintaining compliance?

Accepted Answer

Partition the table by date and archive partitions older than 1 year to Amazon S3 using AWS DMS.. Option C is correct because partitioning the table by date and archiving old partitions to a separate table or S3 meets compliance and reduces active table size. Option A is wrong because vertical partitioning (splitting columns) doesn't address the row count issue. Option B is wrong because read replicas do not reduce storage size. Option D is wrong because deleting data violates compliance.

Answer

Create a read replica and run reports against it.

Answer

Delete data older than 1 year and use automated backups for compliance.

Answer

Vertically partition the table to separate frequently and infrequently accessed columns.

Question 5

A financial services company uses Amazon RDS for MySQL with Multi-AZ and read replicas. The application suddenly reports increased write latency. The DB instance is a db.r5.large with 300 GB of General Purpose SSD (gp2) storage. CloudWatch metrics show Write IOPS is at 2,500 and Write Latency averages 50 ms. What is the most likely cause?

Accepted Answer

The gp2 volume has exhausted its I/O credit balance.. Option B is correct because gp2 volumes have a baseline of 3 IOPS per GB, so 300 GB provides 900 baseline IOPS, but can burst up to 3,000 IOPS using I/O credits. Sustained 2,500 IOPS may exhaust the credit balance, leading to throttling and increased latency. Option A is wrong because read replicas do not affect primary write latency. Option C is wrong because Multi-AZ synchronous replication adds minimal latency, typically 1-2 ms. Option D is wrong because 2,500 IOPS is below the burst maximum of 3,000 IOPS for gp2, so the issue is credit exhaustion, not hitting the maximum.

Answer

The read replica is under-provisioned causing replication lag.

Answer

The Write IOPS has exceeded the gp2 volume's maximum burst IOPS of 3,000.

Answer

Multi-AZ synchronous replication is causing high latency.

Question 6

A company uses Amazon DynamoDB to store user profiles. The access pattern is mostly GetItem by user_id. They want to reduce costs. Which design change is most effective?

Accepted Answer

Use DynamoDB Standard-IA table class for the user profiles table.. Option D is correct because DynamoDB Standard-IA is cheaper for data that is accessed less frequently. Option A is wrong because DAX adds cost. Option B is wrong because increasing read capacity increases cost. Option C is wrong because adding a GSI adds cost.

Answer

Increase the read capacity units to reduce throttling.

Answer

Add a Global Secondary Index on an additional attribute.

Answer

Add DynamoDB Accelerator (DAX) for caching.

Question 7

A company has a multi-player game that uses DynamoDB to store game state. The access pattern is write-heavy, and the game state for each active game session is updated frequently. The team notices throttling on the table during peak hours. The table has a partition key of game_id and no sort key. What design change would best reduce throttling?

Accepted Answer

Use a composite key with a random suffix on the partition key.. Option D is correct because using a write sharding pattern with a suffix distributes writes across partitions, avoiding hot spots. Option A is wrong because increasing read capacity does not help write throttling. Option B is wrong because DynamoDB Accelerator (DAX) only caches reads. Option C is wrong because global tables replicate data, not reduce throttling.

Answer

Enable DynamoDB global tables.

Answer

Enable DynamoDB Accelerator (DAX) for the table.

Answer

Increase the provisioned read capacity units (RCU).

Question 8

A company uses Amazon RDS for PostgreSQL to store sensor data. Each sensor sends a row every second. The table has grown to 500 GB and queries filtering on a timestamp column are slow even with an index. The team wants to improve query performance while keeping the data online. Which approach should they take?

Accepted Answer

Partition the table by time using PostgreSQL table partitioning. Partitioning the table by time (e.g., by day or month) allows PostgreSQL to prune partitions, reducing the amount of data scanned. This is a common pattern for time-series data. Adding more indexes can slow writes. Read replicas help with read scaling but not query performance on the primary. Changing to Aurora PostgreSQL with parallel query can help but partitioning is a more direct solution.

Answer

Migrate to Amazon Aurora PostgreSQL and enable parallel query

Answer

Add more indexes on the timestamp column

Answer

Create a read replica and direct queries to the replica

Question 9

A company is building a real-time analytics dashboard for IoT sensor data. The data arrives as JSON and needs to be stored in a way that supports fast ingestion and complex queries. Which database service is best suited?

Accepted Answer

Amazon Timestream. Amazon Timestream is a time-series database optimized for IoT data, with fast ingestion and built-in analytics functions. DynamoDB is not optimized for time-series queries. RDS is not designed for high-velocity time-series data. Redshift is for batch analytics.

Answer

Amazon RDS for PostgreSQL

Answer

Amazon DynamoDB with TTL

Answer

Amazon Redshift

Question 10

A company is designing a database for a social media application that stores user posts. Each post can have multiple tags. The workload requires low-latency queries to find all posts with a specific tag. Which database design is most suitable?

Accepted Answer

Amazon DynamoDB with a Global Secondary Index on the tag attribute.. Option A is correct because Amazon DynamoDB with a GSI on the tag attribute allows fast queries by tag. Option B is wrong because RDS for MySQL with a normalized schema would require joins, which are slower for this use case. Option C is wrong because ElastiCache is a cache, not a primary data store. Option D is wrong because Neptune is for graph data, not for this simple tag lookup.

Answer

Amazon ElastiCache for Memcached storing posts and tags as key-value pairs.

Answer

Amazon RDS for MySQL with a normalized schema and JOIN queries.

Answer

Amazon Neptune with a graph model for tags and posts.

Question 11

A company is migrating its on-premises MySQL database to Amazon Aurora MySQL. The current database has a table of 500 GB that is accessed by a nightly batch job that updates 80% of the rows. The company wants to minimize downtime during migration. Which migration strategy is MOST appropriate?

Accepted Answer

Use AWS Database Migration Service (DMS) with Aurora as the target.. Option B is correct because using AWS DMS with Aurora MySQL as the target allows a full load plus ongoing replication to minimize downtime. Option A is wrong because mysqldump would require application downtime during the dump and restore. Option C is wrong because an Aurora read replica can only be created from an existing Aurora instance, not from on-premises. Option D is wrong because S3 export/import is for data warehousing, not for minimal downtime migration.

Answer

Create an Aurora read replica from the on-premises database.

Answer

Export the data to Amazon S3 and load it into Aurora using the LOAD DATA FROM S3 command.

Answer

Use mysqldump to export the database and import it into Aurora.

Question 12

A company runs a MySQL database on Amazon RDS and wants to capture data changes to replicate to a separate reporting database. Which AWS service should be used to capture these changes with minimal impact on the source database?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication enabled.. Option D is correct because AWS DMS with ongoing replication (change data capture) captures changes from the source RDS MySQL binlog with minimal impact. Option A is wrong because RDS does not support native MySQL replication to external targets easily. Option B is wrong because DynamoDB Streams is for DynamoDB, not RDS. Option C is wrong because Kinesis Data Streams is not designed to directly capture RDS changes; requires additional configuration.

Answer

Use Amazon DynamoDB Streams to capture changes from the RDS instance.

Answer

Enable MySQL native replication from the RDS instance to the reporting database.

Answer

Use Amazon Kinesis Data Streams with a custom application to poll the binlog.

Question 13

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. Options A and D are correct. DynamoDB is a key-value and document database that provides single-digit millisecond latency at any scale. ElastiCache for Redis is an in-memory data store that can achieve sub-millisecond latency for key-value data. Option B (RDS) is relational and not designed for single-digit millisecond at millions of requests per second without heavy caching. Option C (Redshift) is a data warehouse. Option E (Neptune) is a graph database.

Answer

Amazon Neptune

Answer

Amazon Redshift

Answer

Amazon RDS for MySQL

Question 14

A company is migrating a 3 TB Oracle database to Amazon Aurora PostgreSQL. The database has a heavy OLTP workload with many small transactions. The migration must have minimal downtime. Which TWO strategies should the company use? (Choose two.)

Accepted Answer

Use AWS DMS with ongoing replication to capture and apply changes.. Options A and D are correct. AWS DMS with ongoing replication allows minimal downtime by replicating changes from Oracle to Aurora. Using Aurora PostgreSQL provides better compatibility with Oracle via the Babelfish feature? Actually, Babelfish is for SQL Server, not Oracle. But Aurora PostgreSQL supports many Oracle features. Option B is wrong because SCT helps assess but doesn't handle ongoing replication. Option C is wrong because converting to Aurora MySQL would require additional compatibility changes. Option E is wrong because a read replica cannot be created from Oracle.

Answer

Convert the database to Amazon Aurora MySQL instead.

Answer

Create an Aurora read replica from the Oracle database.

Answer

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

Question 15

An application is receiving the error shown in the exhibit. The application uses connection pooling. The RDS instance is a db.r5.large with max_connections set to 1000. What is the most likely cause?

Accepted Answer

The connection pool in the application is not releasing idle connections.. Option C is correct because connection pooling can accumulate connections if not properly configured, leading to exhaustion. Option A is wrong because 1000 is the default for db.r5.large. Option B is wrong because network ACLs affect connectivity, not the number of connections once established. Option D is wrong because the error indicates connections are being accepted but exhausted.

Answer

The security group is blocking incoming connections.

Answer

The max_connections parameter is set too low for the instance size.

Answer

The RDS instance is in a different VPC than the application.