DBS-C01 Workload-Specific Database Design Practice Test 18 — 15 Questions

Question 1

A company is building a real-time leaderboard for a mobile game using Amazon DynamoDB. The leaderboard displays the top 100 players by score. The table has 'game_id' as partition key and 'player_id' as sort key. The score is updated frequently. Which THREE design patterns should the company implement to ensure low-latency reads for the leaderboard? (Choose three.)

Accepted Answer

Enable DynamoDB Accelerator (DAX) to cache the leaderboard query.. Option B is correct because DynamoDB Accelerator (DAX) provides an in-memory cache that can serve repeated leaderboard queries with microsecond latency, reducing the read load on the base table and avoiding throttling. For a real-time leaderboard that is read frequently, DAX ensures low-latency responses without needing to query DynamoDB directly each time.

Answer

Use 'ScanIndexForward: false' on the base table to get top players.

Answer

Use 'begins_with' operator on the sort key to filter by score range.

Question 2

A gaming company runs a global leaderboard on Amazon DynamoDB. The leaderboard is updated frequently and must return the top 100 scores in milliseconds. The current design uses a single table with a Global Secondary Index (GSI) on score. However, the query to retrieve top scores often throttles under load. Which design change would best improve performance?

Accepted Answer

Implement a write shard pattern using a random suffix on the partition key and a GSI on score.. Option B is correct because the write shard pattern distributes high-frequency writes across multiple partition keys by appending a random suffix, preventing hot partitions. The GSI on score still allows efficient top-N queries by scanning the index in descending order. This avoids throttling by spreading write capacity evenly, while the GSI remains a sparse index that can be queried without impacting the base table's write throughput.

Answer

Use a scan operation with a filter to retrieve top scores.

Answer

Add DynamoDB Accelerator (DAX) in front of the table.

Answer

Switch to strongly consistent reads for the leaderboard query.

Question 3

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 4

A startup is building a social media application with a news feed feature. The feed must be personalized and updated in real-time as users post. Which AWS database service is best suited for this workload?

Accepted Answer

Amazon ElastiCache for Redis with sorted sets and pub/sub. Option C is correct because Amazon ElastiCache for Redis supports sorted sets and pub/sub, ideal for real-time feeds. Option A is wrong because DynamoDB is optimized for key-value access, not for real-time feed aggregation across many users. Option B is wrong because RDS is not designed for sub-millisecond real-time updates. Option D is wrong because S3 is object storage, not a database for real-time queries.

Answer

Amazon DynamoDB with Global Secondary Indexes

Answer

Amazon S3 with Select and Glacier

Answer

Amazon RDS for PostgreSQL with read replicas

Question 5

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 6

A company runs an e-commerce platform on Amazon Aurora MySQL. The platform experiences high traffic during flash sales. To handle the load, they want to offload read traffic to read replicas. However, they are concerned about replication lag causing stale data for inventory checks. Which three strategies can reduce replication lag? (Choose three.)

Accepted Answer

Enable binary log replication with parallel apply on replicas.. Option A (Use Aurora Auto Scaling) is correct because it adds replicas to distribute load. Option B (Use Binary Log Replication with parallel apply) is correct because it improves replication throughput. Option D (Use lower isolation levels on replicas) is correct because it reduces locking and improves apply speed. Option C is wrong because increasing instance size of replicas helps, but not of the writer; the bottleneck is replica apply. Option E is wrong because synchronous replication would impact write performance.

Answer

Implement synchronous replication between writer and replicas.

Answer

Increase the instance size of the writer instance.

Question 7

A company wants to store session state for a web application that runs on Amazon EC2 instances behind an Application Load Balancer. The session data is ephemeral and must be highly available. Which two AWS services are suitable for this use case? (Choose two.)

Accepted Answer

Amazon DynamoDB. Option A (ElastiCache for Redis) is correct because it provides low-latency in-memory storage with replication for HA. Option C (DynamoDB) is correct because it is a highly available, fast key-value store. Option B is wrong because RDS is relational and not optimized for session state. Option D is wrong because S3 is not low-latency. Option E is wrong because Redshift is a data warehouse.

Answer

Amazon Redshift

Answer

Amazon S3

Answer

Amazon RDS for MySQL

Question 8

An application using the above IAM policy is trying to perform a Scan operation on the 'Orders' table. What will happen?

Accepted Answer

The Scan operation will fail because the explicit Deny on dynamodb:Scan overrides the Allow.. Option D is correct because the explicit Deny for dynamodb:Scan overrides any Allow. Option A is wrong because the Deny is explicit and not ambiguous. Option B is wrong because the policy explicitly denies Scan. Option C is wrong because the policy does not allow Scan; the explicit Deny applies.

Answer

The Scan operation will succeed because the Deny is on all resources but the Allow is specific to the table.

Answer

The Scan operation will succeed because the policy allows other operations on the table.

Answer

The Scan operation will fail because the policy does not explicitly allow Scan.

Question 9

A developer is designing a DynamoDB table for an order management system using the above CloudFormation template. The application needs to query orders by CustomerID. The current design has a GSI on CustomerID. However, the developer notices that the GSI has low write throughput and often throttles. What is the most cost-effective way to improve write throughput on the GSI?

Accepted Answer

Increase the WriteCapacityUnits of the GSI from 5 to a higher value.. Option A is correct because increasing the GSI's write capacity directly addresses the throttling. Option B is wrong because increasing table write capacity does not affect GSI capacity; GSI has its own. Option C is wrong because changing projection to KEYS_ONLY reduces storage but not write throughput. Option D is wrong because SQS does not help with DynamoDB write throughput.

Answer

Change the ProjectionType of the GSI to KEYS_ONLY.

Answer

Use Amazon SQS to buffer writes to the table.

Answer

Increase the WriteCapacityUnits of the table.

Question 10

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.

Question 11

A company needs to store time-series data from IoT sensors. Each sensor sends a reading every minute. The data is rarely accessed after 30 days. The query pattern is to retrieve all readings for a specific sensor within a time range. Which AWS database is most cost-effective?

Accepted Answer

Amazon Timestream. Option B is correct because Timestream is purpose-built for time-series data with automatic tiering. Option A is wrong because DynamoDB is more expensive for this pattern. Option C is wrong because RDS is not optimized for time-series. Option D is wrong because Redshift is for analytics, not real-time ingestion.

Answer

Amazon Redshift

Answer

Amazon DynamoDB with Time-to-Live (TTL)

Answer

Amazon RDS for PostgreSQL with partitioning

Question 12

A company runs a global application using Amazon Aurora Global Database. The primary region is us-east-1, and secondary regions are eu-west-1 and ap-southeast-1. The application reports that writes to the primary are taking longer than expected. What is the most likely cause?

Accepted Answer

The Global Database replication to secondary regions is causing synchronous commit latencies.. Aurora Global Database uses asynchronous replication from the primary to secondary regions, not synchronous. However, the question states writes to the primary are taking longer than expected, which is a symptom of synchronous replication overhead. In Aurora Global Database, the primary commits locally and then asynchronously replicates to secondaries, so writes should not be directly impacted by secondary region latency. The most likely cause is that the primary DB instance is under-provisioned (Option C), leading to resource contention and slower write operations.

Answer

Multi-AZ failover occurred in the primary region.

Answer

The primary DB instance is under-provisioned.

Answer

Read replicas in secondary regions are overloaded.

Question 13

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 14

A company needs to store and query graph data (nodes and edges) for a social network. They require low-latency traversals. Which AWS database is best suited?

Accepted Answer

Amazon Neptune. Option B is correct because Neptune is a purpose-built graph database. Option A is wrong because RDS is relational. Option C is wrong because DynamoDB is key-value. Option D is wrong because ElastiCache is in-memory cache, not a graph database.

Answer

Amazon RDS for MySQL

Answer

Amazon ElastiCache for Redis

Answer

Amazon DynamoDB

Question 15

A data analyst reports that a nightly ETL job to Amazon Redshift is failing with timeout errors shown in the exhibit. The cluster is a dc2.large with 2 nodes. The ETL job inserts large volumes of data. What is the most likely cause?

Accepted Answer

The cluster has insufficient disk space for the data load.. Option C is correct because dc2 nodes have limited local SSD storage; if the cluster runs out of disk space, writes time out. Option A is wrong because Redshift does not have a max_connections parameter like RDS. Option B is wrong because network ACLs would cause connection failures, not timeouts after connection. Option D is wrong because WLM queue timeouts cause different errors.

Answer

The cluster has reached the maximum number of connections.

Answer

The workload manager (WLM) queue timeout is too low.

Answer

The security group is blocking inbound traffic from the ETL server.