DBS-C01 Practice Test 27 — 15 Questions

Question 1

A startup is building a social media application that needs to store user profiles, posts, comments, and likes. The data is highly interconnected, and the team wants to query relationships efficiently, such as 'find all friends of a user who liked a post'. Which database service is best suited for this workload?

Accepted Answer

Amazon Neptune. Amazon Neptune is a graph database designed for highly connected data, making it ideal for social graphs. Option A (DynamoDB) is wrong because it is a key-value/document database that requires additional application logic for graph queries. Option B (RDS) is wrong because relational databases can model graphs but are less efficient for deep relationship queries. Option D (ElastiCache) is wrong because it is a cache, not a primary database.

Answer

Amazon ElastiCache for Redis

Answer

Amazon DynamoDB

Answer

Amazon RDS for PostgreSQL

Question 2

A company is designing a database for an IoT application that receives millions of sensor readings per second. Each reading is a small JSON payload (timestamp, device_id, metric, value). The primary query pattern retrieves the most recent reading for a given device. Which AWS database service is BEST suited for this workload?

Accepted Answer

Amazon DynamoDB. DynamoDB is a key-value and document database optimized for high-velocity writes and low-latency point lookups. With a primary key of device_id and a sort key of timestamp, the query for the most recent reading can use ScanIndexForward: false and limit 1, which is efficient. RDS and Aurora are relational and not ideal for high-throughput writes. ElastiCache is a cache, not a durable database. Redshift is for analytics.

Answer

Amazon Aurora

Answer

Amazon ElastiCache for Redis

Answer

Amazon RDS for MySQL

Question 3

A company is designing a database for a global e-commerce platform that requires low-latency reads and writes from multiple AWS Regions. The database must support ACID transactions and complex queries with joins. Which TWO services should they consider? (Choose two.)

Accepted Answer

Amazon DynamoDB with Global Tables. For global low-latency with ACID transactions and complex queries, Amazon Aurora (especially with Global Database) is a strong choice. DynamoDB is not relational and does not support complex joins natively. RDS Multi-AZ is single-region. ElastiCache is not a database. Redshift is for analytics. The correct answers are Aurora (which supports Global Database for multi-region) and possibly RDS with cross-Region replication, but RDS does not have native global database capability like Aurora. However, the question says 'which TWO services', and the best two are Aurora and DynamoDB? But DynamoDB does not support complex joins. Option A (DynamoDB) is often used for global scale but lacks joins. Option B (Aurora) is the best fit. Option C (RDS) can be used with cross-Region read replicas but not for writes. Option D (ElastiCache) is cache. Option E (Redshift) is for analytics. The only viable services for ACID and joins are Aurora and possibly RDS if they accept eventual consistency? But the question says 'low-latency reads and writes' and 'global', so Aurora Global Database is the best. The second could be DynamoDB if they use serverless and global tables, but the question explicitly says 'complex queries with joins', which DynamoDB does not support. Therefore, the correct pair is likely Aurora and something else? Actually, there is no other service that fully meets all requirements. Perhaps the answer is Aurora and RDS? But RDS does not support multi-region writes. The most reasonable is to select Aurora and DynamoDB for different workloads, but the stem implies a single database. Given the constraints, the best two are Aurora (for relational) and DynamoDB (for non-relational), but they are different paradigms. However, the exam may expect Aurora and DynamoDB as two services for different parts of the application. Alternatively, the correct answer might be Aurora and RDS with cross-Region replication? But RDS does not have global tables. I'll go with Aurora and DynamoDB as the two services that can be used together to meet the requirements: DynamoDB for high-speed key-value access and Aurora for complex queries. The question says 'which TWO services should they consider', implying they may use both. So I'll choose A and B.

Answer

Amazon ElastiCache for Redis with global datastore

Answer

Amazon RDS for MySQL with cross-Region read replicas

Answer

Amazon Redshift with cross-Region snapshots

Question 4

A gaming company uses Amazon DynamoDB to store player scores. The table has a partition key of 'game_id' and a sort key of 'player_id'. They notice that during peak hours, write requests for a popular game 'g123' are throttled, while other games are unaffected. What is the most likely cause and solution?

Accepted Answer

Use a composite partition key with a random suffix to distribute writes.. Option D is correct because the partition key 'game_id' causes a hot partition for game 'g123'. Using a write shard pattern distributes writes across multiple partitions. Option A (increase WCUs) may not help if the partition is hot. Option B (DAX) is for reads, not writes. Option C (auto-scaling) won't solve hot partition issue.

Answer

Enable DynamoDB Accelerator (DAX) to cache writes.

Answer

The write capacity is too low; increase the table's write capacity units.

Answer

Enable auto-scaling on the table to handle burst write traffic.

Question 5

Which THREE factors should be considered when selecting a database for a time-series workload (e.g., IoT sensor data) that requires high write throughput and efficient data retention?

Accepted Answer

Configure automatic data expiration using TTL (Time-to-Live).. Options A, C, and D are correct. Amazon Timestream is purpose-built for time-series data and supports data retention policies. Partitioning by time in a relational database can improve query performance. Configuring automatic data expiration using TTL is essential for managing data lifecycle. Option B (normalization) is not typically beneficial for time-series workloads as it can degrade write performance. Option E (using Amazon RDS Proxy) is for connection pooling, not specific to time-series.

Answer

Normalize the schema to reduce data duplication.

Answer

Use Amazon RDS Proxy to manage database connections.

Question 6

A company is moving a large-scale time-series application from Cassandra to a managed AWS service. The workload involves high-frequency writes (millions per second) and queries that aggregate data over time windows. Which THREE AWS services are suitable for this time-series workload?

Accepted Answer

Amazon OpenSearch Service. Amazon Timestream is purpose-built for time-series data. Amazon DynamoDB with time-series partitioning (using partition key as entity ID and sort key as timestamp) can handle high-volume writes and support time-based queries. Amazon OpenSearch Service can ingest time-series data and provide aggregation queries. Option D (Redshift) is wrong because it is optimized for OLAP on structured data, not high-frequency writes. Option E (Aurora) is wrong because it is not designed for time-series ingestion at millions of writes per second.

Answer

Amazon Aurora

Answer

Amazon Redshift

Question 7

A web application uses Amazon DynamoDB as its database. The application frequently queries items using a secondary index. The index's partition key has high cardinality, but the query latency is higher than expected. Which action would MOST likely improve query performance?

Accepted Answer

Increase the read capacity units (RCU) for the global secondary index.. DynamoDB secondary indexes have their own provisioned throughput. If the index's read capacity is insufficient, queries will be throttled or have higher latency. Increasing the read capacity for the index directly addresses this. Option A (adding more sort keys) doesn't apply to queries on a secondary index. Option C (changing to global secondary index) is not needed if it's already a GSI. Option D (switching to scan) is less efficient.

Answer

Use a Scan operation instead of Query to retrieve items from the index.

Answer

Add additional sort key attributes to the index to better distribute the data.

Answer

Convert the global secondary index to a local secondary index.

Question 8

A company is migrating a large Oracle database to Amazon Aurora PostgreSQL. They need to minimize downtime and validate data consistency after migration. Which THREE steps should they include in their migration plan? (Choose THREE.)

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication to keep the target in sync.. Option A (AWS DMS with ongoing replication) minimizes downtime. Option B (Schema Conversion Tool) helps convert Oracle schema to PostgreSQL. Option D (data validation) ensures consistency. Option C (homogeneous migration) is not needed; DMS works. Option E (Aurora Replicas) is for read scaling, not migration.

Answer

Create multiple Aurora Replicas for read scaling during migration.

Answer

Perform a homogeneous migration directly from Oracle to Aurora.

Question 9

Refer to the exhibit. A DynamoDB table has a primary key of pk (partition key) and sk (sort key). An application needs to perform GetItem and Query operations but should only be allowed to retrieve the pk and sk attributes. The IAM policy above is applied to the application's IAM role. Why does the policy fail to achieve the goal?

Accepted Answer

The Deny statement does not prevent retrieval of all attributes when no ProjectionExpression is specified.. The Deny statement with the condition ForAllValues:StringNotEquals will deny a request if ANY requested attribute is not in the specified list. However, GetItem and Query can request specific attributes using ProjectionExpression. If the request does not specify any attributes, the condition evaluates to true (since no values to compare), and the Deny does not apply, allowing full item retrieval. Also, the condition uses StringNotEquals incorrectly; it should use StringEquals. The correct approach is to use a condition on dynamodb:Select or use a fine-grained access control with a condition on the requested attributes.

Answer

The Deny statement uses the wrong condition key; it should use 'dynamodb:Select' instead of 'dynamodb:Attributes'.

Answer

The policy should use 'dynamodb:ReturnValues' condition key.

Answer

The Allow statement should include 'dynamodb:Scan' to allow Query operations.

Question 10

A company is running a PostgreSQL database on Amazon RDS. They need to improve read performance for a reporting application that runs complex queries. The reporting application can tolerate slightly stale data. Which THREE actions should they take? (Choose three.)

Accepted Answer

Modify the DB parameter group to optimize settings for reporting workloads, such as increasing shared_buffers and work_mem.. To improve read performance, you can create read replicas to offload queries, adjust instance class for more CPU/memory, and use parameter groups to optimize for reporting workloads (e.g., increased shared_buffers, work_mem). Option A (Multi-AZ) improves availability, not read performance. Option B (read replicas) distributes read traffic. Option C (ElastiCache) can cache results of frequent queries. Option D (instance class) provides more resources. Option E (parameter groups) allows tuning. So the correct three are B, D, and E. Option C is also valid but not typically 'action' on RDS; it's an additional service. The question says 'actions they should take' which could include using ElastiCache. However, the exam often considers creating read replicas, modifying instance class, and optimizing parameters as direct actions. I'll choose B, D, E.

Answer

Enable Multi-AZ on the RDS instance.

Answer

Implement an Amazon ElastiCache cluster to cache query results.

Question 11

A company needs to store and analyze log data from thousands of servers. The logs are timestamped and rarely updated. Queries are mostly time-range aggregations. Which database service is best suited for this workload?

Accepted Answer

Amazon CloudWatch Logs. Option B is correct because Amazon CloudWatch Logs is a managed service for log storage and analysis. Option A (RDS) is not optimized for log data. Option C (DynamoDB) is not designed for log aggregation queries. Option D (ElastiCache) is an in-memory cache, not persistent log storage.

Answer

Amazon ElastiCache for Redis

Answer

Amazon DynamoDB

Answer

Amazon RDS for PostgreSQL

Question 12

Which TWO design patterns help meet ACID compliance requirements in a distributed database environment while maintaining high availability?

Accepted Answer

Implement Amazon Aurora Global Database for cross-Region ACID transactions.. Options B and D are correct. Amazon Aurora Global Database allows cross-region replication with ACID compliance within each region. Using DynamoDB Transactions provides ACID guarantees across multiple items within a single AWS account and region. Option A (eventual consistency) is not ACID. Option C (saga pattern) is for eventual consistency in microservices. Option E (DynamoDB Streams) enable change data capture but not ACID.

Answer

Use an eventually consistent read model to improve performance.

Answer

Adopt a saga pattern to manage distributed transactions.

Answer

Implement DynamoDB Streams to capture changes for audit.

Question 13

A financial services company uses Amazon DynamoDB to store transaction records. The table has a partition key of 'account_id' and a sort key of 'transaction_time'. Recent queries for a specific account's transactions within a time range are experiencing high latency. The table has read capacity units set to auto-scaling. Which design change would most improve query performance?

Accepted Answer

Create a global secondary index with a different partition key.. Option B is correct because using a secondary index with a different partition key can avoid hot partitions caused by frequent access to the same account. Option A (increasing RCUs) may not help if the partition is hot. Option C (changing sort key) won't help if the partition is overloaded. Option D (DAX) caches results but doesn't fix the underlying hot partition issue.

Answer

Change the sort key to a composite attribute for better filtering.

Answer

Enable DynamoDB Accelerator (DAX) for the table.

Answer

Increase the read capacity units for the table.

Question 14

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The database has a large table with a BLOB column storing PDF files. Which migration approach minimizes downtime?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication.. Option B is correct because AWS DMS can perform ongoing replication to keep the target in sync during the full load, minimizing downtime. Option A is wrong because exporting and importing BLOBs can be time-consuming and cause significant downtime. Option C is wrong because direct backup restore requires a compatible format and may not support ongoing replication. Option D is wrong because disabling BLOB columns during migration is not practical for the application.

Answer

Use Oracle Data Pump to export the table and import into RDS.

Answer

Use Oracle RMAN to back up the database and restore to RDS.

Answer

Export the table without the BLOB column, then import the BLOBs separately.

Question 15

A company wants to migrate a 2 TB PostgreSQL database from on-premises to Amazon Aurora PostgreSQL. The database has high write throughput and the migration must have minimal impact on source performance. Which solution is MOST appropriate?

Accepted Answer

Use pglogical to set up logical replication from the source to Aurora.. Option C is correct because using pglogical for logical replication allows near real-time replication with minimal overhead on the source. Option A is wrong because AWS DMS with ongoing replication can add some overhead to the source due to continuous fetching of changes. Option B is wrong because native PostgreSQL streaming replication requires the source to be a primary server and may cause performance impact. Option D is wrong because using a read replica reduces performance impact but requires a replica already set up.

Answer

Create a read replica of the on-premises database and promote it to Aurora.

Answer

Use AWS DMS with ongoing replication from the source to Aurora.

Answer

Set up native PostgreSQL streaming replication from on-premises to Aurora.