DBS-C01 Workload-Specific Database Design Practice Test 28 — 15 Questions

Question 1

An IAM policy is attached to an application role that accesses a DynamoDB table named 'Orders'. The table has a global secondary index named 'OrderDateIndex'. The application needs to write new orders and query the index. Based on the exhibit, will the application be able to perform these operations?

Accepted Answer

Yes, the policy allows both writes and querying the index.. The policy allows PutItem on the table, so writes are allowed. For querying the index, the policy explicitly allows GetItem and Query on the index resource. However, the index resource ARN is correct. Therefore, both operations are allowed. Option B is wrong because the index is not denied; Option C is wrong because the policy includes the index; Option D is wrong because the policy covers both.

Answer

Yes, but only writes are allowed; index queries are denied.

Answer

No, the policy does not grant access to the index.

Answer

No, the policy denies Query on the index.

Question 2

A company runs an online auction platform on AWS. The application uses Amazon DynamoDB as the primary database, with a table 'Auctions' that has a partition key 'auction_id' (String) and sort key 'end_time' (Number). The table also has a global secondary index (GSI) on 'status' (String) and 'current_bid' (Number). The application frequently queries for active auctions sorted by current bid. Recently, the team noticed that queries on the GSI for active auctions with a high current_bid are returning results slowly. The DynamoDB table has 10,000 write capacity units (WCU) and 30,000 read capacity units (RCU) provisioned. The GSI has 5,000 RCU provisioned. The team suspects throttling on the GSI. What is the most likely cause of the slow queries?

Accepted Answer

The GSI's provisioned RCU is insufficient due to hot partitions.. Option C is correct because if the index key (status, current_bid) leads to hot partitions (e.g., many active auctions with similar current_bid), those partitions may be throttled even if overall provisioned RCU is not fully utilized. Option A is wrong because the table RCU is high, but index RCU is separate. Option B is wrong because there's no indication of WCU throttling for reads. Option D is wrong because the index key design is not necessarily wrong; hot partitions cause throttling.

Answer

The GSI key schema is inefficient for the query pattern.

Answer

The table's WCU is too low, causing throttling on writes that affects reads.

Answer

The table's RCU is too low for the application's read load.

Question 3

A company is running a MySQL database on Amazon RDS for a customer relationship management (CRM) application. The database has a table named 'contacts' with over 100 million rows. The application frequently runs queries to find contacts by email address. The email column has a B-tree index. Recently, the application started experiencing slow query performance. The team checked CloudWatch metrics and saw that the ReadIOPS for the RDS instance is consistently at 80% of the provisioned IOPS limit. The instance type is db.r5.large with 3000 provisioned IOPS (gp2). The buffer pool hit ratio is 95%. What is the most cost-effective design change to improve query performance?

Accepted Answer

Upgrade the RDS instance to db.r5.xlarge with 6000 provisioned IOPS.. Option B is correct because moving to a db.r5.xlarge with 6000 provisioned IOPS (gp2) doubles IOPS capacity, reducing IO wait. Option A is wrong because DynamoDB requires application changes. Option C is wrong because Elasticsearch is additional complexity and cost. Option D is wrong because the buffer pool hit ratio is already high; increasing memory won't help much.

Answer

Migrate the contacts table to Amazon DynamoDB with email as partition key.

Answer

Implement an Amazon OpenSearch Service cluster for email search.

Answer

Increase the buffer pool size by changing to a memory-optimized instance.

Question 4

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 5

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 6

A company wants to migrate their on-premises Oracle database to Amazon RDS for Oracle. They have a complex data loading process that uses Oracle Data Pump. Which migration approach is MOST efficient and minimizes downtime?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication from the source Oracle database.. AWS DMS can perform a one-time full load followed by ongoing replication using Oracle LogMiner or binary reader. This minimizes downtime because after the full load, DMS continuously applies changes from the source. Data Pump export/import requires downtime. SCT is used for schema conversion, not data movement. Backup and restore also requires downtime.

Answer

Use AWS Schema Conversion Tool (SCT) to convert the schema and then copy data files directly.

Answer

Take a physical backup of the on-premises database and restore to RDS.

Answer

Export data using Oracle Data Pump and import into RDS.

Question 7

A company runs a MongoDB-compatible workload on Amazon DocumentDB. They notice that many read requests are returning stale data even though reads are directed to the primary instance. What is the MOST likely cause?

Accepted Answer

The application is using a read preference that allows secondary reads.. DocumentDB uses a distributed storage volume with six copies across three Availability Zones. Reads from the primary are strongly consistent by default. However, if the application uses read preferences that allow secondary reads (e.g., 'secondaryPreferred'), then reads may go to replicas which are eventually consistent. The question implies reads are directed to primary, but if the application uses 'secondaryPreferred' and the primary is unavailable, reads may go to secondary. Alternatively, if the application uses a read preference that does not require primary, stale reads can occur. Option D addresses the most common cause: read preference set to allow secondary reads.

Answer

The application's session is pinned to a secondary replica despite requesting the primary.

Answer

The primary instance is experiencing high CPU utilization, causing delayed writes.

Answer

The storage volume is using the default eventually consistent configuration for primary reads.

Question 8

A company runs a critical PostgreSQL database on Amazon RDS Multi-AZ. They need to perform a major version upgrade (e.g., from 12 to 13) with minimal downtime. Which approach should they take?

Accepted Answer

Create a read replica of the DB instance, perform the major version upgrade on the replica, then promote the replica to a new primary and update the connection string.. RDS supports major version upgrades, but they require a brief downtime while the upgrade is applied. The recommended approach to minimize downtime is to create a read replica, upgrade the replica, promote it to a standalone instance, and then switch over. This way, the upgrade happens on the replica while the primary continues to serve traffic. Option A describes this correctly. Option B is the standard upgrade but incurs downtime. Option C is not supported (can't upgrade Multi-AZ without downtime). Option D suggests modifying the DB instance to Single-AZ, upgrading, then converting back to Multi-AZ, which also incurs downtime.

Answer

Take a snapshot, restore as a new instance with the upgraded engine version, and redirect traffic.

Answer

Initiate a major version upgrade directly on the Multi-AZ instance; the upgrade will be applied during the next maintenance window with minimal downtime.

Answer

Modify the DB instance to disable Multi-AZ, perform the upgrade, then re-enable Multi-AZ.

Question 9

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 10

A company runs a MySQL database on Amazon RDS. They need to export a subset of data to Amazon S3 for analysis using Amazon Athena. The data is stored in multiple tables with complex joins. What is the MOST efficient way to export the data?

Accepted Answer

Use the SELECT INTO OUTFILE S3 extension to export the query results directly to S3.. RDS for MySQL supports the SELECT INTO OUTFILE command to export query results to S3. This allows you to specify a SQL query (including joins) and export the results directly to S3 as CSV or other formats. This is efficient because it does not require an intermediate EC2 instance. Option A (mysqldump) exports table by table and requires manual processing. Option C (pg_dump) is for PostgreSQL. Option D (copy command) is for Redshift.

Answer

Use the COPY command from Amazon Redshift to pull data from RDS.

Answer

Use the AWS Schema Conversion Tool (SCT) to extract the data to S3.

Answer

Use mysqldump to export the tables and then upload the files to S3.

Question 11

A company recently migrated their PostgreSQL database to Amazon Aurora PostgreSQL. They notice that the average query latency has increased, especially for complex read queries. The DB instance size is adequate and CPU utilization is below 50%. What is the MOST likely cause of the increased latency?

Accepted Answer

The application is sending all read queries to the primary instance instead of offloading them to Aurora Replicas.. Aurora PostgreSQL uses a shared cluster volume, and by default, writes are sent to the primary instance. Read replicas (Aurora Replicas) can offload read traffic. If the application is not using read replicas for read queries, all queries hit the primary, which may become overloaded even if CPU is low due to other bottlenecks like memory or I/O. However, the most typical cause for increased read latency after migration to Aurora is the lack of read replicas or incorrect query optimization. Option D (Aurora Replicas not used) is the most likely. Option A (buffer cache) is possible but less likely with adequate memory. Option B (Auto Scaling) doesn't cause increased latency. Option C (parallel query) is a feature that can improve performance, not degrade it.

Answer

The Auto Scaling policy for the Aurora cluster is set to scale down too aggressively.

Answer

The Aurora cluster volume uses a smaller buffer cache than the original RDS instance.

Answer

The Aurora cluster is using the parallel query feature which adds overhead for complex queries.

Question 12

A startup is building a mobile app backend using Amazon DynamoDB. They anticipate unpredictable traffic spikes. Which DynamoDB feature should they use to handle the spikes without manual intervention?

Accepted Answer

Enable DynamoDB Auto Scaling for read and write capacity.. DynamoDB Auto Scaling adjusts provisioned throughput based on actual traffic, using CloudWatch alarms. This handles spikes automatically. On-Demand capacity mode is another option that handles spikes automatically but can be more expensive for predictable workloads. However, the question asks for a feature to handle unpredictable spikes. Auto Scaling is the traditional approach. On-Demand is also valid but the question may expect Auto Scaling as the classic answer. But to be precise, On-Demand is designed for unpredictable traffic. However, the options: A: Auto Scaling, B: DAX, C: Global Tables, D: TTL. Auto Scaling is the most direct answer.

Answer

Use DynamoDB Accelerator (DAX) as a cache layer.

Answer

Set up a TTL (Time to Live) to automatically expire old items.

Answer

Implement DynamoDB Global Tables for multi-region replication.

Question 13

A company runs a critical Oracle database on Amazon RDS. They need to implement a disaster recovery strategy that provides the lowest possible recovery point objective (RPO) and recovery time objective (RTO) across AWS Regions. Which TWO actions should they take? (Choose two.)

Accepted Answer

Configure cross-Region automated backups to copy backups to another Region.. To achieve cross-Region DR with low RPO/RTO, you can use an AWS DMS task with ongoing replication to an RDS instance in another Region. Additionally, you can enable Multi-AZ in the primary Region for high availability, but that doesn't provide cross-Region DR. Option C (cross-Region read replica) is not supported for Oracle. Option D (Cross-Region automated backups) is supported and provides RPO of a few minutes. Option E (Aurora Global Database) is for Aurora, not Oracle. The correct combination is: Option A (DMS) and Option D (Cross-Region backup restore). However, DMS provides continuous replication (low RPO) and Option D provides automated backups that can be restored in another Region (low RTO if restored). But Option A alone is not sufficient for RTO; you need a standby instance. The best answer is to use DMS for replication to a standby RDS instance in the secondary Region and use Cross-Region automated backups for additional protection. But the question asks for TWO actions. Option A + Option D is valid. Option B (Multi-AZ) is for HA within a Region. Option C is not supported. Option E is for Aurora. So A and D.

Answer

Enable Multi-AZ on the primary RDS instance.

Answer

Create a cross-Region read replica of the Oracle DB instance.

Answer

Use Amazon Aurora Global Database to replicate data across Regions.

Question 14

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 15

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.

DBS-C01 Workload-Specific Database Design Practice Test 28 — 15 Questions

Exhibit

DBS-C01 Workload-Specific Database Design Practice Test 28 — 15 Questions

Exhibit