DBS-C01 Practice Exam 53 — 20 Questions

Question 1

A startup uses Amazon ElastiCache for Redis as a caching layer for its database. Users report that application responses are slow. The developer checks the ElastiCache metrics and sees that 'CacheHits' are low and 'CacheMisses' are high. What is the most likely cause?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The cache key TTL is too short, causing frequent evictions.. A low cache hit ratio and high cache miss ratio indicate that the cache is not storing data that is frequently requested. The most likely cause is that the Time-To-Live (TTL) for cache keys is set too short, causing data to be evicted before it can be reused. Option A is incorrect because read replicas improve read scalability but do not directly affect cache hit ratio. Option B is incorrect because write capacity is not relevant for a caching layer that primarily serves reads. Option C is incorrect: while high CPU utilization can cause latency, it would not specifically cause low cache hits and high misses.

Answer

The cluster does not have enough read replicas.

Answer

The ElastiCache cluster does not have enough write capacity.

Answer

The ElastiCache nodes have high CPU utilization.

Question 2

An e-learning platform uses Amazon Aurora MySQL for its database. The application runs reporting queries that scan large portions of the database, causing high CPU utilization on the primary instance. The primary instance is a db.r5.2xlarge with 64 GB memory. The reporting queries are not time-sensitive but need to return results within 5 minutes. The operations team wants to reduce the impact on the primary instance without increasing costs significantly. Which action should be taken?

Accepted Answer

Create an Aurora Replica and configure the reporting application to connect to the replica endpoint. To create an Aurora Replica and direct reporting traffic to it. This offloads the heavy reporting queries from the primary instance, reducing CPU impact without significant cost increase. Aurora Replicas share the same storage and are cost-effective for read-heavy workloads.

Answer

Modify the DB cluster parameter group to enable result set caching

Answer

Use Amazon ElastiCache to cache the reporting results

Answer

Increase the primary instance to db.r5.4xlarge

Question 3

A developer is troubleshooting an issue where an IAM user cannot perform a 'DescribeTable' action on a DynamoDB table. The IAM policy attached to the user is: {"Version":"2012-10-17","Statement":[{"Effect":"Allow","Action":["dynamodb:GetItem","dynamodb:PutItem"],"Resource":"*"}]}. What is the most likely reason for the failure?

Accepted Answer

The policy does not include the 'dynamodb:DescribeTable' action.. The IAM policy explicitly allows only dynamodb:GetItem and dynamodb:PutItem. Because IAM policies are deny-by-default, any action not explicitly allowed is implicitly denied. Since dynamodb:DescribeTable is not listed in the Action array, the user cannot perform it, regardless of the Resource being '*'. This is the most likely and direct cause of the failure.

Answer

The policy uses lowercase 'dynamodb' but the action is case-sensitive.

Answer

There is an implicit Deny for DescribeTable due to a service control policy.

Answer

The resource specified in the policy is '*' which does not include the table.

Question 4

A company is deploying a new web application on Amazon RDS for MySQL and expects read-heavy traffic. The database must be highly available. Which deployment approach meets these requirements?

Accepted Answer

Deploy a Multi-AZ instance and create read replicas.. Deploying a Multi-AZ RDS for MySQL instance provides automatic failover for high availability, while adding read replicas offloads read-heavy traffic from the primary instance, improving read scalability. Read replicas can be placed in different Availability Zones to further enhance resilience and read performance.

Answer

Deploy a Multi-AZ instance without read replicas.

Answer

Deploy a Single-AZ instance with a Multi-AZ read replica.

Answer

Deploy a Single-AZ instance and use ElastiCache for caching.

Question 5

Which THREE factors should be considered when choosing between Amazon RDS and Amazon DynamoDB for a new application? (Choose THREE.)

Accepted Answer

The query patterns and access methods required by the application.. Option C is correct because RDS is a relational engine queried with SQL joins and ad-hoc queries, while DynamoDB is a NoSQL key-value/document store accessed by primary key or secondary indexes, so the application's query patterns and access methods directly determine which service fits. Option D is correct because complex multi-table transactions and joins are natively supported by RDS engines (e.g., PostgreSQL, MySQL, Oracle, SQL Server) via SQL and ACID transactions, whereas DynamoDB offers only single-item or TransactWriteItems transactions without joins. Option E is correct because DynamoDB provides seamless horizontal scaling with virtually unlimited throughput via partition keys and provisioned/on-demand capacity, while RDS scales primarily vertically and requires read replicas or sharding, so expected scalability and throughput drive the choice. Option A is not a deciding factor because both RDS and DynamoDB support encryption at rest (RDS via KMS-backed storage encryption, DynamoDB via AWS-owned or customer-managed KMS keys). Option B is also not a deciding factor because both services offer Multi-AZ high availability — RDS through Multi-AZ standby deployments and DynamoDB through its built-in multi-AZ replication across three Availability Zones.

Answer

The requirement for encryption at rest.

Answer

The need for multi-AZ high availability.

Question 6

A company is designing a database for an e-commerce platform that requires ACID transactions for order processing, complex joins for inventory reporting, and the ability to scale read replicas across multiple AWS regions. Which database service best meets these requirements?

Accepted Answer

Amazon Aurora. Amazon Aurora is the correct choice because it provides full ACID compliance for transactional workloads, supports complex joins via its MySQL/PostgreSQL-compatible relational engine, and offers up to 15 low-latency read replicas that can be placed in multiple AWS Regions using Aurora Global Database. This combination of strong consistency, relational query capabilities, and cross-region read scaling directly matches the e-commerce platform's requirements.

Answer

Amazon DynamoDB

Answer

Amazon RDS for SQL Server

Answer

Amazon Redshift

Question 7

A company wants to migrate its on-premises Oracle database to Amazon Aurora PostgreSQL. The company needs to automatically convert the Oracle schema to PostgreSQL-compatible format. Which AWS service should the company use?

Accepted Answer

AWS Schema Conversion Tool (AWS SCT). AWS Schema Conversion Tool (AWS SCT) is designed specifically to convert database schemas from one engine to another, including Oracle to Amazon Aurora PostgreSQL. It automatically translates Oracle DDL (tables, indexes, stored procedures, functions, etc.) into PostgreSQL-compatible format, handling data type mappings, PL/SQL to PL/pgSQL conversion, and other schema-level transformations. AWS DMS handles data migration, not schema conversion, making SCT the correct choice for this requirement.

Answer

AWS Database Migration Service (AWS DMS) with the Oracle native dump and load option

Answer

AWS Server Migration Service (AWS SMS)

Answer

AWS Database Migration Service (AWS DMS)

Question 8

Which TWO options are valid methods to migrate an on-premises Microsoft SQL Server database to Amazon RDS for SQL Server with minimal downtime? (Choose 2.)

Accepted Answer

Use AWS DMS with ongoing replication. Option C is correct because AWS Database Migration Service (AWS DMS) can perform a full load plus change data capture (CDC) ongoing replication from an on-premises SQL Server to Amazon RDS for SQL Server, allowing you to cut over with minimal downtime. Option D is correct because RDS for SQL Server supports native backup and restore: you take a native .bak backup, upload it to Amazon S3, and restore it to the RDS instance using the rds_backup_database stored procedure, which is a supported migration path (though it is typically a one-time restore rather than continuous replication). Option A is not appropriate because AWS Snowball Edge is a physical data-transfer device for bulk data movement, not a live database migration mechanism with cutover control. Option B is not a migration method for this scenario because SSIS is an ETL tool for transforming and moving data, not a service designed to replicate an entire SQL Server database with minimal downtime. Option E is not correct because AWS Direct Connect is only a dedicated network connection that can reduce latency and improve transfer reliability, but it does not itself perform the database migration or replication.

Answer

Use AWS Snowball Edge

Answer

Use SQL Server Integration Services (SSIS)

Answer

Use AWS Direct Connect

Question 9

A company is migrating a 5 TB Oracle database to Amazon RDS for Oracle. The database has several large tables with LOB columns. The migration must have minimal downtime. Which approach should be taken?

Accepted Answer

Use AWS DMS with LOB support and ongoing replication from Oracle to RDS.. AWS DMS with LOB support and ongoing replication (change data capture, CDC) is the correct approach because it enables a near-zero downtime migration by continuously replicating changes from the source Oracle database to Amazon RDS for Oracle after an initial full load. DMS handles large LOB columns efficiently using its 'Full LOB mode' or 'Limited LOB mode' settings, which are critical for tables with LOB data. The combination of full load + CDC ensures minimal downtime, as the target remains synchronized until cutover.

Answer

Use Oracle GoldenGate to replicate data to RDS.

Answer

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

Answer

Copy the database files to Amazon S3 and use the rdsadmin.rds_restore_from_s3 procedure.

Question 10

A company is migrating an on-premises MySQL database to Amazon RDS for MySQL. The database is 2 TB in size and the network bandwidth is 100 Mbps. The company needs to minimize downtime. Which migration strategy should be used?

Accepted Answer

Use AWS Database Migration Service (DMS) with ongoing replication.. AWS DMS with ongoing replication is the correct strategy because it allows you to perform a full load of the 2 TB database while simultaneously capturing ongoing changes from the source MySQL binlog. This minimizes downtime by enabling a cutover with only a brief pause to ensure replication lag is zero, rather than requiring a long period of application downtime for a full export and import.

Answer

Copy database files to Amazon S3, then restore to RDS using native restore.

Answer

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

Answer

Use AWS Server Migration Service to migrate the database server.

Question 11

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The database experiences a failover event, and after failover, the application reports increased latency. Which action should the database specialist take to diagnose the issue?

Accepted Answer

Check Amazon CloudWatch metrics for Database Connections and Latency, and verify DNS resolution.. After a Multi-AZ failover, the DNS record for the RDS endpoint is updated to point to the new primary in a different Availability Zone. If the application's DNS cache still resolves to the old IP (which is now unreachable or in a different AZ), connections may time out or route suboptimally, increasing latency. Checking CloudWatch metrics for Database Connections and Latency helps isolate whether the issue is due to connection churn, resource contention, or DNS caching, while verifying DNS resolution confirms the application is connecting to the correct endpoint.

Answer

Promote the secondary instance to primary manually.

Answer

Create a new read replica and redirect traffic.

Answer

Force a reboot of the DB instance to reset connections.

Question 12

A company is using Amazon Redshift for data warehousing. The VACUUM operation is taking longer than expected, and the database administrator wants to identify the tables that require the most vacuuming effort. Which system table should be queried to find the percentage of deleted rows per table?

Accepted Answer

SVV_TABLE_INFO. (SVV_TABLE_INFO) is correct because this system table contains tombstone and unsorted statistics, including the percentage of deleted rows per table, which helps identify tables requiring vacuuming. Option A (STL_QUERY) is incorrect because it stores query execution logs, not table statistics. Option B (STV_TBL_PERM) is incorrect as it provides information about permanent table block allocations but not deleted row ratios. Option C (PG_TABLE_DEF) is incorrect because it holds table schema definitions only, not operational metrics.

Answer

STL_QUERY

Answer

STV_TBL_PERM

Answer

PG_TABLE_DEF

Question 13

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.. Option C is correct because RDS read replicas offload read-only reporting queries from the primary instance, and since the reporting application tolerates slightly stale data, asynchronous replication lag is acceptable. Option B is correct because upgrading to a larger instance class with more vCPUs and memory gives the database more CPU and RAM to process complex queries and larger working sets. Option A is correct because tuning the DB parameter group (for example, raising shared_buffers and work_mem) lets PostgreSQL cache more data in memory and allocate more memory per sort/hash operation, which speeds up complex reporting queries. Option D is not appropriate because Multi-AZ provides high availability through a synchronous standby, not read scaling, and the standby is not accessible for reporting queries. Option E is not the best fit because ElastiCache caches application-level query results rather than addressing the database's read performance for complex queries, and it adds complexity without directly scaling the RDS read workload.

Answer

Enable Multi-AZ on the RDS instance.

Answer

Implement an Amazon ElastiCache cluster to cache query results.

Question 14

A company uses Amazon RDS for MySQL with Multi-AZ and read replicas. The database has a table storing user sessions with 50 million rows. The application team reports that queries using 'SELECT * FROM sessions WHERE user_id = ? ORDER BY login_time DESC LIMIT 10' are slow. The EXPLAIN plan shows a full table scan. Which design change would BEST improve query performance?

Accepted Answer

Create a composite index on (user_id, login_time). The query filters on user_id and orders by login_time, which is a classic case for a composite index. A B-Tree index on (user_id, login_time) allows MySQL to locate all rows for the given user_id via the index's leading column and then retrieve the rows in sorted order using the second column, avoiding a full table scan and a filesort operation. This directly addresses the root cause — the lack of an index to support both the WHERE and ORDER BY clauses efficiently.

Answer

Implement an application-level cache using ElastiCache

Answer

Partition the table by user_id

Answer

Upgrade to a larger instance type with more memory

Question 15

A company is migrating an on-premises Oracle database to AWS. The database is 5 TB and supports a critical OLTP application with high transaction rates. The application requires stored procedures, triggers, and strong consistency. Which AWS database service is most appropriate with minimal application changes?

Accepted Answer

Amazon RDS for Oracle. Amazon RDS for Oracle is the most appropriate choice because it provides native Oracle compatibility, supporting stored procedures, triggers, and strong consistency with minimal application changes. The company can use Oracle's PL/SQL code directly, and RDS for Oracle offers full ACID compliance for OLTP workloads, avoiding the need to rewrite application logic or adapt to a different consistency model.

Answer

Amazon Aurora PostgreSQL

Answer

Amazon DynamoDB

Answer

Amazon Redshift

Question 16

A company needs to store and query time-series data from IoT sensors. The data is written continuously and queried by time range for dashboards. Which AWS database service is most cost-effective and scalable for this workload?

Accepted Answer

Amazon Timestream.. Amazon Timestream is purpose-built for time-series data, offering automatic tiering between in-memory and magnetic stores for cost efficiency, and built-in functions for time-based aggregations and windowed queries. It is serverless and scales automatically to handle continuous writes from IoT sensors and low-latency dashboard queries by time range, making it the most cost-effective and scalable choice.

Answer

Amazon ElastiCache for Redis with time-series data structures.

Answer

Amazon DynamoDB with time-based partition keys.

Answer

Amazon RDS for PostgreSQL with time-based indexing.

Question 17

A company uses Amazon RDS for Oracle for an OLTP application. The database experiences high CPU utilization during peak hours. The application is read-heavy and can tolerate eventually consistent reads. Which solution reduces CPU load on the primary database with minimal application changes?

Accepted Answer

Create an RDS read replica and direct read traffic to it. Creating an RDS Read Replica offloads read traffic from the primary Oracle instance, directly reducing CPU utilization on the primary. Since the application is read-heavy and tolerates eventually consistent reads, the replica’s asynchronous replication lag is acceptable. This solution requires minimal application changes—only modifying the connection string to route SELECT queries to the replica endpoint.

Answer

Implement Amazon ElastiCache to cache frequent queries

Answer

Upgrade to a larger instance type

Answer

Use DynamoDB Accelerator (DAX) as a cache layer

Question 18

A company is designing a document storage system using Amazon DynamoDB. Each document is up to 400 KB and is identified by a unique 'document_id'. The access pattern is to retrieve a document by its ID. Which DynamoDB table design is MOST efficient?

Accepted Answer

Use 'document_id' as the primary partition key (only).. DynamoDB can store items up to 400 KB in a single table, and using 'document_id' as the sole partition key directly supports the access pattern of retrieving a document by its ID with a single GetItem call, which is the most efficient operation. No secondary index or composite key is needed, as the primary key alone provides O(1) lookup performance for this use case.

Answer

Use 'document_id' as the partition key and create a GSI on 'document_id'.

Answer

Store documents in Amazon S3 and use DynamoDB to store metadata with a reference to S3.

Answer

Use a composite key: partition key 'document_id' and sort key 'version'.

Question 19

Refer to the exhibit. An IAM policy is attached to a user. The user tries to delete a database instance named 'prod-mydb' in us-east-1. What will happen?

Accepted Answer

The delete will be denied because the Deny statement explicitly matches the resource.. D is correct because IAM policy evaluation follows an explicit deny priority rule. Even though the Allow statement grants 'rds:DeleteDBInstance' on 'arn:aws:rds:us-east-1:*:db:*', the Deny statement explicitly matches the resource 'arn:aws:rds:us-east-1:123456789012:db:prod-mydb' and specifies 'rds:DeleteDBInstance'. Since an explicit deny overrides any allow, the delete operation will be denied.

Answer

The delete will be allowed because the Allow statement is broader.

Answer

The delete will fail with an error because the policy is invalid.

Answer

The delete will succeed only if the instance is tagged with 'Environment: prod'.

Question 20

A company is using Amazon DynamoDB with provisioned capacity. The table's read capacity is consistently underutilized, but the write capacity is frequently maxed out. The team wants to optimize costs while maintaining performance. Which TWO actions should be taken?

Accepted Answer

Use DynamoDB Auto Scaling for write capacity.. Option C is correct because DynamoDB Auto Scaling can dynamically adjust the table's provisioned write capacity in response to actual consumed write throughput, scaling up during spikes and back down when demand drops, which directly addresses the frequently maxed-out write capacity while avoiding over-provisioning costs. Option E is correct because the read capacity is consistently underutilized, so lowering the provisioned read capacity to match real consumption eliminates paying for unused RCUs and reduces cost without harming performance. Option A is not appropriate because switching to on-demand mode changes the billing model entirely and is not the targeted optimization for a table with a known, asymmetric read/write pattern under provisioned capacity. Option B does not belong because DAX only accelerates and offloads read traffic, and reads are already underutilized, so it would add cost without fixing the write bottleneck. Option D is not ideal because simply increasing provisioned write capacity to handle spikes is a static, manual change that raises cost rather than optimizing it, whereas Auto Scaling adjusts capacity automatically.

Answer

Switch the table to on-demand capacity mode.

Answer

Enable DynamoDB Accelerator (DAX) to offload reads.

Answer

Increase the provisioned write capacity to handle spikes.