DBS-C01 Practice Exam 60 — 20 Questions

Question 1

A company has an Amazon Redshift cluster with two dc2.large nodes. The cluster is used for daily ETL jobs and reporting. The operations team receives an alert that the cluster's disk space is 90% full. The ETL jobs are failing with 'disk full' errors. The team needs to resolve the issue quickly with minimal downtime. Which action should be taken?

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

Accepted Answer

Resize the cluster to a larger node type, such as dc2.large to ds2.xlarge, or add more nodes.. Resizing the cluster to a larger node type or adding more nodes increases the total storage capacity, directly addressing the disk full issue. Option A is wrong because a deep copy reorganizes data but does not increase storage capacity. Option B is wrong because VACUUM reclaims space from deleted rows but may not free enough space when the cluster is already 90% full. Option D is wrong because unloading data to S3 removes data from the cluster only if deleted, but the statement does not include deletion; even if deleted, the space is not reclaimed until VACUUM.

Answer

Perform a deep copy to re-sort and reclaim space.

Answer

Run the VACUUM command to reclaim space from deleted rows.

Answer

Unload old data to Amazon S3 and delete from the cluster.

Question 2

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The security team wants to ensure that database administrators cannot view sensitive data. Which TWO actions should be taken to achieve this goal?

Accepted Answer

Use IAM database authentication for application access.. IAM database authentication allows you to authenticate to your RDS MySQL instance using an IAM user or role instead of a traditional database password. This eliminates the need for database administrators to know or manage database credentials, as they can only access the database through IAM policies that grant specific, auditable permissions. By using IAM authentication, you enforce a separation of duties where DBAs cannot view sensitive data unless explicitly authorized by IAM policies.

Answer

Enable audit logging to capture all data access.

Answer

Enable encryption at rest using a customer-managed KMS key.

Answer

Disable query logging to prevent sensitive data from being written to logs.

Question 3

Refer to the exhibit. A database administrator runs the AWS CLI command shown. The output is: ["available", false]. What does this output indicate about the DB instance?

Accepted Answer

The DB instance is available and is not configured for Multi-AZ.. The output shows the DBInstanceStatus is 'available' and MultiAZ is false. Option A is incorrect because MultiAZ false indicates it is not in the process of being modified to enable Multi-AZ. Option B is incorrect because MultiAZ is false, meaning it is not in a Multi-AZ deployment. Option C is incorrect because the status is 'available', not 'stopped'.

Answer

The DB instance is in the process of being modified to enable Multi-AZ.

Answer

The DB instance is in a Multi-AZ deployment and is available.

Answer

The DB instance is stopped and is not in a Multi-AZ configuration.

Question 4

A company is using Amazon DynamoDB with on-demand capacity. The application performs many small writes that are throttled frequently. The company wants to minimize costs while reducing throttling. What should the company do?

Accepted Answer

Switch to provisioned capacity with auto scaling.. DynamoDB on-demand capacity can throttle small writes if the traffic pattern exceeds the table's previous peak traffic, as on-demand capacity scales based on traffic volume but has a per-second burst limit. Switching to provisioned capacity with auto scaling allows you to set a baseline capacity that matches the application's average write throughput, while auto scaling adjusts capacity based on actual usage, reducing throttling without the premium cost of on-demand capacity for predictable workloads.

Answer

Increase the write capacity units manually.

Answer

Use DynamoDB Accelerator (DAX) to cache writes.

Answer

Use batch writes to combine small writes.

Question 5

A company needs to build a reporting dashboard that queries a large dataset stored in Amazon S3. The queries are complex and require full SQL support. Which service should be used?

Accepted Answer

Amazon Athena. Amazon Athena is the correct choice because it is a serverless, interactive query service that allows you to analyze data directly in Amazon S3 using standard SQL. It supports complex queries, including joins, window functions, and CTEs, and requires no infrastructure management, making it ideal for ad-hoc reporting on large datasets in S3.

Answer

Amazon Redshift Spectrum

Answer

Amazon RDS

Answer

Amazon DynamoDB

Question 6

A company has an Amazon DynamoDB table with on-demand capacity mode. The table experiences a sudden spike in traffic, and the application starts receiving ProvisionedThroughputExceededException errors. What is the most likely cause?

Accepted Answer

The traffic spike exceeded the previous peak traffic by more than double in a short period. DynamoDB on-demand capacity mode can throttle requests if the traffic spike exceeds the previous peak traffic by more than double within a short period. This is due to the adaptive capacity mechanism that requires time to scale. Option A is wrong because on-demand mode does not have provisioned read/write capacity units. Option B is wrong because on-demand mode does not have a maximum number of capacity units; it scales automatically but with a ramp-up limit. Option D is wrong because Auto Scaling is not applicable to on-demand mode; it uses a different scaling model.

Answer

The provisioned read capacity units are insufficient

Answer

The table has reached the maximum number of read capacity units

Answer

Auto Scaling is not configured to increase capacity

Question 7

A logistics company operates a fleet tracking system using Amazon DocumentDB (with MongoDB compatibility). The database stores location updates from thousands of vehicles every second. The collection has a compound index on (vehicle_id, timestamp). Recently, the company noticed that write latency has increased, and the primary instance's CPU is consistently above 80%. The storage is gp2, and the instance is a db.r5.large. The operations team suspects that index maintenance is causing high CPU. The database administrator needs to reduce write latency without sacrificing query performance for real-time location queries. What should the administrator do?

Accepted Answer

Shard the collection using a hash-based shard key on vehicle_id to distribute write load.. Sharding the collection using a hash-based shard key on vehicle_id distributes writes evenly and reduces index maintenance overhead. Option A is wrong because removing the compound index harms query performance for real-time location queries. Option B is wrong because upgrading to a larger instance class adds CPU but does not address the root cause of index maintenance overhead. Option C is wrong because disabling journaling reduces durability, not index maintenance.

Answer

Remove the compound index and rely on the default _id index for queries.

Answer

Upgrade to a larger instance class, such as db.r5.xlarge, to provide more CPU and memory.

Answer

Disable journaling to reduce write I/O.

Question 8

A developer needs to allow an application running on an EC2 instance to connect to an Amazon RDS for MySQL DB instance securely. Which combination of steps should the developer take?

Accepted Answer

Attach an IAM role to the EC2 instance with permissions to use RDS IAM authentication, and configure the database to use an authentication token.. The most secure method to allow an EC2 instance to connect to an RDS for MySQL DB instance is to use IAM roles for EC2 combined with IAM database authentication. By attaching an IAM role to the EC2 instance that has permissions to generate RDS authentication tokens, and configuring the DB instance to accept authentication tokens instead of passwords, the application can obtain temporary credentials without hardcoding or storing any secrets. Option A is insecure because storing credentials in application code exposes them to anyone with access to the code. Option B is insecure because opening the security group to all traffic (0.0.0.0/0) exposes the database to the internet. Option C is insecure because storing credentials in S3 and downloading them at runtime still involves storing static credentials and adds potential risk from S3 access misconfiguration.

Answer

Store the database password in the application code.

Answer

Open the RDS security group to allow traffic from 0.0.0.0/0.

Answer

Store the credentials in an S3 bucket and download them at runtime.

Question 9

A company runs a document database using Amazon DocumentDB. They notice that some queries are taking much longer than expected. The explain plan shows a COLLSCAN. Which action would most improve query performance?

Accepted Answer

Create appropriate indexes on the fields used in query filters. Creating appropriate indexes on the fields used in query filters is the most effective action to improve performance because it eliminates the need for a COLLSCAN (collection scan). Increasing instance size (option A) may help but does not address the root cause of missing indexes. Changing read consistency from eventual to strong (option B) affects the freshness of reads, not query performance. Increasing storage (option C) does not improve query speed; it only provides more space for data.

Answer

Increase the instance size to the next tier

Answer

Change the read consistency from eventual to strong

Answer

Increase the storage allocated to the instance

Question 10

Which THREE factors should be considered when choosing between Amazon RDS Multi-AZ and Amazon Aurora for high availability? (Choose 3)

Accepted Answer

Aurora provides faster failover (typically under 30 seconds). Aurora's distributed storage architecture enables failover in under 30 seconds typically, because the storage layer is shared across all instances in the cluster. When the primary instance fails, Aurora simply promotes one of the existing read replicas to primary, without needing to remap storage volumes. This is significantly faster than RDS Multi-AZ, which requires a DNS change and a synchronous block-level replication failover that can take 60-120 seconds.

Answer

RDS Multi-AZ provides automatic scaling of storage

Answer

RDS Multi-AZ supports encryption at rest

Question 11

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. During the migration, they need to ensure minimal downtime. Which AWS service should be used for the migration?

Accepted Answer

AWS Database Migration Service. AWS Database Migration Service (DMS) is the correct choice because it is specifically designed for migrating databases to AWS with minimal downtime. DMS supports homogeneous migrations (e.g., Oracle to Oracle) and heterogeneous migrations (e.g., Oracle to Amazon Aurora), and it can perform continuous replication using change data capture (CDC) to keep the source and target databases synchronized during the migration, allowing you to cut over with only a brief pause.

Answer

AWS DataSync

Answer

Amazon S3 Transfer Acceleration

Answer

AWS Server Migration Service

Question 12

A company uses Amazon DynamoDB with global tables. During a regional failure, the application in the secondary region experiences higher latency and throttling. The DynamoDB table's WriteCapacityUnits are set to 10000 in both regions. Which action should be taken to reduce throttling during failover?

Accepted Answer

Enable DynamoDB auto scaling for write capacity in both regions. Enabling DynamoDB auto scaling allows the table to dynamically adjust write capacity based on actual traffic, which helps reduce throttling during failover when secondary region traffic increases. Option A is incorrect because switching to on-demand capacity mode may reduce throttling but is more expensive and not the most direct fix for capacity limits; auto scaling provides a more cost-effective solution. Option C is incorrect because disabling global tables would stop cross-region replication, defeating the purpose of multi-region disaster recovery. Option D is incorrect because increasing write capacity of only the secondary region to 20000 may lead to over-provisioning and cost, while auto scaling provides a more efficient and automated solution to handle varying load.

Answer

Switch the table to on-demand capacity mode

Answer

Disable global tables and use application-level replication

Answer

Increase the write capacity of the secondary region to 20000

Question 13

A company is designing a document database for a content management system using Amazon DocumentDB. The application requires high availability and low-latency reads across multiple AWS Regions. Which TWO design choices meet these requirements?

Accepted Answer

Configure read replicas in each region to offload read traffic.. Amazon DocumentDB read replicas can be placed in different AWS Regions to offload read traffic and provide low-latency reads locally. Option D is correct because a global cluster in DocumentDB replicates data from a primary region to secondary regions, enabling high availability and low-latency reads across regions.

Answer

Use a single instance in each region with Multi-AZ disabled.

Answer

Use local secondary indexes to improve query performance in each region.

Answer

Shard the data across multiple clusters in different regions.

Question 14

A database engineer is troubleshooting a production Amazon Aurora MySQL DB cluster. The application is experiencing high latency on write operations. The engineer checks the Amazon CloudWatch metrics and sees that the 'AuroraBinlogReplicaLag' metric is high. What is the most likely cause of the write latency?

Accepted Answer

The binlog replication to a downstream MySQL instance is falling behind. The 'AuroraBinlogReplicaLag' metric specifically measures the lag between the Aurora MySQL cluster and an external MySQL instance that is replicating from Aurora using binary log (binlog) replication. When this lag is high, it indicates that the downstream MySQL instance is falling behind in applying binlog events, which can cause write operations on the Aurora cluster to stall or slow down due to the synchronous nature of binlog generation and the need to retain binlogs until they are consumed by the replica.

Answer

The DB cluster has insufficient storage capacity for the binlog files

Answer

The DB cluster has a high CPU utilization that is causing replication lag

Answer

A recent failover event caused the binlog to be replayed from the last checkpoint

Question 15

A database administrator is troubleshooting a slow-running query on an Amazon RDS for PostgreSQL DB instance. The query plan shows a sequential scan on a large table. The table has a primary key and an index on the column used in the WHERE clause. Why might the query optimizer choose a sequential scan over an index scan?

Accepted Answer

The query is expected to return a large percentage of rows.. When a query is expected to return a large percentage of rows, a sequential scan is often more efficient than an index scan due to the overhead of random I/O from the index. Option B is wrong because the scenario includes a WHERE clause, so SELECT * without WHERE does not apply. Option C is wrong because outdated statistics could cause the optimizer to choose a sequential scan, but the question asks for a reason the planner might choose sequential scan; outdated stats are a possible cause but not the direct reason given in A. Option D is wrong because the index order does not automatically force its use; the optimizer decides based on selectivity.

Answer

The query is a SELECT * without a WHERE clause.

Answer

The table's statistics are outdated.

Answer

The index on the column is not being used because it is a composite index with a different column order.

Question 16

A developer receives a 'ResourceNotFoundException' when trying to describe a DynamoDB table. The developer runs the command shown in the exhibit and gets the output. What is the most likely cause?

Accepted Answer

The developer is using a different AWS region or the table name has incorrect case.. The 'ResourceNotFoundException' indicates the table was not found. The command output lists tables in a specific region. If the table exists in another region, it will not appear. Additionally, DynamoDB table names are case-sensitive. Option A correctly identifies these as the most likely causes. Option B is incorrect because a table not in ACTIVE state would generate a different error. Option C is unlikely because the describe command uses the table name, not the ARN. Option D is incorrect because the describe command succeeded (returned a list), but the specific table was not found due to region or case mismatch.

Answer

The table is not in ACTIVE state.

Answer

The table ARN is incorrect.

Answer

The developer does not have permission to describe the table.

Question 17

A company uses Amazon DynamoDB to store session data for a web application. The security team discovers that an IAM user has been performing unauthorized scans on the table. They need to implement controls to detect and prevent such unauthorized access in the future. Which THREE actions should the security team take? (Choose THREE.)

Accepted Answer

Enable AWS CloudTrail logging and create a metric filter for Scan API calls.. Options A, B, and D are correct. Option A: Enabling CloudTrail logging and creating a metric filter for Scan API calls allows the security team to detect unauthorized scan attempts in real time and trigger alerts. Option B: Using fine-grained access control with IAM conditions (e.g., 'dynamodb:LeadingKeys' or 'dynamodb:Attributes') restricts access to specific items or attributes, preventing unauthorized scans from retrieving sensitive data. Option D: Creating an IAM policy that denies the 'Scan' action for unauthorized users using a condition key (e.g., 'aws:SourceIp' or custom tag) provides a preventive control to block unauthorized scans at the API level. Option C is incorrect because disabling the Scan operation on the DynamoDB table would break legitimate use cases that require scanning (e.g., admin queries, reporting) and is not a recommended control. Option E is incorrect because VPC Flow Logs capture network traffic to DynamoDB, not the DynamoDB API operations themselves, so they cannot detect scans.

Answer

Disable the Scan operation on the DynamoDB table.

Answer

Enable VPC Flow Logs to monitor traffic to DynamoDB.

Question 18

A company is using Amazon ElastiCache for Redis to cache database query results. The cache cluster is a single node. The application experiences increased latency when the cache misses. Which TWO actions can improve the cache hit ratio?

Accepted Answer

Increase the Time-to-Live (TTL) for cached items.. Options A and E are correct. Option A: Increasing TTL keeps data in cache longer, reducing cache misses. Option E: Implementing lazy loading populates the cache on read requests, improving hit ratio over time. Option B is wrong because disabling persistence does not affect cache hit ratio. Option C is wrong because decreasing TTL would increase cache misses. Option D is wrong because adding read replicas improves read throughput but does not improve cache hit ratio.

Answer

Disable persistence to free memory.

Answer

Decrease the Time-to-Live (TTL) for cached items.

Answer

Add read replicas to the ElastiCache cluster.

Question 19

A company is using Amazon RDS for MySQL with Multi-AZ deployment. The database experiences a sudden increase in latency and the application reports timeouts. CloudWatch shows elevated 'ReadLatency' and 'WriteLatency' metrics, while 'CPUUtilization' and 'DatabaseConnections' remain normal. Which is the MOST likely cause?

Accepted Answer

A large transaction is being processed. A large transaction can cause increased latency without high CPU or connection count, as it may be waiting on disk I/O or replication. Option A is wrong because a runaway query consuming CPU would show elevated CPUUtilization, which is normal. Option B is wrong because a Multi-AZ failover would cause a brief spike in latency followed by recovery, not sustained latency. Option D is wrong because insufficient provisioned IOPS would typically show BurstBalance or IOPS metrics, not just ReadLatency and WriteLatency.

Answer

A runaway query is consuming CPU resources

Answer

A Multi-AZ failover occurred

Answer

The database has insufficient provisioned IOPS

Question 20

A team is using AWS DMS to migrate a 3 TB Oracle database to Amazon Aurora PostgreSQL. They configured the task as shown. After the full load completes, they notice that the target tables have no indexes, primary keys, or foreign keys. What is the most likely cause?

Accepted Answer

The TargetTablePrepMode is set to DROP_AND_CREATE, which creates tables without indexes or constraints.. When TargetTablePrepMode is set to DROP_AND_CREATE, AWS DMS drops the target table if it exists and then creates a new one using only the basic column definitions from the source. It does not migrate indexes, primary keys, or foreign keys because DMS is not designed to replicate schema objects beyond table structure and data. To preserve constraints and indexes, you must either pre-create them on the target or use a different prep mode like TRUNCATE_BEFORE_LOAD.

Answer

The migration task did not include transformation rules to create indexes and constraints.

Answer

The table selection rule uses wildcards and excludes system tables, which also excludes index definitions.

Answer

The task is using a full load without LOB support, which prevents index creation.