DBS-C01 Practice Test 50 — 15 Questions

Question 1

A company is migrating a 2 TB SQL Server database to Amazon RDS for SQL Server. They need to minimize downtime and are using AWS DMS with CDC. The migration is taking longer than expected during the full load phase. Which change would most likely improve the full load performance?

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

Accepted Answer

Increase the number of parallel load tasks in the DMS task settings. Increasing the number of parallel load tasks in the DMS task settings allows the full load to be split into multiple concurrent threads, each handling a subset of tables or partitions. This directly improves throughput by utilizing more of the available source and target resources, which is the most effective way to accelerate a slow full load phase when using AWS DMS with CDC.

Answer

Disable CDC to focus on full load only

Answer

Use AWS Schema Conversion Tool to optimize schema

Answer

Use a larger RDS instance class for the target

Question 2

A company is deploying a new Amazon RDS for Oracle instance and needs to ensure high availability and automatic failover. Which configuration should be used?

Accepted Answer

Multi-AZ deployment. (Multi-AZ deployment) is correct because it provisions a synchronous standby replica in a different Availability Zone, enabling automatic failover without data loss when the primary instance fails. This meets the high availability and automatic failover requirements for Amazon RDS for Oracle. Option D (Automated backups with point-in-time recovery) provides backup and recovery capabilities but does not ensure high availability or automatic failover; it is not a configuration for automatic failover.

Answer

Read Replicas in a different Region

Answer

Enhanced Monitoring

Answer

Automated backups with point-in-time recovery

Answer

Deletion protection

Question 3

A company is using Amazon DynamoDB as the primary database for a global e-commerce application. During the holiday season, the application experiences throttling on write requests even though the read and write capacity units are well below the provisioned limits. The table uses on-demand capacity mode. What is the most likely cause of this throttling?

Accepted Answer

There is a hot partition due to an uneven write distribution across partition keys.. In DynamoDB on-demand capacity mode, throughput scales automatically based on traffic. However, throttling can still occur if a single partition receives more write requests than the partition's maximum throughput capacity (1,000 WCU per partition). This is known as a hot partition, caused by an uneven distribution of write activity across partition keys. Option A correctly identifies this. Option B is incorrect because on-demand mode does not use provisioned capacity. Option C uses incorrect terminology—there is no 'maximum write capacity units per partition' that the table as a whole can exceed. Option D is incorrect because DynamoDB does not have a per-region account-level write limit that causes throttling on a single table.

Answer

The table's provisioned write capacity is set too low.

Answer

The table has exceeded the maximum write capacity units per partition.

Answer

The AWS account has reached the DynamoDB write throughput limit per region.

Question 4

A company is designing a data lake on Amazon S3 with Amazon Redshift Spectrum for analytics. The data includes JSON logs from web servers. Which THREE design practices should the company follow to optimize query performance and cost?

Accepted Answer

Compress files using gzip or snappy.. Compressing JSON files with gzip or Snappy reduces the data size stored in S3, lowering storage costs and minimizing the amount of data that Redshift Spectrum must scan over the network. Redshift Spectrum can read compressed files directly, and compression often improves query performance by reducing I/O, even though it adds a small CPU overhead for decompression.

Answer

Use many small files to maximize parallelism.

Answer

Create indexes on the S3 data using AWS Glue.

Question 5

A database specialist sees the above output for an RDS MySQL instance. The application reports that the instance is not accepting writes. What is the most likely cause?

Accepted Answer

The instance is a read replica and cannot accept write requests.. The most likely cause is that the RDS MySQL instance is configured as a read replica. Read replicas in Amazon RDS are designed to handle read traffic only and do not accept write operations. Any attempt to write to a read replica will be rejected by the database engine, which matches the symptom described.

Answer

The allocated IOPS are insufficient for the write workload.

Answer

Multi-AZ is not enabled, so the instance cannot accept writes.

Answer

Storage encryption is enabled, which prevents write operations.

Question 6

A company is migrating a MySQL database to Amazon Aurora MySQL. The migration must be completed with minimal downtime. Which TWO methods can achieve this? (Choose two.)

Accepted Answer

Create an Aurora MySQL read replica from the external MySQL instance using binlog replication. Option A is correct because Aurora MySQL supports creating an Aurora read replica from an external MySQL instance using binary log (binlog) replication, which continuously replicates changes from the source to Aurora and allows a controlled cutover with minimal downtime. Option D is correct because AWS DMS can perform a full load plus ongoing change data capture (CDC) replication from MySQL to Aurora MySQL, keeping the target in sync until you are ready to switch over. Option E is not a complete method by itself; enabling binlog on the source is only a prerequisite for replication, not a migration solution. Option B is wrong because a physical backup and restore requires taking the source offline and does not support continuous replication, causing downtime. Option C is wrong because Aurora cloning works only from an existing Aurora or Amazon RDS source within AWS, not from an external MySQL database.

Answer

Take a physical backup of the source database and restore to Aurora

Answer

Create an Aurora clone from the source database

Answer

Enable binlog replication on the source MySQL instance

Question 7

A database administrator needs to track changes to an Amazon RDS DB instance's configuration, such as modifications to the DB instance class or security group. Which AWS service should be used?

Accepted Answer

AWS Config. AWS Config is the service designed to record and evaluate the configuration of AWS resources, including RDS DB instances. It continuously monitors and records changes to configurations such as DB instance class, security groups, and other settings. AWS Config can also evaluate these configurations against desired policies, making it the correct choice for tracking configuration changes.

Answer

Amazon CloudWatch Logs

Answer

AWS CloudTrail

Answer

AWS Systems Manager Patch Manager

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 C is correct because AWS DMS with ongoing replication (change data capture) continuously applies source changes to the Aurora PostgreSQL target, allowing a cutover with minimal downtime rather than a one-time bulk load. Option D is correct because AWS DMS data validation compares rows between the Oracle source and Aurora target and reports mismatches, directly satisfying the requirement to validate data consistency after migration. Option E is correct because Oracle-to-Aurora PostgreSQL is a heterogeneous migration, and AWS SCT converts the Oracle schema, data types, and PL/SQL objects into PostgreSQL-compatible DDL before DMS moves the data. Option A is not required: Aurora Replicas provide read scaling and high availability but do not address migration downtime or consistency validation. Option B is not appropriate because Oracle-to-Aurora PostgreSQL is a heterogeneous migration, so a homogeneous migration path does not apply.

Answer

Create multiple Aurora Replicas for read scaling during migration.

Answer

Perform a homogeneous migration directly from Oracle to Aurora.

Question 9

A financial services company uses Amazon DynamoDB to store transaction records. Each transaction has a unique transaction_id as the partition key and a timestamp as the sort key. The application frequently queries all transactions for a given customer within a date range. However, customer_id is not an attribute indexed for querying. The company wants to optimize these queries without redesigning the entire table schema. Which action should the company take?

Accepted Answer

Create a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key.. Creating a Global Secondary Index (GSI) with customer_id as the partition key and timestamp as the sort key allows efficient querying of all transactions for a given customer within a date range without redesigning the base table. The GSI provides a new access pattern with its own partition and sort keys, enabling the Query operation on customer_id and timestamp, which is far more efficient than a Scan. This approach preserves the existing table schema and supports the required query pattern with minimal overhead.

Answer

Change the table's partition key to customer_id and use a composite sort key.

Answer

Create a Local Secondary Index (LSI) on customer_id.

Answer

Use the Scan operation with a filter expression for customer_id and timestamp.

Question 10

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).. Option C is correct because time-series workloads such as IoT sensor data generate continuous high-volume writes, and configuring automatic data expiration using TTL (Time-to-Live) enables efficient data retention by automatically removing stale records without manual deletion jobs. Option D is correct because partitioning the table by time intervals (e.g., hourly or daily) improves write throughput and query efficiency by localizing writes and enabling fast pruning of old time ranges during retention operations. Option E is correct because Amazon Timestream is a purpose-built time-series database with built-in optimizations such as time-based partitioning, memory-store/ magnetic-store tiering, and automatic data lifecycle management, making it well suited for high-ingest IoT workloads. Option A is not appropriate because normalizing the schema to reduce duplication is a relational OLTP design practice that adds joins and overhead, which harms the high write throughput and time-ordered access patterns typical of time-series data. Option B is not appropriate because Amazon RDS Proxy manages and pools database connections for relational databases, but it does not address time-series storage, write throughput optimization, or data retention requirements.

Answer

Normalize the schema to reduce data duplication.

Answer

Use Amazon RDS Proxy to manage database connections.

Question 11

A company is using Amazon RDS for MariaDB. The database administrator wants to monitor the database for slow queries. Which TWO services can be used to achieve this? (Choose TWO.)

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights (A) is correct because it provides a visual dashboard that shows database load and helps identify the top SQL statements contributing to load, making it ideal for pinpointing slow queries on an RDS for MariaDB instance. Amazon CloudWatch Logs (C) is correct because RDS for MariaDB can publish the slow query log and error log to CloudWatch Logs, where you can search and analyze entries to find queries exceeding the long_query_time threshold. AWS Config (B) is incorrect because it records resource configuration changes and compliance, not query performance. Amazon RDS Enhanced Monitoring (D) is incorrect because it reports OS-level metrics such as CPU, memory, and disk I/O, not individual slow SQL statements. AWS CloudTrail (E) is incorrect because it logs API activity and management events, not database query execution times.

Answer

AWS Config

Answer

Amazon RDS Enhanced Monitoring

Answer

AWS CloudTrail

Question 12

A company has a document database workload on Amazon DynamoDB that stores user session data. The application frequently updates session attributes (e.g., last activity timestamp). The current design stores the entire session as a single item and updates the entire item on each session activity. This is causing high write costs and throttling. Which design pattern would reduce write costs and improve performance?

Accepted Answer

Use UpdateItem with an update expression to modify only the changed attributes.. Using UpdateItem with an update expression allows you to modify only the specific attributes that changed (e.g., last activity timestamp) instead of rewriting the entire item. This reduces write consumption to a fraction of the original cost, since DynamoDB charges based on the size of the written data, and partial updates write only the changed attribute bytes. This directly addresses the high write costs and throttling caused by full-item overwrites.

Answer

Increase the write capacity units (WCUs) on the table.

Answer

Implement DynamoDB Accelerator (DAX) to cache the session data.

Answer

Split the session item into multiple items, one per attribute.

Question 13

A company is using Amazon ElastiCache for Redis as a caching layer for a web application. The application's response time has increased, and the operations team suspects that cache evictions are occurring frequently. Which ElastiCache metric should be monitored to confirm cache evictions?

Accepted Answer

Evictions. The Evictions metric in Amazon ElastiCache for Redis shows the number of keys evicted due to memory pressure. Option A (CacheHits) is wrong because it indicates successful key retrievals, not evictions. Option B (SwapUsage) is wrong because it shows the amount of swap space used, not eviction count. Option D (CurrItems) is wrong because it shows the current number of items in the cache, not evictions.

Answer

CacheHits

Answer

SwapUsage

Answer

CurrItems

Question 14

A developer is using AWS Database Migration Service (DMS) to migrate a database from on-premises to Amazon RDS. The migration task is failing with 'Insufficient memory' error. Which resource should be increased to resolve this?

Accepted Answer

Increase the size of the DMS replication instance.. AWS DMS runs the migration task on a dedicated replication instance, and the 'Insufficient memory' error indicates that the replication instance's memory is exhausted while buffering change data capture (CDC) or full-load rows. Increasing the replication instance class (more RAM) directly resolves this. The source, target, and S3 staging resources are not where DMS allocates its task memory.

Answer

Increase the memory on the source database.

Answer

Increase the Amazon S3 bucket size for staging.

Answer

Increase the memory on the target RDS instance.

Question 15

A gaming company needs a database to store player session data that is ephemeral and requires sub-millisecond latency. The data can be lost on failure without impact. Which service is best?

Accepted Answer

Amazon ElastiCache for Redis. Amazon ElastiCache for Redis is the best choice because it provides an in-memory data store with sub-millisecond latency, ideal for ephemeral player session data that can be lost on failure. Redis supports data structures like strings and hashes with TTL (time-to-live) expiration, perfectly matching the transient, low-latency requirement without needing durability.

Answer

Amazon DynamoDB

Answer

Amazon RDS for PostgreSQL

Answer

Amazon S3