DBS-C01 Timed Practice Test 5 — 10 Questions

Question 1

A social media analytics company uses Amazon DynamoDB as the primary data store for user session data. Each session record has a partition key of user_id (String) and a sort key of session_start_time (Number, epoch). The application often queries the most recent 10 sessions for a given user. The traffic pattern shows that 90% of reads are for the last 10 sessions, while 10% are for historical sessions. The table has a provisioned read capacity of 5000 RCU and consistently experiences throttled read requests during peak hours. The company wants to optimize read performance without changing the provisioned capacity. Which design change will MOST improve read performance for this workload?

Accepted Answer

Create a Global Secondary Index (GSI) with the same partition key and a sort key of session_start_time, but query with ScanIndexForward=false and Limit=10.. Option A is correct because creating a GSI with the same partition key (user_id) and sort key (session_start_time) allows you to query with ScanIndexForward=false and Limit=10 to efficiently retrieve only the most recent 10 sessions per user. This avoids scanning all sessions for a user, reducing consumed read capacity and eliminating throttling without increasing provisioned RCU. The GSI also supports the 90% workload pattern by providing a targeted index that minimizes read unit consumption.

Answer

Increase the provisioned read capacity to 10000 RCU to handle the peak load.

Answer

Enable DynamoDB Accelerator (DAX) with default settings to cache the most recent sessions.

Answer

Configure Amazon ElastiCache for Redis as a read-through cache for session data.

Question 2

A company is designing a new e-commerce platform using Amazon DynamoDB. The workload requires single-digit millisecond latency for user session data, which is accessed by session token. The session data is temporary and should be automatically deleted after 24 hours. Which DynamoDB design should the database specialist recommend?

Accepted Answer

Enable DynamoDB Time to Live (TTL) on the session token attribute. DynamoDB Time to Live (TTL) automatically deletes expired items after a specified timestamp, making it ideal for session data that must be removed after 24 hours. This approach requires no additional infrastructure, meets the single-digit millisecond latency requirement by using the session token as the primary key, and ensures automatic cleanup without manual intervention or added cost.

Answer

Create an AWS Lambda function that runs every hour and deletes expired session data

Answer

Store session data in Amazon S3 with a lifecycle policy to delete objects after 24 hours

Answer

Use DynamoDB Accelerator (DAX) to cache session data and set a 24-hour TTL on the cache

Question 3

A company is running a critical application on Amazon DynamoDB. The table has a partition key of 'user_id' and a sort key of 'timestamp'. The application frequently queries for all items for a given user within a date range. The read capacity is often throttled during peak hours. Which THREE steps should the database specialist take to resolve the throttling?

Accepted Answer

Enable DynamoDB adaptive capacity to automatically adjust throughput. Option A is correct because DynamoDB adaptive capacity automatically manages throughput to accommodate uneven access patterns, such as when a single 'user_id' partition receives more reads than provisioned. It allows the table to absorb throttling by redistributing unused capacity from other partitions, which directly addresses the peak-hour throttling without manual intervention.

Answer

Change the partition key to 'timestamp' to improve read distribution

Answer

Decrease the provisioned write capacity units (WCU) to free up resources for reads

Question 4

A company is designing a multi-tenant SaaS application on Amazon Aurora MySQL. Each tenant has its own database, but some tenants are very large and generate high write traffic. The company wants to isolate tenant workloads to prevent a noisy neighbor from affecting other tenants. Which TWO design strategies should the database specialist recommend?

Accepted Answer

Use Aurora Serverless for tenants with variable workloads. Option A is correct because Aurora Serverless automatically scales compute capacity based on application demand, which is ideal for tenants with variable workloads. This prevents a noisy neighbor scenario by ensuring that a tenant's burst of write traffic does not consume shared resources that would degrade performance for other tenants.

Answer

Use a single Aurora cluster with read replicas for each tenant

Answer

Migrate all tenants to Amazon DynamoDB and use DynamoDB Accelerator (DAX) for caching

Answer

Use Amazon RDS Proxy to pool connections and limit throughput per tenant

Question 5

A financial services company is migrating its Oracle database to Amazon Aurora PostgreSQL. The database runs a critical batch processing job every night that updates millions of rows. The company needs the migration to minimize downtime and ensure data integrity. Which AWS service should the database specialist use to perform the migration?

Accepted Answer

AWS Database Migration Service (AWS DMS) with ongoing replication from Oracle to Aurora PostgreSQL. AWS DMS with ongoing replication (change data capture, CDC) is the correct choice because it enables a near-zero-downtime migration by continuously replicating changes from the source Oracle database to the target Aurora PostgreSQL while the source remains fully operational. After the initial full load, DMS applies ongoing transactions, allowing you to cut over with minimal interruption. This directly addresses the requirement to minimize downtime for the nightly batch job and ensures data integrity through transactional consistency.

Answer

AWS Data Pipeline to export data from Oracle and import into Aurora PostgreSQL

Answer

AWS Schema Conversion Tool (AWS SCT) to convert the schema and then use native PostgreSQL tools to migrate data

Answer

AWS Glue to extract data from Oracle and load into Aurora PostgreSQL

Question 6

A company is designing a multi-tenant SaaS application on Amazon RDS for PostgreSQL. Each tenant's data must be isolated for security and performance. The application has millions of tenants, with most tenants having small datasets (under 100 MB). Which database design pattern is MOST cost-effective and operationally efficient?

Accepted Answer

Use a single RDS instance with a shared schema and implement Row-Level Security (RLS) policies based on tenant_id.. Option B is correct because using a single RDS for PostgreSQL instance with Row-Level Security (RLS) allows you to isolate tenant data at the row level based on a tenant_id column, without the overhead of managing millions of separate schemas or tables. This design is both cost-effective (single instance, no per-tenant provisioning) and operationally efficient (simple schema management, no connection pooling issues), while still meeting security and performance isolation requirements for small datasets under 100 MB.

Answer

Use Amazon DynamoDB with a separate table per tenant.

Answer

Use a single RDS instance with a separate schema per tenant.

Answer

Use a separate Amazon RDS for PostgreSQL instance per tenant.

Question 7

A company is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database has a large table that is frequently accessed by reporting queries. The reporting queries filter on a column that has a high cardinality but low selectivity. To optimize query performance on this table, which design choice should the database specialist recommend?

Accepted Answer

Create a covering index on the filter column. Option D is correct because a covering index includes all columns needed by the reporting queries, allowing PostgreSQL to satisfy the query entirely from the index without accessing the heap (table) pages. This eliminates the overhead of random I/O for row lookups, which is especially beneficial when filtering on a high-cardinality, low-selectivity column where many rows match but the index scan alone can return the required data. In Amazon RDS for PostgreSQL, this reduces read IOPS consumption and improves query latency.

Answer

Partition the table by the filter column

Answer

Use a read replica to offload reporting queries

Answer

Increase the provisioned read IOPS for the RDS instance

Question 8

A social media application uses Amazon DynamoDB as its primary data store. The application stores user posts and allows users to retrieve the most recent 10 posts of users they follow. The access pattern is a followee-based query that needs to be highly scalable and low-latency. Which DynamoDB table design should the database specialist recommend?

Accepted Answer

Use a composite primary key with a partition key of follower ID and a sort key of timestamp, and store the followee ID as an attribute. Option C is correct because it models the access pattern directly: the follower ID as the partition key ensures all posts from followed users are co-located, and the sort key of timestamp allows efficient retrieval of the most recent 10 posts via a Query with a limit of 10 and descending order. This design avoids expensive scans or secondary index lookups, meeting the low-latency and scalability requirements.

Answer

Use a partition key of post ID and a local secondary index on the followee ID

Answer

Use a single table with a scan operation and filter on the followee attribute

Answer

Design the table with a partition key of user ID and a sort key of timestamp, and create a global secondary index (GSI) on followee ID

Question 9

A gaming company uses Amazon DynamoDB for player session data. Each session has a partition key of `game_id` and a sort key of `session_id`. The table has a global secondary index (GSI) on `player_id` for leaderboard queries. Recently, the company noticed that write traffic to the GSI is causing throttling on the base table, even though the base table's write capacity is not fully utilized. What is the MOST likely cause?

Accepted Answer

The GSI is not designed with a high-cardinality partition key, causing write hot spots on the GSI.. The correct answer is B. A global secondary index (GSI) has its own provisioned read and write capacity, separate from the base table. If the GSI's partition key (player_id) has low cardinality (e.g., only a few distinct player_id values), writes to the base table will concentrate on a small number of GSI partitions, causing throttling on the GSI. This throttling on the GSI then back-pressures the base table, resulting in write throttling on the base table even if its own write capacity is underutilized.

Answer

The application is using strongly consistent reads on the GSI, which consumes double the read capacity.

Answer

Point-in-time recovery (PITR) is enabled, consuming extra write capacity.

Answer

The table's auto-scaling settings are not configured correctly for the GSI.

Question 10

A company is migrating a 500 GB MySQL database from on-premises to Amazon RDS for MySQL. The migration must have minimal downtime and support ongoing replication. Which AWS service should be used?

Accepted Answer

Use AWS Database Migration Service (DMS) with a full load and ongoing replication from a change data capture source.. AWS DMS is the correct choice because it supports both a full load of the 500 GB database and ongoing replication using change data capture (CDC) from the on-premises MySQL source. This enables minimal downtime by keeping the target RDS instance synchronized during the migration window, and it handles schema conversion automatically for MySQL-to-MySQL migrations without needing a separate tool.

Answer

Use mysqldump to export the database and import to RDS during a maintenance window.

Answer

Use AWS Schema Conversion Tool (SCT) to convert the schema and migrate data.

Answer

Take a physical backup, copy it to Amazon S3, and restore to RDS.