DBS-C01 Mock Exam 83 — 25 Questions

Question 1

A company uses Amazon ElastiCache for Redis as a caching layer for its e-commerce application. Recently, the cache hit ratio has dropped significantly, causing increased database load. The operations team needs to identify which cache keys are being evicted. What should they do?

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

Accepted Answer

Monitor the 'Evictions' metric in Amazon CloudWatch for the ElastiCache cluster.. The 'Evictions' metric in Amazon CloudWatch directly reports the number of keys evicted from the ElastiCache for Redis cluster due to memory pressure. A drop in cache hit ratio often correlates with increased evictions, and monitoring this metric allows the operations team to identify the rate at which keys are being removed. This is the standard, built-in way to observe eviction activity without additional configuration.

Answer

Check the ElastiCache event history for eviction events.

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Enable the 'INFO' command output to be logged to CloudWatch Logs.

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Enable the Redis slow-log to capture eviction commands.

Question 2

A company is deploying a new application that uses Amazon RDS for PostgreSQL. The database must be highly available and fault-tolerant. Which deployment option meets these requirements?

Accepted Answer

Deploy the RDS instance with Multi-AZ configuration. Amazon RDS Multi-AZ deployment automatically provisions and maintains a synchronous standby replica in a different Availability Zone, providing automatic failover in the event of an AZ outage or primary instance failure. This configuration meets the requirements for high availability and fault tolerance by ensuring the database remains accessible with minimal downtime, as the standby replica is kept in sync synchronously and DNS is updated to point to the standby upon failover.

Answer

Deploy the RDS instance in a single Availability Zone

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Deploy the RDS instance across multiple AWS Regions

Answer

Deploy the RDS instance with multiple read replicas

Question 3

A company is migrating a 5 TB MySQL database to Amazon Aurora MySQL. The migration must have zero downtime and the source database is continuously written to. The team plans to use AWS DMS with ongoing replication. However, they notice that the target Aurora instance is not receiving all changes from the source. Which configuration change is most likely required to resolve this?

Accepted Answer

Enable binary logging (binlog) on the source MySQL database with row-based logging.. AWS DMS requires binary logging (binlog) with row-based logging on the source MySQL database to capture ongoing changes for continuous replication. Without binlog enabled, DMS cannot read the change data stream needed to replicate transactions to the target Aurora instance, causing missed changes. This is a mandatory prerequisite for any MySQL-to-Aurora migration using DMS with ongoing replication.

Answer

Create an Amazon RDS read replica of the source database and use it as the source endpoint.

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Set the target table preparation mode to 'Do nothing' in the DMS task.

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Configure a VPC endpoint for the DMS replication instance.

Question 4

A company is running Amazon Redshift and notices that queries are slow. The administrator runs the STL_ALERT_EVENT_LOG and sees many 'Nested Loop Join' alerts. What is the MOST likely cause?

Accepted Answer

Incorrect distribution keys on the tables.. Nested loop joins in Amazon Redshift occur when the query optimizer cannot use a hash join or merge join, often because the data required for the join is not co-located on the same compute nodes. Incorrect distribution keys cause data to be distributed unevenly or in a way that forces large amounts of data to be redistributed across the network, leading to nested loop joins as a fallback. This is the most likely cause because the STL_ALERT_EVENT_LOG specifically flags nested loop joins as a performance issue related to data distribution.

Answer

Insufficient concurrency scaling.

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Incorrect sort keys on the tables.

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Insufficient compression on the tables.

Question 5

A company is migrating a 2 TB Oracle database to Amazon Aurora PostgreSQL using AWS DMS. The migration is taking longer than expected, and the ongoing replication lag is increasing. Which action would MOST likely improve the migration speed?

Accepted Answer

Increase the DMS replication instance size.. Increasing the replication instance size (Option C) directly addresses the root cause of slow migration and increasing replication lag: insufficient compute or network resources on the DMS instance. A larger instance provides more CPU, memory, and network bandwidth, enabling faster full-load processing and more efficient ongoing replication. This is the most effective action when the instance is resource-constrained, which is common with a 2 TB database.

Answer

Enable parallel load on the DMS task.

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Decrease the DMS task's batch size and commit interval.

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Disable the DMS task's logging to reduce overhead.

Question 6

A company uses Amazon DynamoDB with on-demand capacity mode for a critical application. During a marketing campaign, the application experienced throttled requests despite the on-demand mode. The table has a single partition key. The database specialist notices that the throttling occurs sporadically even though overall traffic is within limits. What is the most likely cause?

Accepted Answer

The table's partition key is causing a hot partition, leading to throttling on that partition.. On-demand mode accommodates traffic spikes, but if a single partition key is used, all traffic goes to one partition. DynamoDB partitions data by partition key; a single hot key can throttle requests even if overall throughput is within limits. Provisioned capacity is not used. Auto scaling is not relevant. The partition limit is a hard limit.

Answer

The table's provisioned capacity is set too low.

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The table's auto scaling is not configured correctly.

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The application is exceeding the DynamoDB account-level throughput limits.

Question 7

A company is migrating a 10 TB Amazon RDS for MySQL database to Amazon Aurora MySQL. The migration must have minimal downtime and must support point-in-time recovery for the source during migration. Which approach meets these requirements?

Accepted Answer

Create a read replica of the source RDS instance, use AWS DMS with CDC from the read replica to Aurora, then promote Aurora.. Creating a read replica of the source RDS for MySQL instance and using AWS DMS with Change Data Capture (CDC) from that replica allows the migration to proceed with minimal downtime. The read replica offloads the CDC overhead from the source, and CDC captures ongoing changes after the full load, enabling a near-zero-downtime cutover. Additionally, the source RDS instance remains fully available for point-in-time recovery (PITR) throughout the migration, as the read replica does not interfere with the source's backup or transaction log retention.

Answer

Use mysqldump to export the database, import into Aurora, and point DNS to Aurora.

Answer

Use AWS DMS with CDC directly from the source RDS instance to Aurora.

Answer

Take a snapshot of the source RDS instance, restore to Aurora, and point DNS to Aurora.

Question 8

A company is migrating an on-premises MongoDB database to Amazon DocumentDB (with MongoDB compatibility). Which AWS service can perform the migration with minimal downtime using ongoing replication?

Accepted Answer

AWS Database Migration Service (AWS DMS). AWS DMS supports MongoDB as a source and Amazon DocumentDB as a target, enabling live migration with ongoing replication via change data capture (CDC). This allows the company to migrate with minimal downtime by continuously applying changes from the source MongoDB to the target DocumentDB until cutover.

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Amazon CloudWatch

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AWS Schema Conversion Tool (AWS SCT)

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AWS Glue

Question 9

A company is migrating a MySQL database to Amazon Aurora MySQL. The database has several stored procedures and triggers. During the migration, some stored procedures fail to execute. What is the most likely cause?

Accepted Answer

The stored procedures use features that are not compatible with Aurora MySQL.. Aurora MySQL is designed to be compatible with MySQL 5.6, 5.7, and 8.0, but it does not support all MySQL features. Stored procedures that rely on deprecated or non-standard MySQL features, such as certain SQL modes, storage engine-specific syntax, or unsupported functions, will fail to execute after migration. This is the most common cause of stored procedure failures during a migration to Aurora MySQL.

Answer

Aurora does not support stored procedures.

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The stored procedures exceed the maximum size limit in Aurora.

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The stored procedures use MyISAM tables, which are not supported by Aurora.

Question 10

A company is migrating a 1 TB SQL Server database to Amazon RDS for SQL Server using backup and restore. The database has high transaction volume. Which backup type should be used to minimize downtime?

Accepted Answer

Perform a full backup, then transaction log backups, and restore the full backup with the last log backup.. A full backup followed by transaction log backups allows point-in-time recovery and minimizes downtime during migration. You restore the full backup to RDS, then apply the latest transaction log backup to capture all changes up to the migration cutover, ensuring data consistency without requiring the database to be offline for the entire duration.

Answer

Perform only transaction log backups and restore them to RDS.

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Perform a differential backup and restore it to RDS.

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Perform a full backup and restore it to RDS.

Question 11

A company is migrating a 100 GB Oracle database to Amazon RDS for Oracle. They want to use AWS DMS. The source database is in a different AWS account. What is required to allow DMS to connect to the source?

Accepted Answer

Establish VPC peering or VPN between the source and target VPCs, and configure security group rules.. AWS DMS requires network connectivity between the replication instance and the source database. Since the source is in a different AWS account, VPC peering or a VPN connection must be established to route traffic between the VPCs. Additionally, security group rules in both VPCs must allow inbound/outbound traffic on the Oracle listener port (default 1521) from the DMS replication instance's IP or security group.

Answer

Assign an IAM role to the source database to allow DMS access.

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Configure an S3 VPC gateway endpoint for the source VPC.

Answer

Create a VPC endpoint for DMS in the source account.

Question 12

A database administrator notices that an Amazon Aurora MySQL DB cluster's primary instance is experiencing high CPU utilization due to a long-running analytical query. The application can tolerate eventual consistency. What is the MOST cost-effective solution to reduce CPU load on the primary instance?

Accepted Answer

Configure an Auto Scaling policy for Aurora Replicas and modify the application to use the reader endpoint.. Offloading read queries to Aurora Replicas is cost-effective and reduces primary load without additional infrastructure.

Answer

Create a read replica in a different region and route read traffic there.

Answer

Increase the instance size of the primary instance.

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Enable Aurora Parallel Query on the cluster.

Question 13

A company is deploying a new DynamoDB table for a global application. The table must have low latency reads and writes across multiple AWS regions. Which configuration should be used?

Accepted Answer

Use DynamoDB global tables with replicate streams.. DynamoDB global tables provide a fully managed, multi-region, multi-master solution that automatically replicates data across selected AWS Regions, enabling low-latency reads and writes globally. By enabling DynamoDB Streams on the table, global tables use the streams to capture item-level changes and replicate them to other regions, ensuring eventual consistency and high availability for global applications.

Answer

Enable DynamoDB Accelerator (DAX) in each region.

Answer

Use DynamoDB Accelerator (DAX) with cross-region replication.

Answer

Create a single table in the primary region and use Amazon CloudFront for reads.

Question 14

An Amazon RDS for MySQL DB instance has a high number of connections and the application is experiencing slow response times. The database administrator wants to identify the queries that are causing the most load. Which approach is most effective?

Accepted Answer

Enable Amazon RDS Performance Insights and review the top SQL queries. Performance Insights provides a dashboard to identify top queries by load. Option A is wrong because it shows connections, not query performance. Option B is wrong because CloudWatch logs show slow queries but not in real-time. Option D is wrong because RDS events show instance events, not query load.

Answer

Enable slow query logs and analyze them in CloudWatch Logs

Answer

Monitor the DatabaseConnections metric in CloudWatch

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Check RDS events for any error messages

Question 15

A company wants to ensure that their Amazon RDS for PostgreSQL database is automatically backed up every day and retains backups for 30 days. Which configuration should they use?

Accepted Answer

Enable automated backups with a retention period of 30 days.. Automated backups are enabled by default with a retention period of 1-35 days. Setting backup retention period to 30 days meets the requirement.

Answer

Set the backup retention period to 0 to disable automated backups and use manual snapshots.

Answer

Create a manual snapshot daily using AWS Backup.

Answer

Enable Multi-AZ deployment for automatic failover.

Question 16

A company is running an Amazon DynamoDB table with on-demand capacity mode. The table experiences occasional throttling during peak hours. The application team wants to understand the read/write patterns to optimize the table design. Which approach should the database specialist take to analyze the throttling events?

Accepted Answer

Enable CloudWatch Contributor Insights for DynamoDB to identify throttled requests.. CloudWatch Contributor Insights analyzes high-cardinality attributes and provides detailed information about throttling requests, such as which items or partitions are causing throttling.

Answer

Enable DynamoDB Accelerator (DAX) to cache reads and reduce throttling.

Answer

Use AWS CloudTrail to log all DynamoDB API calls and analyze the logs.

Answer

Switch to provisioned capacity mode with auto scaling to handle the spikes.

Question 17

A company is experiencing increased latency on their RDS for PostgreSQL instance. The CloudWatch metrics show high ReadIOPS but low CPU utilization. Which action is MOST likely to resolve the issue?

Accepted Answer

Increase the instance size or switch to a gp3 volume. High ReadIOPS with low CPU indicates an I/O bottleneck. Increasing the instance size provides more dedicated IOPS, and switching to gp3 volume offers better baseline performance and throughput compared to gp2. Option A is incorrect because migrating to Aurora does not directly address the I/O bottleneck and involves additional considerations. Option C is incorrect because Multi-AZ provides high availability, not improved performance. Option D is incorrect because storage auto-scaling only increases storage capacity, not IOPS or throughput.

Answer

Migrate the database to Amazon Aurora PostgreSQL

Answer

Enable Multi-AZ deployment

Answer

Enable storage auto-scaling

Question 18

A company is migrating a 10 TB MongoDB database to Amazon DocumentDB. The migration must have minimal downtime. Which strategy should be used?

Accepted Answer

Use AWS DMS with MongoDB as source and DocumentDB as target, with change data capture.. AWS DMS with MongoDB as source and DocumentDB as target, using change data capture (CDC), is the correct strategy because it enables a live migration with minimal downtime. DMS performs an initial full load of the 10 TB database and then continuously replicates ongoing changes from the MongoDB oplog, allowing you to cut over to DocumentDB with only a brief pause.

Answer

Use mongodump to export the database and mongorestore to import into DocumentDB.

Answer

Use AWS CloudEndure to replicate the MongoDB server to DocumentDB.

Answer

Copy the database files to Amazon S3 and restore to DocumentDB.

Question 19

A company is experiencing increased latency on their Amazon RDS for PostgreSQL instance. The application team reports that queries are taking longer than usual. The database metrics show high CPU utilization and a spike in write operations. Which initial step should the database specialist take to diagnose the issue?

Accepted Answer

Enable Performance Insights on the DB instance to analyze the workload.. Enabling Performance Insights provides a detailed performance analysis and helps identify the root cause of the latency. It is the recommended first step for diagnosing database performance issues.

Answer

Create a read replica to offload read traffic from the primary instance.

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Modify the DB instance to a larger instance class to handle the load.

Answer

Enable enhanced monitoring to get OS-level metrics of the DB instance.

Question 20

A company is migrating an on-premises PostgreSQL database to Amazon RDS for PostgreSQL. The database is 2 TB in size and has a sustained write rate of 50 MB/s. The migration must have minimal downtime. Which migration approach should be used?

Accepted Answer

Use AWS DMS with ongoing replication (change data capture). AWS DMS with ongoing replication (change data capture) is the correct approach because it allows a full load of the 2 TB database followed by continuous replication of changes from the on-premises PostgreSQL source to the RDS for PostgreSQL target, minimizing downtime to a brief cutover window. The sustained 50 MB/s write rate indicates a high-volume transactional workload that cannot be captured by a single full-load task, making CDC essential for near-zero downtime migration.

Answer

Create an RDS read replica from the on-premises database

Answer

Use pg_dump and pg_restore

Answer

Use AWS DMS with a full-load task only