DBS-C01 Monitoring and Troubleshooting Practice Test 18 — 15 Questions

Question 1

A DevOps engineer notices that an Amazon DynamoDB table's read capacity is frequently throttled during peak hours. The table has read-once, read-many workload. Which action is MOST cost-effective to reduce throttling?

Accepted Answer

Enable DynamoDB Accelerator (DAX). Option B is correct because DynamoDB Accelerator (DAX) caches reads, reducing read capacity consumption. Option A is wrong because increasing read capacity costs more. Option C is wrong because auto-scaling still incurs cost. Option D is wrong because changing to On-Demand may be more expensive for predictable workloads.

Answer

Enable auto-scaling for read capacity

Answer

Switch to On-Demand capacity mode

Answer

Increase the provisioned read capacity units

Question 2

A database specialist is troubleshooting an Amazon Aurora MySQL cluster. The writer instance's CPU is at 90% and there are frequent 'Lock wait timeout exceeded' errors. The application uses many short-lived connections. What should the specialist do FIRST to reduce lock contention?

Accepted Answer

Enable RDS Proxy to pool database connections. Option A is correct because enabling RDS Proxy reduces connection churn and pools connections, reducing lock contention. Option B is wrong because increasing instance size adds CPU but doesn't directly address lock contention. Option C is wrong because reducing connections may increase contention per connection. Option D is wrong because read replicas don't handle write locks.

Answer

Add additional read replicas to distribute read traffic

Answer

Increase the instance size to handle more concurrent transactions

Answer

Reduce the maximum number of connections in the application

Question 3

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. The migration uses AWS DMS. After the migration, the database has a 30-minute recovery point objective (RPO). Which Amazon RDS feature should be configured to meet a 5-minute RPO?

Accepted Answer

Enable automated backups with a retention period of 7 days. Option C is correct because automated backups with point-in-time recovery enable recovery to any point within the retention period, meeting 5-minute RPO. Option A is wrong because Multi-AZ is for high availability, not backup. Option B is wrong because read replicas don't provide backup. Option D is wrong because manual snapshots are taken on-demand, not continuously.

Answer

Enable Multi-AZ deployment

Answer

Take manual snapshots every 5 minutes

Answer

Create a read replica in another region

Question 4

A developer reports that an Amazon ElastiCache for Redis cluster's memory usage is consistently above 90%. The application uses Redis for caching and session storage. Which configuration change would MOST effectively reduce memory pressure?

Accepted Answer

Enable eviction with volatile-LRU policy. Option B is correct because enabling eviction with a volatile-LRU policy frees memory by removing expired keys. Option A is wrong because scaling up increases memory but costs more. Option C is wrong because persistence writes to disk, not memory. Option D is wrong because disabling replication does not reduce memory usage.

Answer

Scale up to a larger node type

Answer

Enable AOF persistence to free memory

Answer

Disable replication to reduce memory overhead

Question 5

A database specialist is monitoring an Amazon DynamoDB global table with two replicas in separate regions. The specialist notices that the 'ReplicatedWriteConflictCount' metric is increasing. What is the MOST likely cause?

Accepted Answer

The same item is being written concurrently in multiple regions. Option D is correct because concurrent writes to the same item in different regions cause conflicts. Option A is wrong because provisioned throughput affects throttling, not conflicts. Option B is wrong because network latency does not cause conflicts. Option C is wrong because eventual consistency does not cause conflicts.

Answer

Insufficient write capacity in one of the regions

Answer

High network latency between the regions

Answer

The application is using strongly consistent reads

Question 6

A company uses Amazon RDS for PostgreSQL with logical replication to a downstream system. The replication slot grows unbounded and causes storage full issues. Which action resolves this without data loss?

Accepted Answer

Monitor the replication slot and advance it using pg_replication_slot_advance. Option C is correct because monitoring and advancing the replication slot prevents WAL accumulation. Option A is wrong because disabling replication causes data loss. Option B is wrong because increasing storage is a temporary fix, not a resolution. Option D is wrong because deleting old WAL logs may break replication.

Answer

Disable logical replication and use DMS instead

Answer

Increase the allocated storage size of the RDS instance

Answer

Delete the replication slot and recreate it

Question 7

A developer is troubleshooting slow queries in Amazon RDS for MySQL. The 'Threads_running' status variable is consistently above 200. The application uses connection pooling. Which metric should be monitored to identify the root cause?

Accepted Answer

Innodb_row_lock_current_waits. Option A is correct because high 'Threads_running' often indicates queries waiting on locks or I/O. Option B is wrong because 'Connections' shows total connections, not concurrent active queries. Option C is wrong because 'Queries' shows total queries over time, not concurrency. Option D is wrong because 'Slow_queries' shows only long-running queries.

Answer

Queries_per_second

Answer

Slow_queries

Answer

Threads_connected

Question 8

A company uses Amazon Redshift for data warehousing. A nightly ETL job fails with 'Disk full' error on some nodes. The cluster has 8 dc2.large nodes. Which action will MOST efficiently resolve the issue without increasing costs?

Accepted Answer

Run a VACUUM command to reclaim space. Option B is correct because VACUUM reclaims space from deleted rows without adding cost. Option A is wrong because adding nodes increases cost. Option C is wrong because increasing slice count is not possible without changing node type. Option D is wrong because compression reduces storage but may not immediately free space.

Answer

Increase the number of slices per node

Answer

Add more nodes to the cluster

Answer

Enable compression on all tables

Question 9

A database specialist is troubleshooting an Amazon RDS for SQL Server instance that is experiencing high CPU utilization. The instance has multiple databases. Which TWO actions should the specialist take to identify the cause?

Accepted Answer

Use Performance Insights to identify top SQL queries. Options B and D are correct because they directly identify top CPU queries and resource-intensive databases. Option A is wrong because increasing CPU doesn't diagnose. Option C is wrong because read replicas don't help with CPU. Option E is wrong because instance class change is a fix, not diagnosis.

Answer

Create a read replica to offload read traffic

Answer

Increase the instance size to handle the load

Answer

Modify the DB instance class to a burstable type

Question 10

An Amazon DynamoDB table is experiencing throttled write requests. The table uses provisioned capacity with auto-scaling enabled. Which THREE factors could contribute to throttling despite auto-scaling?

Accepted Answer

Auto-scaling maximum capacity is set too low. Options A, B, and D are correct. Auto-scaling cannot handle sudden bursts (A), hot partitions (B), or exceeded max capacity (D). Option C is wrong because eventual consistency doesn't cause throttling. Option E is wrong because GSI consumes write capacity from the table.

Answer

Global secondary index is defined with same partition key

Answer

Use of eventually consistent reads

Question 11

A company uses Amazon RDS for PostgreSQL with Multi-AZ. The primary instance fails and a failover occurs. After failover, the application reports elevated write latency. Which TWO are possible causes?

Accepted Answer

The buffer pool is not warm on the new primary. After a Multi-AZ failover, the new primary instance starts with a cold buffer pool (no cached data blocks). PostgreSQL relies on shared buffers to cache frequently accessed data; without a warm cache, every read request must fetch data from disk, which increases I/O and write latency because writes often require reading the affected pages first. This is a known behavior in RDS for PostgreSQL after failover, and it resolves as the buffer pool warms up over time.

Answer

A read replica is now promoting to primary

Answer

The new primary has a smaller instance size

Answer

Automated backups are running on the new primary

Question 12

A company is running a production Amazon RDS for PostgreSQL database. The database has experienced a sudden spike in CPU utilization, causing application timeouts. The monitoring team needs to identify the root cause. Which AWS service or feature should be used to analyze the database load and identify the specific queries causing the high CPU?

Accepted Answer

Amazon RDS Performance Insights. Option D is correct because Performance Insights provides a database performance tuning and monitoring feature that helps you quickly assess the load on your database and determine when and where to take action. Option A is wrong because CloudWatch Logs captures database logs, not real-time performance data. Option B is wrong because Enhanced Monitoring provides OS-level metrics, not database query details. Option C is wrong because AWS Trusted Advisor provides best practice checks but not query-level analysis.

Answer

Enhanced Monitoring

Answer

Amazon CloudWatch Logs

Answer

AWS Trusted Advisor

Question 13

A company is using Amazon DynamoDB for a high-traffic application. The application is experiencing intermittent `ProvisionedThroughputExceededException` errors. The team has already increased the read and write capacity units multiple times but the errors persist. Which of the following is the MOST likely cause of the issue?

Accepted Answer

A hot key or uneven partition access pattern is causing throttling. Option B is correct because hot keys or uneven access patterns can cause throttling even if overall provisioned capacity appears sufficient. Option A is wrong because increasing capacity units should reduce throttling if the issue is simply capacity. Option C is wrong because Global Tables replication does not cause throttling on the source table. Option D is wrong because DynamoDB Accelerator (DAX) reduces read load on the table, not write, and improper use might cause cache misses but not ProvisionedThroughputExceededException.

Answer

DynamoDB Accelerator (DAX) is not properly configured

Answer

The table is part of a DynamoDB Global Table and replication is causing conflicts

Answer

The provisioned capacity is not increased enough

Question 14

A database administrator notices that an Amazon RDS for MySQL instance's storage is filling up unexpectedly. The administrator has enabled automated backups and retains them for 7 days. Which of the following actions would help reduce storage consumption without losing the ability to perform point-in-time recovery?

Accepted Answer

Reduce the backup retention period to 1 day. Option B is correct because deleting old automated backups reduces storage used by backup data. Option A is wrong because manual snapshots are separate and do not affect automated backup storage. Option C is wrong because disabling backups would remove point-in-time recovery capability. Option D is wrong because modifying DB instance class does not reduce storage consumption.

Answer

Modify the DB instance to a smaller instance class

Answer

Delete manual DB snapshots

Answer

Disable automated backups

Question 15

A company is using Amazon Redshift for data warehousing. The operations team notices that queries are running slower than usual. Which Amazon Redshift system view should be used to identify the queries that are consuming the most resources?

Accepted Answer

STL_QUERY. Option A is correct because STL_QUERY contains query execution details including resource consumption. Option B is wrong because STV_TBL_PERM shows table permissions, not query performance. Option C is wrong because PG_TABLE_DEF shows table definitions. Option D is wrong because SVV_VACUUM_PROGRESS shows vacuum progress, not query performance.

Answer

SVV_VACUUM_PROGRESS

Answer

PG_TABLE_DEF

Answer

STV_TBL_PERM