DBS-C01 Monitoring and Troubleshooting Practice Test 23 — 15 Questions

Question 1

A company is using Amazon DynamoDB Accelerator (DAX) to improve read performance. Recently, the cache hit ratio has dropped significantly. The application uses strongly consistent reads. What is the most likely cause of the low cache hit ratio?

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

Accepted Answer

The application is using strongly consistent reads, which bypass the DAX cache. DAX does not support strongly consistent reads. When an application issues a strongly consistent read, DAX bypasses the cache and sends the request directly to DynamoDB, resulting in a cache miss. If the application recently switched to or increased strongly consistent reads, the cache hit ratio would drop significantly.

Answer

The DynamoDB table's write capacity is too low

Answer

The DAX cluster has too few nodes

Answer

The DAX cluster's TTL is set too low

Question 2

A database administrator is monitoring an Amazon RDS for SQL Server DB instance and notices that the FreeableMemory metric is consistently below 200 MB. Which of the following actions is most appropriate to mitigate performance issues?

Accepted Answer

Scale up the DB instance to a larger instance class with more memory. A low FreeableMemory metric consistently below 200 MB indicates memory pressure on the RDS for SQL Server DB instance. The most effective mitigation is to scale up to a larger instance class with more memory, directly addressing the resource shortage. Option D is correct because it increases available memory. Option B is incorrect because disabling SQL Server Agent and error logging does not free significant memory and may disrupt essential operations. Option A is incorrect because changing the maintenance window does not affect memory usage. Option C is incorrect because enabling backups with a shorter retention period does not impact memory.

Answer

Modify the DB instance's maintenance window to off-peak hours

Answer

Disable the SQL Server Agent and error logging

Answer

Enable automatic backups with a shorter retention period

Question 3

A company is using Amazon Redshift for data warehousing. The query performance has degraded over time. The DBA suspects that the distribution style of large tables is suboptimal. Which Redshift system view should be queried to identify distribution skew?

Accepted Answer

SVV_DISKUSAGE. SVV_DISKUSAGE provides disk usage per slice, which helps identify distribution skew. Option A is wrong because STL_SCAN provides details about scan operations, not skew. Option B is wrong because PG_TABLE_DEF shows table definitions, not skew. Option D is wrong because STV_TBL_PERM shows storage usage per table but not per slice, making it less suitable for skew analysis.

Answer

STL_SCAN

Answer

PG_TABLE_DEF

Answer

STV_TBL_PERM

Question 4

An application using Amazon DynamoDB is experiencing higher than expected read costs. The table uses on-demand capacity mode. The read pattern is mostly fetching small items (1 KB) using GetItem. Which of the following is the most cost-effective optimization?

Accepted Answer

Switch to eventually consistent reads for GetItem operations. The most cost-effective because eventually consistent reads consume half the read capacity units (0.5 RCU for items up to 4 KB) compared to strongly consistent reads (1 RCU). Since items are small (1 KB) and the table uses on-demand capacity, halving RCU consumption directly reduces read costs. Option A: Switching to provisioned capacity with auto scaling adds complexity and may not reduce costs if traffic is unpredictable; on-demand is already suitable for variable workloads. Option B: Application-level compression would not significantly reduce RCU consumption because items are already under the 4 KB RCU threshold. Option C: Adding DAX introduces additional cost and primarily improves latency, not read cost, as DAX still charges for reads from DynamoDB.

Answer

Change the table to provisioned capacity mode with auto scaling

Answer

Compress the items using application-level compression

Answer

Use DAX to cache the read results

Question 5

Which TWO metrics should be monitored together to detect a memory leak in an Amazon RDS for Oracle DB instance? (Choose TWO.)

Accepted Answer

FreeableMemory. FreeableMemory (A) is correct because it reports the amount of available RAM on the RDS instance; a memory leak in the Oracle SGA/PGA or OS processes causes FreeableMemory to trend steadily downward over time, making it the primary indicator of leaked memory. SwapUsage (B) is correct because as freeable memory is exhausted, the OS begins paging to swap, so rising SwapUsage alongside falling FreeableMemory confirms memory pressure caused by a leak rather than normal cache growth. Monitoring these two together distinguishes a true leak (continuous decline in FreeableMemory with increasing SwapUsage) from transient workload spikes. ReadIOPS (C) reflects disk read activity, DatabaseConnections (D) counts client sessions, and NetworkThroughput (E) measures bytes transferred; none of these directly reveal memory exhaustion or swap paging, so they are not the right pair for detecting a memory leak.

Answer

ReadIOPS

Answer

DatabaseConnections

Answer

NetworkThroughput

Question 6

Which THREE steps should be taken to troubleshoot high replica lag in an Amazon Aurora MySQL DB cluster? (Choose THREE.)

Accepted Answer

Review network latency between the writer and replica. Options A, C, and E are correct. High replica lag in Amazon Aurora MySQL can be caused by network latency (A), resource contention on the replica (C), or issues with the replication process itself (E). Option B (increasing instance size) is a mitigation, not a troubleshooting step—you diagnose first. Option D (disabling binary logging) would break replication entirely.

Answer

Increase the instance size of the replica

Answer

Disable binary logging on the writer

Question 7

Which TWO CloudWatch Logs features can be used to monitor and troubleshoot Amazon RDS for SQL Server error logs? (Choose TWO.)

Accepted Answer

Setting metric filters to count error occurrences. The correct answers are B and E. CloudWatch Logs allows real-time monitoring of log streams (E) and setting metric filters to count specific error occurrences (B). Option A (AWS X-Ray) is for distributed tracing, not log monitoring. Option C (exporting to S3) is for archival, not real-time monitoring. Option D (CloudTrail) captures API activity, not database error logs.

Answer

Integrating with AWS X-Ray for trace analysis

Answer

Exporting logs to Amazon S3

Answer

Using AWS CloudTrail to capture log events

Question 8

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. InnoDB row lock waits directly indicate contention for row-level locks, which is a common cause of high Threads_running when many queries are blocked waiting for locks held by other transactions. Monitoring Innodb_row_lock_current_waits reveals the number of transactions currently waiting for a row lock, pinpointing lock contention as the root cause of slow queries and elevated running threads.

Answer

Queries_per_second

Answer

Slow_queries

Answer

Threads_connected

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. Option B is correct because Amazon RDS Performance Insights collects and visualizes database load by wait event and SQL statement, letting the specialist pinpoint the top SQL queries consuming CPU on the SQL Server instance. Option E is correct because Enhanced Monitoring publishes OS-level metrics (via the RDS monitoring agent) such as CPU utilization broken down by process, load average, and memory, which helps determine whether the high CPU originates from the database engine or other OS processes. Option A is not appropriate because creating a read replica offloads read traffic but does not diagnose the root cause of high CPU on the existing instance. Option C is not appropriate because increasing the instance size only masks the symptom by adding capacity rather than identifying the cause. Option D is not appropriate because switching to a burstable DB instance class changes performance characteristics and does not help diagnose the CPU issue.

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. Auto-scaling can prevent throttling only if the maximum capacity is set appropriately and traffic patterns are predictable. Option B is correct because if the auto-scaling maximum capacity is set too low, the table cannot scale enough to handle the write demand. Option C is correct because auto-scaling reacts to sustained traffic but cannot instantly accommodate a sudden traffic spike that exceeds the maximum capacity. Option E is correct because even with auto-scaling, an uneven partition key distribution can cause a single partition to exceed its throughput capacity, leading to throttling. Option A is incorrect; a global secondary index with the same partition key does not inherently cause throttling on the base table. Option D is incorrect because eventually consistent reads affect read capacity, not write capacity, and do not cause write throttling.

Answer

Global secondary index is defined with same partition key

Answer

Use of eventually consistent reads

Question 11

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. (Amazon RDS Performance Insights) is correct because it provides a database performance tuning and monitoring feature that helps quickly assess the load on your database and identify specific queries causing high CPU utilization. Option A (Enhanced Monitoring) is wrong because it provides OS-level metrics, not database query details. Option B (Amazon CloudWatch Logs) is wrong because it captures database logs, not real-time performance data. Option D (AWS Trusted Advisor) is wrong because it provides best practice checks but not query-level analysis.

Answer

Enhanced Monitoring

Answer

Amazon CloudWatch Logs

Answer

AWS Trusted Advisor

Question 12

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. Hot keys or uneven partition access patterns can cause throttling even if overall provisioned capacity appears sufficient. Option A is wrong because DynamoDB Accelerator (DAX) is an in-memory cache that reduces read load, but it does not directly fix capacity exceeded errors; misconfiguration might cause cache misses but not ProvisionedThroughputExceededException. Option B is wrong because Global Tables replication does not cause throttling on the source table; conflicts are handled by last-writer-wins. Option C is wrong because increasing capacity units multiple times without resolving the underlying access pattern suggests the issue is not simply insufficient capacity.

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 13

A company is running a MongoDB-compatible Amazon DocumentDB cluster. The application team reports that write operations are failing intermittently with a `WriteConcernError` indicating that the write concern could not be satisfied. The cluster has one primary and two replicas. What is the MOST likely cause of this issue?

Accepted Answer

One of the replicas is down or experiencing high replication lag. The WriteConcernError occurs because the write concern requires acknowledgment from a certain number of replicas. With a cluster of one primary and two replicas, if any replica is down or has high replication lag, the write concern requirement cannot be satisfied. Option A is correct because that is the most likely cause. Option B is incorrect because the cluster has enough replicas for majority write concern if all are healthy. Option C is incorrect because read preference does not affect write operations. Option D is incorrect because the primary being overloaded with reads would not cause a WriteConcernError; it would affect performance but not the ability to satisfy write concern.

Answer

The cluster does not have enough replica instances to satisfy the write concern

Answer

The application is using an incorrect read preference

Answer

The primary instance is overloaded with read requests

Question 14

A company is using Amazon ElastiCache for Redis as a caching layer. The application is experiencing higher latency than expected. The team suspects that cache evictions are occurring due to memory pressure. Which ElastiCache metric should be monitored to confirm this?

Accepted Answer

Evictions. The `Evictions` metric in ElastiCache for Redis tracks the number of keys evicted due to memory pressure, which directly indicates cache evictions. Option A is incorrect because `CurrConnections` shows the number of current client connections, not evictions. Option C is incorrect because `ReplicationLag` measures the delay between the primary and replica nodes, not evictions. Option D is incorrect because `CacheHits` shows the number of successful key lookups, not evictions.

Answer

CurrConnections

Answer

ReplicationLag

Answer

CacheHits

Question 15

A company is using Amazon RDS for MySQL and needs to monitor for slow queries. Which TWO AWS services can be used to capture and analyze slow query logs? (Choose TWO.)

Accepted Answer

Amazon RDS Performance Insights. Amazon RDS Performance Insights (B) is correct because it provides a visual, query-level view of database load and can identify the top SQL statements contributing to load, including slow-running queries on RDS for MySQL, without requiring manual log parsing. Amazon CloudWatch Logs (E) is correct because RDS for MySQL can publish the slow query log to CloudWatch Logs, where you can search, filter, and analyze entries using metric filters and Logs Insights queries. Amazon S3 (A) is not a monitoring or log-analysis service; it is object storage and would only hold exported logs, not capture or analyze slow queries directly. AWS Config (C) tracks resource configuration changes and compliance, not database query performance. AWS CloudTrail (D) records AWS API activity and management events, not the SQL statements executed against a MySQL database.

Answer

Amazon S3

Answer

AWS Config

Answer

AWS CloudTrail