DBS-C01 Practice Exam 65 — 20 Questions

Question 1

A company is running a critical Oracle database on Amazon RDS. The DBA wants to set up monitoring to detect if the database is experiencing a high number of full table scans, which may indicate missing indexes. Which TWO metrics should the DBA monitor? (Choose TWO.)

Accepted Answer

TableScanRows. Options B and D are correct. FullTableScans (B) directly counts full scan operations. TableScanRows (D) indicates the number of rows read via full scans. Option A is wrong because BufferCacheHitRatio indicates cache efficiency, not full scans. Option C is wrong because UserCommits shows transaction commits. Option E is wrong because RedoLogSpaceUsage relates to write-ahead logging.

Answer

BufferCacheHitRatio

Answer

UserCommits

Answer

RedoLogSpaceUsage

Question 2

A company uses Amazon Aurora MySQL. They notice that the DB cluster's failover took longer than expected during a recent primary instance failure. CloudWatch shows Failover latency of 120 seconds. Which configuration change would most likely reduce the failover time?

Accepted Answer

Configure the application to use the cluster endpoint with Aurora JDBC driver's fast failover feature.. Option A is correct because Aurora's fast failover requires the JDBC driver to use the cluster endpoint with the Aurora hostlist provider. Option B is wrong because increasing instance size does not reduce failover time. Option C is wrong because Multi-AZ is already inherent in Aurora. Option D is wrong because increasing backup retention does not affect failover.

Answer

Increase the instance class of the primary and replica instances.

Answer

Increase the backup retention period to 35 days.

Answer

Enable Multi-AZ on the DB cluster.

Question 3

A company runs a document database using Amazon DocumentDB. They notice that some queries are taking much longer than expected. The explain plan shows a COLLSCAN. Which action would most improve query performance?

Accepted Answer

Create appropriate indexes on the fields used in query filters. Option A is correct because creating an index on the queried fields avoids collection scans. Option B is wrong because increasing instance size helps but doesn't address the root cause. Option C is wrong because changing consistency level affects read freshness, not performance. Option D is wrong because increasing storage doesn't improve query speed.

Answer

Increase the instance size to the next tier

Answer

Change the read consistency from eventual to strong

Answer

Increase the storage allocated to the instance

Question 4

A company is migrating an on-premises Oracle database to Amazon RDS for Oracle. After migration, the application team reports that queries are slower than before. Which metric in CloudWatch should the DBA review first to check if the instance is resource-constrained?

Accepted Answer

CPUUtilization. Option A is correct because CPUUtilization is a primary indicator of resource saturation. Option B is wrong because DatabaseConnections shows concurrent connections, not resource usage. Option C is wrong because FreeableMemory is important but CPU is more likely the first bottleneck. Option D is wrong because SwapUsage is relevant but not the first metric to check.

Answer

SwapUsage

Answer

FreeableMemory

Answer

DatabaseConnections

Question 5

A data analytics company runs Amazon Redshift clusters. A user reports that a complex query is taking much longer than expected. The DBA uses the STL_QUERY view to check the query execution. Which column in STL_QUERY should the DBA examine to identify if the query is waiting for resources?

Accepted Answer

service_class. Option B is correct because the 'service_class' column indicates the workload management (WLM) queue, which can show if the query is queued. Option A is wrong because 'query' is just the query ID. Option C is wrong because 'starttime' shows when the query started. Option D is wrong because 'aborted' indicates if the query was canceled, not waiting.

Answer

aborted

Answer

query

Answer

starttime

Question 6

A company is running a production Amazon Aurora MySQL-Compatible Edition database. The database has recently experienced several failovers due to replica lag. The DBA needs to implement monitoring to detect replica lag early. Which THREE metrics should be monitored to assess replication health? (Select THREE.)

Accepted Answer

DatabaseConnections. Option A: AuroraReplicaLag is the direct metric for replica lag. Option B: ReplicaLag is the standard metric for MySQL replication lag. Option D: DatabaseConnections can indirectly indicate issues if application retries increase. Option C: BufferCacheHitRatio is about cache efficiency, not replication. Option E: ActiveTransactions is about transactions, not replication.

Answer

ActiveTransactions

Answer

BufferCacheHitRatio

Question 7

A company is migrating their on-premises Oracle database to Amazon RDS for Oracle. They need to ensure minimal downtime. During the migration, they observe that the change data capture (CDC) is falling behind. What is the most effective approach to catch up?

Accepted Answer

Increase the instance size of the target RDS instance. Option B is correct because increasing the instance size provides more resources for replication. Option A is wrong because pausing replication would increase lag. Option C is wrong because switching to full load would cause downtime. Option D is wrong because disabling logging would break CDC.

Answer

Disable supplemental logging on the source

Answer

Pause the CDC task and resume later

Answer

Stop the CDC and perform a full load migration

Question 8

A team is troubleshooting an Amazon Aurora MySQL cluster where the writer instance fails over unexpectedly every few days. The failover is not triggered by manual intervention or maintenance events. CloudWatch metrics show that the failover occurs when the replica lag on the reader instances spikes to over 10 seconds. What is the MOST likely cause of the failover?

Accepted Answer

The reader instances are under-provisioned and cannot keep up with the write rate from the writer. Option D is correct because if the reader instances are overloaded, they may not be able to apply changes quickly enough, causing replica lag. The failover could be due to the failover priority settings or a health check failure. Option A is incorrect because storage issues would affect both writer and readers. Option B is incorrect because an oversized instance would reduce lag, not increase it. Option C is incorrect because long-running queries on the writer would not directly cause replica lag on readers.

Answer

The reader instances are over-provisioned, causing them to become idle and drop connections

Answer

The Aurora cluster is experiencing a storage subsystem bottleneck in a single Availability Zone

Answer

The writer instance is running a long-running transaction that blocks replication

Question 9

A company is using Amazon DynamoDB with auto scaling for read and write capacity. During a traffic spike, write requests are being throttled even though the table's write capacity is below the maximum limit. Which TWO actions should the team take to resolve the throttling?

Accepted Answer

Review the table's partition key design to ensure even distribution of write traffic. Option A is correct because auto scaling may have a lag in provisioning capacity; pre-warming can help. Option C is correct because a hot partition can cause throttling even if overall capacity is not exhausted. Option B is incorrect because write sharding is not a built-in DynamoDB feature. Option D is incorrect because global tables add complexity and are not a direct fix for throttling. Option E is incorrect because decreasing read capacity does not help writes.

Answer

Enable DynamoDB Streams on the table to offload writes to a Lambda function

Answer

Create a DynamoDB global table to distribute writes across regions

Answer

Decrease the read capacity to free up resources for writes

Question 10

A company uses Amazon DynamoDB with auto scaling enabled. During a sales event, the write capacity consumption increases, but the table does not scale up as expected, resulting in throttled requests. The table has read/write capacity mode set to 'Provisioned' with auto scaling configured. What should the team check first to troubleshoot the issue?

Accepted Answer

Check the target utilization percentage in the auto scaling policy. Option B is correct because auto scaling uses a target utilization percentage; if it's set too high, it may not trigger scaling soon enough. Option A is incorrect because auto scaling controls the provisioned capacity, not the table class. Option C is incorrect because auto scaling does not require manual approval. Option D is incorrect because auto scaling can increase capacity up to the maximum limit, regardless of the GSI.

Answer

Verify that the auto scaling role has the necessary IAM permissions

Answer

Check whether the table class is DynamoDB Standard-IA

Answer

Check if a global secondary index (GSI) has its own write capacity that is throttling

Question 11

A company is using Amazon Redshift for analytics. The database administrator notices that some queries are slow and the system is running out of memory. Which THREE steps should the administrator take to improve performance?

Accepted Answer

Optimize the table design by choosing appropriate distkeys and sortkeys. Option A is correct because adding nodes increases memory. Option B is correct because distkey and sortkey optimization reduces data movement. Option C is correct because WLM queues can limit concurrency to reduce memory contention. Option D is incorrect because vacuum is for disk space, not memory. Option E is incorrect because increasing node count (scale out) is better than scale up for memory.

Answer

Increase the node size (scale up) to get more memory per node

Answer

Run the VACUUM command to reclaim space from deleted rows

Question 12

A company uses Amazon DynamoDB as a session store for a web application. The application uses a TTL attribute to expire old sessions. The company noticed that expired sessions are not being deleted promptly, causing the table size to grow and increasing costs. The TTL attribute is defined as 'expire_time' with a Unix epoch timestamp. The database specialist verified that TTL is enabled. What should the specialist do to ensure expired sessions are deleted in a timely manner?

Accepted Answer

Increase the provisioned write capacity on the table to allow TTL to delete items faster.. Option C is correct because TTL deletion can be delayed if the table has a high write rate; increasing provisioned write capacity can speed up the deletion process. Option A is wrong because DynamoDB does not have a 'ttl_deletion_lag' parameter. Option B is wrong because TTL handles deletion automatically; a Lambda function is unnecessary. Option D is wrong because the attribute type is correct (Number).

Answer

Change the TTL attribute type to String format.

Answer

Configure the 'ttl_deletion_lag' parameter to a lower value.

Answer

Create an AWS Lambda function that scans the table and deletes expired items.

Question 13

A developer is troubleshooting a slow query on Amazon RDS for MySQL. The query joins three large tables and runs frequently. What is the most effective way to identify the bottleneck?

Accepted Answer

Enable the slow query log and analyze the output. Option B is correct because enabling slow query log captures queries that exceed a threshold, allowing analysis. Option A is wrong because Enhanced Monitoring shows OS metrics, not query details. Option C is wrong because Performance Insights shows wait events and SQL, but slow query log specifically targets slow queries. Option D is wrong because CloudWatch metrics show overall performance, not per-query.

Answer

Check the RDS Events for any maintenance notifications

Answer

Review Amazon CloudWatch CPU and memory metrics

Answer

Use AWS Database Migration Service to migrate to a larger instance

Question 14

A company is using Amazon RDS for MySQL and has enabled Enhanced Monitoring. The database administrator wants to identify the top contributors to disk I/O. Which THREE metrics from Enhanced Monitoring should they examine?

Accepted Answer

DirtyBufferFlushRate. Option A is correct because physical reads cause disk I/O. Option C is correct because write operations generate I/O. Option D is correct because dirty buffer flushes cause writes. Option B is incorrect because logical reads are from memory, not disk. Option E is incorrect because network throughput is not disk I/O.

Answer

NetworkThroughput

Answer

LogicalReads

Question 15

A company is running a self-managed MongoDB cluster on Amazon EC2. The cluster consists of three replica set members in different Availability Zones. The primary node recently experienced a crash, and the cluster failed over to a secondary. However, the new primary is showing significantly higher latency. The operations team wants to ensure that failover is fast and consistent. What should be done to improve the failover reliability?

Accepted Answer

Use Amazon EBS io2 Block Express volumes with provisioned IOPS.. Option C: Using Amazon EBS io2 Block Express volumes with higher IOPS and lower latency can reduce the time for the secondary to catch up. Option A: EBS Multi-Attach is not supported for io2? Actually io2 supports multi-attach but for shared volumes, not typically used for MongoDB. Option B: Using instance store volumes may have higher performance but are ephemeral and data loss is possible. Option D: Snapshots are for backups, not for improving failover performance.

Answer

Use Amazon EBS Multi-Attach to allow all replicas to share the same volume.

Answer

Switch to instance store volumes for better I/O performance.

Answer

Configure EBS snapshots to be taken every 5 minutes.

Question 16

Refer to the exhibit. An IAM policy is attached to a user. The user reports that they cannot delete the production-db database. Which statement best explains the behavior?

Accepted Answer

An explicit Deny statement prevents the deletion of the production-db instance. Option C is correct because an explicit Deny overrides any Allow. The Deny statement specifically denies DeleteDBInstance on that resource. Option A is wrong because the policy allows CreateDBInstance. Option B is wrong because DescribeDBInstances is allowed. Option D is wrong because the Deny is explicitly on the production-db ARN.

Answer

The user needs additional permissions to delete any DB instance

Answer

The user does not have permission to describe DB instances

Answer

The user does not have permission to create a DB instance

Question 17

A company uses Amazon RDS for PostgreSQL with Multi-AZ deployment. The primary instance fails, and a failover occurs. After the failover, the application is still unable to connect to the database endpoint. The database administrator checks the RDS console and sees that the new primary is in 'available' state. What should the administrator do next to diagnose the connectivity issue?

Accepted Answer

Check the DNS resolution of the RDS endpoint from the application server. Option C is correct because the DNS CNAME of the RDS endpoint should have updated to point to the new primary. If the application is using the old IP or a cached DNS entry, it may not connect. Option A is incorrect because security group rules are usually unchanged. Option B is incorrect because the subnet group is not the issue. Option D is incorrect because the primary is already in available state.

Answer

Verify that the security group for the RDS instance allows inbound traffic from the application

Answer

Check if the subnet group for the RDS instance is correctly configured

Answer

Restart the RDS instance to force a new connection

Question 18

A social media company runs a multi-region application on Amazon DynamoDB with global tables. The application is deployed in us-east-1 and eu-west-1. Recently, they enabled DynamoDB Streams on the table to trigger an AWS Lambda function for real-time analytics. The Lambda function runs in us-east-1. After enabling streams, they notice that the Lambda function is triggered multiple times for the same update, and the application's write latency in eu-west-1 has increased. The company has strict latency requirements. A database specialist is asked to resolve the issue. What should the database specialist recommend?

Accepted Answer

Modify the Lambda function to check the 'awsRegion' attribute in the stream record and ignore records from other regions.. Option C is correct because global tables replicate writes across regions, and each write generates a stream record. The Lambda function should filter on the 'awsRegion' attribute in the stream record to avoid processing the same update from different regions. Option A is wrong because disabling streams in eu-west-1 would break the replication. Option B is wrong because using a dedicated stream for each region is not supported. Option D is wrong because increasing Lambda concurrency doesn't prevent duplicate processing.

Answer

Increase the Lambda function's reserved concurrency to handle duplicate events faster.

Answer

Create a separate Lambda function in eu-west-1 and use a local stream.

Answer

Disable DynamoDB Streams on the eu-west-1 replica table.

Question 19

Refer to the exhibit. A DBA sees the above log entries for an Amazon Aurora MySQL cluster. What is the most likely cause?

Accepted Answer

There is underlying storage corruption. Option D is correct because the logs indicate table corruption and page corruption, typically due to underlying storage issues. Option A is wrong because connection issues would show different errors. Option B is wrong because backup restore would not cause corruption. Option C is wrong because replication lag shows different symptoms.

Answer

The reader instance is lagging behind the writer

Answer

The DB instance has run out of connections

Answer

A recent backup restore operation failed

Question 20

A company is using Amazon RDS for SQL Server with native backup and restore. The backup process is failing with an error indicating insufficient disk space for the backup file. The DB instance has 200 GB of allocated storage, and the backup file is 50 GB. What should the database administrator do to resolve this issue?

Accepted Answer

Increase the allocated storage for the RDS instance. Option A is correct because native backups are stored on the instance's attached storage; if the storage is full, backups fail. Increasing allocated storage provides more space. Option B is incorrect because automated backups are stored in S3 and do not use instance storage. Option C is incorrect because the error is about disk space, not permissions. Option D is incorrect because changing storage type does not add space.

Answer

Change the storage type to Provisioned IOPS for better performance

Answer

Grant the rds_backup user additional permissions to write to S3

Answer

Switch to automated backups instead of native backups