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Monitor High CPU Usage In SQL Server With Extended Events

11 min read 11-14- 2024
Monitor High CPU Usage In SQL Server With Extended Events

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Monitoring high CPU usage in SQL Server is crucial for maintaining optimal database performance and ensuring the efficient execution of queries. When your SQL Server experiences spikes in CPU usage, it can slow down the entire system, affecting the performance of applications that depend on it. One effective way to monitor CPU usage is through SQL Server’s Extended Events feature. In this post, we will delve into how to effectively use Extended Events to identify and address CPU usage issues, providing you with a comprehensive guide that includes practical examples, tips, and a detailed breakdown of the process.

Understanding High CPU Usage in SQL Server

Why CPU Usage Matters

CPU usage is a critical metric for database performance. High CPU usage can indicate inefficient queries, missing indexes, or even poorly designed database schemas. Monitoring CPU performance helps in diagnosing issues before they escalate into major performance bottlenecks. When CPU utilization exceeds acceptable thresholds, it can lead to slow response times and decreased application availability.

What are Extended Events?

Extended Events is a lightweight performance monitoring system that allows you to collect detailed information about the SQL Server instance and the events that occur within it. It is more efficient than the older SQL Profiler and can be used to track various performance metrics, including CPU usage.

Setting Up Extended Events for CPU Monitoring

Creating an Extended Events Session

To monitor CPU usage, you will need to create an Extended Events session. Here’s a step-by-step guide on how to do this:

  1. Open SQL Server Management Studio (SSMS): Launch SSMS and connect to your SQL Server instance.
  2. Navigate to the Extended Events Node: In the Object Explorer, expand the "Management" node, then right-click on "Extended Events" and select "New Session Wizard".
  3. Name Your Session: Provide a meaningful name for your session, such as MonitorHighCPUUsage.
  4. Select Events: In this section, you can specify which events to capture. For monitoring CPU, consider selecting the following events:
    • sql_batch_completed
    • rpc_completed
    • sql_statement_completed
    • sql_server.sql_statement.sql_batch_completed

Here’s a quick table of the events:

<table> <tr> <th>Event Name</th> <th>Description</th> </tr> <tr> <td>sql_batch_completed</td> <td>Fires when a SQL batch has completed execution.</td> </tr> <tr> <td>rpc_completed</td> <td>Fires when a Remote Procedure Call (RPC) has completed.</td> </tr> <tr> <td>sql_statement_completed</td> <td>Fires when a T-SQL statement completes execution.</td> </tr> </table>

  1. Add Filters: Filters can help you capture only the relevant data. You can filter based on CPU time, duration, or other parameters to focus on high CPU usage events.

  2. Set Data Storage Options: Choose where you want to store the collected data (i.e., in a ring buffer, to a file, or in a SQL table). Storing data in a file can be helpful for long-term analysis.

  3. Review and Create: Once you've configured the session, review the settings and click “Finish” to create the session.

Starting the Extended Events Session

To start monitoring, right-click on the session you created and select "Start Session". This will begin capturing the specified events in real-time.

Analyzing Captured Data

Accessing Collected Data

After your session runs for a period of time, you can analyze the collected data. To do this:

  1. Right-click on the session in the Extended Events node.
  2. Select "Watch Live Data" or "View Target Data" based on your storage option.
  3. Review the Events: Examine the captured events for patterns of high CPU usage.

Important Metrics to Monitor

When analyzing the data, keep an eye on the following metrics:

  • CPU Time: This tells you how much CPU time each event has consumed.
  • Execution Count: The number of times a particular query was executed.
  • Duration: How long the query took to execute, which can help identify slow-performing queries.

Sample Query to Identify High CPU Queries

You can also run queries against the collected event data to find the top queries contributing to CPU usage:

SELECT
    event_data.value('(data[@name="cpu_time"]/value)[1]', 'int') AS CpuTime,
    event_data.value('(data[@name="duration"]/value)[1]', 'int') AS Duration,
    event_data.value('(data[@name="statement"]/value)[1]', 'nvarchar(max)') AS SQLStatement,
    COUNT(*) AS ExecutionCount
FROM 
    sys.fn_xe_file_target_read_file('path_to_your_file*.xel', null, null, null) AS event_data
WHERE 
    event_data.value('(data[@name="cpu_time"]/value)[1]', 'int') > 1000  -- Threshold for high CPU usage
GROUP BY 
    event_data.value('(data[@name="cpu_time"]/value)[1]', 'int'),
    event_data.value('(data[@name="duration"]/value)[1]', 'int'),
    event_data.value('(data[@name="statement"]/value)[1]', 'nvarchar(max)')
ORDER BY 
    CpuTime DESC;

This query retrieves the CPU time, duration, and the SQL statements that consumed excessive CPU, allowing you to focus on optimization efforts.

Troubleshooting High CPU Usage

Identifying Problematic Queries

After capturing and analyzing the data, you may identify certain queries that consistently consume high CPU. To address this, consider:

  • Query Optimization: Modify the queries to improve performance. This may involve rewriting the query, adjusting joins, or changing the way data is accessed.
  • Index Management: Ensure that appropriate indexes are in place. Missing indexes can lead to increased CPU usage as SQL Server performs full table scans.
  • Statistics Update: Outdated statistics can lead to poor execution plans. Regularly update statistics on large tables to help the optimizer make informed decisions.

Important Note

"Remember to always test changes in a development environment before applying them to production. This helps prevent unexpected downtime or issues."

Resource Consumption Patterns

Monitor overall resource consumption patterns over time. Consider using SQL Server’s built-in tools like Activity Monitor or Performance Monitor to correlate CPU usage with other system metrics, such as disk I/O or memory usage.

Best Practices for Extended Events

  1. Limit Data Collection: Avoid collecting too much data to ensure that your monitoring does not itself become a performance issue.
  2. Regularly Review Sessions: Periodically review your Extended Events sessions and adjust them based on new insights or changes in your environment.
  3. Use Alerts: Set up SQL Server alerts to notify you when CPU usage exceeds certain thresholds, allowing for proactive intervention.

Conclusion

Monitoring high CPU usage in SQL Server using Extended Events is an effective approach to maintaining optimal performance. By setting up appropriate sessions, capturing critical data, and analyzing the results, you can identify and resolve issues before they become severe problems. Regular monitoring and proactive adjustments will not only keep your SQL Server running smoothly but also enhance the overall experience for users and applications reliant on your database.

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