SQL Server’s Extended Events: A Detailed Guide to Advanced Diagnostics
Understanding the internals of SQL Server is vital for effectively managing and troubleshooting database systems. One powerful tool within SQL Server’s arsenal for tracking and diagnosing performance concerns and other issues is Extended Events (XEvents). Extended Events is a highly flexible and scalable event handling system that allows administrators and developers alike to collect detailed information related to SQL Server’s operations efficiently. In this detailed guide, we will explore Extended Events, its architecture, how to set it up, and how to use it to perform advanced diagnostics on SQL Server.
Introduction to Extended Events
SQL Server’s Extended Events are an event-driven diagnostic system introduced in SQL Server 2008 that provides the means to collect, analyze, and respond to data relating to SQL Server processes. Replacing the older SQL Trace and SQL Server Profiler tools, Extended Events use minimal performance resources and offer more granularity in terms of event selection and filtering.
Understanding the Components of Extended Events
Extended Events is composed of several key components that work together to provide a full monitoring and diagnostics system:
- Events: These are points within the SQL Server code that can trigger the gathering of diagnostic data.
- Event Sessions: A package of events collected together with specifications on how they should be collected and for how long.
- Targets: These define the storage locations and structures for the event data collected.
- Predicates: Offering a form of filtering, predicates limit which events get collected based on criteria specified by the user.
- Actions: Additional data elements that can be collected with event data, often used for additional inspection or correlation purposes.
All of these components are configurable and enable the implementation of a precise and optimized monitoring framework within SQL Server environments.
Setting Up Extended Events
Setting up Extended Events begins with the creation of an event session. This process includes selecting the events, specifying predicates for filtering, determining the targets, and defining any additional actions.
Creating an Event Session
Event sessions can be created using SQL Server Management Studio (SSMS) or via T-SQL commands. The GUI in SSMS provides a user-friendly method for creating and managing sessions. Alternatively, T-SQL can be used for scripting the creation of sessions, which is particularly useful in automating setups or deploying to multiple servers.
Event Sessions via SQL Server Management Studio (SSMS)
To create an Extended Events session within SSMS:
- Connect to the database server instance in SSMS.
- Navigate to the ‘Management’ folder in Object Explorer, and then to ‘Extended Events’.
- Right-click the ‘Sessions’ folder and choose ‘New Session Wizard’ which will guide through the creation of a new session.
The wizard will ask for the necessary details such as the name of the session, the events to monitor, predicates for filtering, and targets for data collection.
Event Sessions via T-SQL
CREATE EVENT SESSION [MySession] ON SERVER
ADD EVENT sqlserver.sql_statement_completed
(ACTION (sqlserver.sql_text, sqlserver.database_id)
WHERE (sqlserver.database_id = 5))
ADD TARGET package0.event_file
(SET filename=N'MySessionOutput')
WITH (MAX_MEMORY = 4096 KB, EVENT_RETENTION_MODE = ALLOW_SINGLE_EVENT_LOSS, MAX_DISPATCH_LATENCY = 30 SECONDS)
GO
The T-SQL above demonstrates how to create a new event session called ‘MySession’ that captures when SQL statements are completed for a database with an ID of 5, saving the output to a file named ‘MySessionOutput’.
Managing and Viewing Extended Events Data
Once the Extended Events session is active, event data gets captured as specified in the configurations. To manage and view the captured data, users can utilize SQL Server Management Studio or the T-SQL language.
Using SQL Server Management Studio (SSMS)
Within SSMS:
- Navigate to the Extended Events sessions list.
- Right-click on the session and select ‘Watch Live Data’ to view events as they occur in real-time.
- Select ‘View Target Data’ to see the data that has been collected.
The ‘Live Data’ view is valuable for understanding immediate system behavior, while the ‘Target Data’ view helps investigate past events.
Querying Extended Events Data Using T-SQL
-- Query the file target for recorded events
SELECT event_data = CONVERT(xml, event_data)
FROM sys.fn_xe_file_target_read_file('MySession*.xel', NULL, NULL, NULL)
The T-SQL query above reads from a file target of an Extended Events session, converting the binary data into XML format for easier querying and analysis.
Advanced Diagnostics with Extended Events
Extended Events can be used to perform sophisticated diagnostics on a SQL Server instance. The tool enables deep dives into SQL Server’s operational data, which can be invaluable for performance tuning and identifying root causes of complex problems.
Setting Up Advanced Event Sessions
For advanced diagnostics, consider creating custom event sessions by combining various events, actions, and targets. Doing so can shed light on intricate performance and behavioral intricacies within SQL Server. This often involves incorporating performance-related events, lock events, and I/O-related events into the monitoring process.
Creating an advanced troubleshooting session requires understanding which events are related to the symptoms presenting themselves. It also involves knowing which data to capture and how to minimize the impact on server performance while still acquiring the necessary information.
Analyzing Extended Events Data
After capturing Extended Events data, it can be analyzed through various means including:
- SSMS Reports: Pre-formatted reports available in SSMS that can provide insights into the data captured by Extended Events.
- Data Export: Exporting the data to an analysis tool such as Excel, Power BI, or other reporting tools for more thorough examination.
- T-SQL Queries: Composing queries against the session data to extract specific information or trends.
In-depth analysis may require correlating data from multiple sources, including Performance Monitor counters, Dynamic Management Views, or other data collected by SQL Server.
Extended Events vs. Profiler and Trace
When SQL Server introduced Extended Events, it also marked a shift away from the older tools of SQL Profiler and Trace. Even though SQL Profiler is still available for use, it is officially deprecated. Extended Events is touted to be a more robust and less resource-intensive choice for modern SQL Server environments.
Comparing the two approaches shows that XEvents offers higher performance, more events, better filtering options, and the capacity to carry out causality tracking for connecting related events. Additionally, Extended Events work across all SQL Server deployments, including on-premises and cloud platforms.
Best Practices for Using Extended Events
Implementing best practices can ensure effective use of Extended Event Sessions within SQL Server. Here are several key points to keep in mind:
- Start with a clear goal for what you need to diagnose or monitor, to avoid collecting unnecessary data.
- Apply precise filters with predicates to minimize performance impact.
- Use appropriate targets that match the diagnostic needs without overwhelming server resources.
- Regularly review and adjust event sessions to ensure they remain relevant and impactful.
- Understand and utilize causality tracking for comprehensive troubleshooting that ties together related events.
- Document sessions and findings for future reference and knowledge sharing within teams.
In conclusion, SQL Server’s Extended Events facilitate a sophisticated and high-performing diagnostic framework that enables deep insights into the operations and performance of a SQL Server instance. When correctly implemented and analyzed, Extended Events can be a game-changer for database administrators and developers, helping effectively identify and resolve issues within their database systems.
