Extended Events in SQL Server

 Extended Events is a lightweight performance monitoring system that enables you to collect data to monitor and troubleshoot problems in SQL Server. It provides a highly scalable and flexible architecture that allows you to define what data to collect, filter the data, and how to store and analyze it.

Key Concepts

• Event: An action or occurrence that you can track. Examples include SQL statements being executed, errors, or waits.
• Session: A collection of events, targets, and other components. You define what events to collect in a session.
• Target: A destination for the event data, such as a file, ring buffer, or event counter.
• Predicate: A filter condition used to limit the data collected by events.
• Action: A task that collects additional data when an event occurs.

Creating and Managing Extended Events Sessions

Creating an Extended Events Session

You can create an Extended Events session using SQL Server Management Studio (SSMS) or T-SQL.

Using SSMS

1. Open SSMS and connect to your SQL Server instance.
2. In Object Explorer, expand the "Management" node, right-click "Extended Events," and select "New Session Wizard."
3. Follow the wizard to create a session by selecting events, targets, and configuring options.

Using T-SQL

Here's an example of creating an Extended Events session using T-SQL:

-- Create a new Extended Events session
CREATE EVENT SESSION [MySession] 
ON SERVER 
ADD EVENT sqlserver.error_reported (
    ACTION (sqlserver.sql_text, sqlserver.database_id)
    WHERE ([severity] >= 16)
),
ADD EVENT sqlserver.sql_statement_completed (
    ACTION (sqlserver.sql_text, sqlserver.database_id)
    WHERE ([duration] > 1000)
)
ADD TARGET package0.ring_buffer
WITH (MAX_MEMORY=4096 KB, EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS, MAX_DISPATCH_LATENCY=30 SECONDS, MAX_EVENT_SIZE=0 KB, MEMORY_PARTITION_MODE=NONE, TRACK_CAUSALITY=OFF, STARTUP_STATE=OFF);
GO

-- Start the session
ALTER EVENT SESSION [MySession] ON SERVER STATE = START;
GO

In this example, the session MySession captures error reports with severity greater than or equal to 16 and SQL statements that took more than 1000 milliseconds to complete. The events are stored in a ring buffer target.

Viewing Extended Events Data

You can view the data collected by an Extended Events session using SSMS or T-SQL.

Using SSMS

1. In Object Explorer, expand the "Extended Events" node, then "Sessions," and find your session.
2. Right-click the session and select "Watch Live Data" to see real-time data.
3. You can also export the data to a file or view historical data by configuring the target.

Using T-SQL

Here's an example of querying the data collected by a session:

-- Query the ring buffer target
SELECT 
    event_data = CONVERT(XML, event_data)
FROM sys.fn_xe_session_targets
    INNER JOIN sys.dm_xe_sessions
        ON sys.fn_xe_session_targets.event_session_address = sys.dm_xe_sessions.address
WHERE sys.dm_xe_sessions.name = 'MySession';

Best Practices for Using Extended Events

1. Filter Data: Use predicates to filter the events and reduce the volume of collected data.
2. Choose Appropriate Targets: Select the right target based on your needs (e.g., ring buffer for in-memory analysis, file target for persistent storage).
3. Monitor Performance: Be mindful of the performance impact. Extended Events are lightweight, but collecting too many events or using extensive actions can affect performance.
4. Automate Sessions: Automate the creation, starting, and stopping of sessions using SQL Agent jobs or scripts to ensure consistent monitoring.
5. Analyze Collected Data: Use tools like SSMS, custom scripts, or third-party tools to analyze the collected data and identify issues or trends.

Extended Events is a powerful tool for SQL Server monitoring and troubleshooting, providing detailed insights into server behavior and performance with minimal overhead.