The system_health session is an Extended Events session that is included by default with SQL Server. This session starts automatically when the SQL Server Database Engine starts, and runs without any noticeable performance effects. The session collects system data that you can use to help troubleshoot performance issues in the Database Engine. Therefore, we recommend that you do not stop or delete the session.
The session collects information that includes the following:
The sql_text and session_id for any sessions that encounter an error that has a severity >=20.
The sql_text and session_id for any sessions that encounter a memory-related error. The errors include 17803, 701, 802, 8645, 8651, 8657 and 8902.
A record of any non-yielding scheduler problems. (These appear in the SQL Server error log as error 17883.)
Any deadlocks that are detected.
The callstack, sql_text, and session_id for any sessions that have waited on latches (or other interesting resources) for > 15 seconds.
The callstack, sql_text, and session_id for any sessions that have waited on locks for > 30 seconds.
The callstack, sql_text, and session_id for any sessions that have waited for a long time for preemptive waits. The duration varies by wait type. A preemptive wait is where SQL Server is waiting for external API calls.
The callstack and session_id for CLR allocation and virtual allocation failures.
The ring_buffer events for the memory broker, scheduler monitor, memory node OOM, security, and connectivity.
System component results from sp_server_diagnostics.
Instance health collected by scheduler_monitor_system_health_ring_buffer_recorded.
CLR Allocation failures.
Connectivity errors using connectivity_ring_buffer_recorded.
Security errors using security_error_ring_buffer_recorded.
Viewing the Session Data
The session uses the ring buffer target to store the data. To view the session data, use the following query:
SELECT CAST(xet.target_data as xml) FROM sys.dm_xe_session_targets xet JOIN sys.dm_xe_sessions xe ON (xe.address = xet.event_session_address) WHERE xe.name = 'system_health'
To view the session data from the event file, use the Extended Events user interface available in Management Studio. For more information, see Advanced Viewing of Target Data from Extended Events in SQL Server.
Restoring the system_health Session
If you delete the system_health session, you can restore it by executing the u_tables.sql file in Query Editor. This file is located in the following folder, where C: represents the drive where you installed the SQL Server program files:
C:\Program Files\Microsoft SQL Server\MSSQL13.<instanceid>\MSSQL\Install
Be aware that after you restore the session, you must start the session by using the ALTER EVENT SESSION statement or by using the Extended Events node in Object Explorer. Otherwise, the session starts automatically the next time that you restart the SQL Server service.