Similar to the default trace the system_health session is automatically started up when the instance starts and collects information about what’s going on.

Per BOL you get the following information:

• Errors with a severity of >= 20.
• Memory related errors (Errors 17803, 701, 802, 8645, 8651, 8657 and 8902).
• Non-yielding scheduler problems (Error 17883).
• Deadlocks.
• Sessions that have waited on locks for > 30 seconds.
• Sessions waiting for a long time on preemptive waits (waits on external API calls).
• CLR allocation & virtual allocation failures.
• 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.

Of that the most commonly used (at least in my experience) are the deadlocks and errors, although sessions waiting on locks could be very interesting information too. Note: this isn’t the same data that you see in the default trace.

Ok, so we have the data being collected but where is it being stored? If you look in SSMS you’ll see it has two targets.

And when I scripted mine out I was able to see that the file target is called system_health.xel and a quick directory search (on system_health*.xel) found that it’s not an easy file to locate. Under the Program Files\Microsoft SQL Server\130\Setup Bootstrap\Log\ directory there are date/time directories. Under those are various files including the system_health[big long number].xel

Ok, so now that we know what and where the system_health extended event session is/goes how do we see the data?

Well, I recommend going here. There is a ton of information in there. In general though:

You can open one or more of the files using SSMS:

View target data:

When you view the ring_buffer data it comes out as XML which may or may not be easier to work with depending on your needs.

Watch Live Data

This is going to be new data only, no history.

sys.fn_xe_file_target_read_file

SELECT * FROM sys.fn_xe_file_target_read_file ('system_health*.xel',null,null,null)

Fair warning on this one, again, the event_data is in XML. You have to use XQuery to work with it. The big benefit here is that you can write queries to parse your data and only look at specific things (deadlocks for example).

Filed under: Microsoft SQL Server, SQLServerPedia Syndication, System Functions and Stored Procedures Tagged: default trace, microsoft sql server, system functions