Deadlock graph from Extended Events not showing

Question

I have this query which is from "Sql Server 2017 Query Performance Tuning"(a book). Code for the book can be found here: https://github.com/Apress/sql-server-2017-query-perf-tuning

DECLARE @path NVARCHAR(260)
--to retrieve the local path of system_health files 
SELECT @path = dosdlc.path
FROM sys.dm_os_server_diagnostics_log_configurations AS dosdlc;

SELECT @path = @path + N'system_health_*';

WITH fxd
AS (SELECT CAST(fx.event_data AS XML) AS Event_Data
    FROM sys.fn_xe_file_target_read_file(@path,
                                         NULL,
                                         NULL,
                                         NULL) AS fx )
SELECT dl.deadlockgraph
FROM
(   SELECT dl.query('.') AS deadlockgraph
    FROM fxd
        CROSS APPLY event_data.nodes('(/event/data/value/deadlock)') AS d(dl) ) AS dl;

It is supposed to capture the deadlock graph from Extended Events. I just generated a deadlock following this example (How to simulate DEADLOCK on SQL Server?).

But when I run the query I get an empty result set.

Answer 1

It looks like your XML path specification is for a XE ring buffer target instead of file target. Try the query below.

--Get xml_deadlock_report events from system_health session file target
WITH
      --get trace folder path and append session name with wildcard (assumes base file name is same as session name)
      all_trace_files AS (
        SELECT path + '\system_health*.xel' AS FileNamePattern
        FROM sys.dm_os_server_diagnostics_log_configurations
        )
      --get xml_deadlock_report events from all system_health trace files
    , deadlock_reports AS (
        SELECT CAST(event_data AS xml) AS deadlock_report_xml
        FROM all_trace_files
        CROSS APPLY sys.fn_xe_file_target_read_file ( FileNamePattern, NULL, NULL, NULL) AS trace_records
        WHERE trace_records.object_name like 'xml_deadlock_report'
    )
SELECT
      deadlock_report_xml.value('(/event/@timestamp)[1]', 'datetime2') AS UtcTimestamp
    , deadlock_report_xml AS DeadlockReportXml
FROM deadlock_reports;

To see the graphical deadlock report in SSMS, remove the opening/closing event/data/value tags from the start/end of the XML document and save as a file with extension ".xdl". Then open the file in SSMS to see the deadlock graph.