How to find the deadlock reason in sql server ro14?

Question

Facing a deadlock in SQL server database and can see deadlock entry in SQL logs. How the log entries can be used to find the reason for this deadlock?

Answer 1

Deadlock information is captured by the system_health Extended Events trace by default. No need to turn on additional trace flags.

Information from the xml_deadlock event can be viewed from SSMS Object Explorer (Management-->Extended Events-->Sessions--system_health) or with T-SQL. Below is an example query to get the deadlock xml from the file target. You can also save the deadlock xml to a file with an xdl extension and open the file in SSMS for a graphical view of the deadlock.

--get xml_deadlock_report from system_health session file target
WITH
      --get full path to current system_health trace file
      CurrentSystemHealthTraceFile AS (
        SELECT CAST(target_data AS xml).value('(/EventFileTarget/File/@name)[1]', 'varchar(255)') AS FileName
        FROM sys.dm_xe_session_targets
        WHERE
            target_name = 'event_file'
            AND CAST(target_data AS xml).value('(/EventFileTarget/File/@name)[1]', 'varchar(255)') LIKE '%\system[_]health%'
    )
      --get trace folder name and add base name of system_health trace file with wildcard
    , BaseSystemHealthFileName AS (
        SELECT 
            REVERSE(SUBSTRING(REVERSE(FileName), CHARINDEX(N'\', REVERSE(FileName)), 255)) + N'system_health*.xel' AS FileNamePattern
        FROM CurrentSystemHealthTraceFile
        )
      --get xml_deadlock_report events from all system_health trace files
    , DeadLockReports AS (
        SELECT CAST(event_data AS xml) AS event_data
        FROM BaseSystemHealthFileName
        CROSS APPLY sys.fn_xe_file_target_read_file ( FileNamePattern, NULL, NULL, NULL) AS xed
        WHERE xed.object_name like 'xml_deadlock_report'
    )
--display 10 most recent deadlocks
SELECT TOP 10
      DATEADD(hour, DATEDIFF(hour, SYSUTCDATETIME(), SYSDATETIME()), event_data.value('(/event/@timestamp)[1]', 'datetime2')) AS LocalTime
    , event_data AS DeadlockReport
FROM DeadLockReports
ORDER BY LocalTime ASC;

Answer 2

This code will display the error log which contains the query that creates the deadlock. IF OBJECT_ID('tempdb.dbo.ErrorLog') IS Not Null BEGIN DROP TABLE tempdb.dbo.ErrorLog END

 CREATE TABLE tempdb.dbo.ErrorLog 
 (Id int IDENTITY (1, 1) NOT NULL, 
  logdate DATETIME, procInfo VARCHAR(10), 
  ERRORLOG VARCHAR(MAX))

  -- insert the actual data from the Error log into our newly created table.

 INSERT INTO tempdb.dbo.ErrorLog
 EXEC master.dbo.sp_readerrorlog


declare @sql nvarchar(max)
set @sql='select logdate, procInfo, ERRORLOG from tempdb.dbo.ErrorLog 
where Id >= (select top 1 id  from tempdb.dbo.ErrorLog WHERE ERRORLOG Like 
''%deadlock-list%'' order by id desc)'
select @SQL

Answer 3

Deadlock information can be captured in the SQL Server Error Log or by using Profiler / Server Side Trace.

• 1204 - this provides information about the nodes involved in the deadlock
• 1222 - returns deadlock information in an XML format

You can turn on each of these separately or turn them on together.

To turn these on you can issue the following commands in a query window or you can add these as startup parameters. If these are turned on from a query window, the next time SQL Server starts these trace flags will not be active, so if you always want to capture this data the startup parameters is the best option.

DBCC TRACEON (1204, -1)
DBCC TRACEON (1222, -1)

Please refer to the following Links for more details

• Redgate
• MS SQL Tips