At my current consulting contract, we were running into a lot of deadlocks. It's been a long time since I analyzed deadlocks. And the system I'm working on had
a lot of them, right after we had a very sudden and extreme increase in usage.
There were so many deadlocks that we needed to be efficient in deciding which ones to fix first. So I researched. I hit a lot of dead ends, and ran into a lot of advertising for specific database monitoring tools. But it turns out that there's some very good deadlock reporting, built right into SQL Server, out of the box.
Basically, SQL Server Extended events can be queried for deadlock occurrences. You have to use XML querying, with nodes, but there's plenty of examples online. The script I started out with is the one here:
Querying Deadlocks From System_Health XEvent. I made some modifications to be able to do more analysis without constantly rerunning the base query, which takes a while.
So,
Step 1 is to run the below, which creates a global temp table called ##DeadlockReporting, which can be queried later.
if object_id('tempdb..##DeadlockReporting') is not null drop table tempdb..##DeadlockReporting
DECLARE @SessionName SysName
SELECT @SessionName = 'system_health'
/*
SELECT Session_Name = s.name, s.blocked_event_fire_time, s.dropped_buffer_count, s.dropped_event_count, s.pending_buffers
FROM sys.dm_xe_session_targets t
INNER JOIN sys.dm_xe_sessions s ON s.address = t.event_session_address
WHERE target_name = 'event_file'
--*/
IF OBJECT_ID('tempdb..#Events') IS NOT NULL BEGIN
DROP TABLE #Events
END
DECLARE @Target_File NVarChar(1000)
, @Target_Dir NVarChar(1000)
, @Target_File_WildCard NVarChar(1000)
SELECT @Target_File = CAST(t.target_data as XML).value('EventFileTarget[1]/File[1]/@name', 'NVARCHAR(256)')
FROM sys.dm_xe_session_targets t
INNER JOIN sys.dm_xe_sessions s ON s.address = t.event_session_address
WHERE s.name = @SessionName
AND t.target_name = 'event_file'
SELECT @Target_Dir = LEFT(@Target_File, Len(@Target_File) - CHARINDEX('\', REVERSE(@Target_File)))
SELECT @Target_File_WildCard = @Target_Dir + '\' + @SessionName + '_*.xel'
--Keep this as a separate table because it's called twice in the next query. You don't want this running twice.
SELECT DeadlockGraph = CAST(event_data AS XML)
, DeadlockID = Row_Number() OVER(ORDER BY file_name, file_offset)
INTO #Events
FROM sys.fn_xe_file_target_read_file(@Target_File_WildCard, null, null, null) AS F
WHERE event_data like '<event name="xml_deadlock_report%'
;WITH Victims AS
(
SELECT VictimID = Deadlock.Victims.value('@id', 'varchar(50)')
, e.DeadlockID
FROM #Events e
CROSS APPLY e.DeadlockGraph.nodes('/event/data/value/deadlock/victim-list/victimProcess') as Deadlock(Victims)
)
, DeadlockObjects AS
(
SELECT DISTINCT e.DeadlockID
, ObjectName = Deadlock.Resources.value('@objectname', 'nvarchar(256)')
FROM #Events e
CROSS APPLY e.DeadlockGraph.nodes('/event/data/value/deadlock/resource-list/*') as Deadlock(Resources)
)
SELECT *
Into ##DeadlockReporting
FROM
(
SELECT
e.DeadlockID
,TransactionTime = Deadlock.Process.value('@lasttranstarted', 'datetime')
, DeadlockGraph
, DeadlockObjects = substring((SELECT (', ' + o.ObjectName)
FROM DeadlockObjects o
WHERE o.DeadlockID = e.DeadlockID
ORDER BY o.ObjectName
FOR XML PATH ('')
), 3, 4000)
, Victim = CASE WHEN v.VictimID IS NOT NULL
THEN 1
ELSE 0
END
, SPID = Deadlock.Process.value('@spid', 'int')
, ProcedureName = Deadlock.Process.value('executionStack[1]/frame[1]/@procname[1]', 'varchar(200)')
, LockMode = Deadlock.Process.value('@lockMode', 'char(1)')
, Code = Deadlock.Process.value('executionStack[1]/frame[1]', 'varchar(1000)')
, ClientApp = CASE LEFT(Deadlock.Process.value('@clientapp', 'varchar(100)'), 29)
WHEN 'SQLAgent - TSQL JobStep (Job '
THEN 'SQLAgent Job: ' + (SELECT name FROM msdb..sysjobs sj WHERE substring(Deadlock.Process.value('@clientapp', 'varchar(100)'),32,32)=(substring(sys.fn_varbintohexstr(sj.job_id),3,100))) + ' - ' + SUBSTRING(Deadlock.Process.value('@clientapp', 'varchar(100)'), 67, len(Deadlock.Process.value('@clientapp', 'varchar(100)'))-67)
ELSE Deadlock.Process.value('@clientapp', 'varchar(100)')
END
, HostName = Deadlock.Process.value('@hostname', 'varchar(20)')
, LoginName = Deadlock.Process.value('@loginname', 'varchar(20)')
, InputBuffer = Deadlock.Process.value('inputbuf[1]', 'varchar(1000)')
FROM #Events e
CROSS APPLY e.DeadlockGraph.nodes('/event/data/value/deadlock/process-list/process') as Deadlock(Process)
LEFT JOIN Victims v ON v.DeadlockID = e.DeadlockID AND v.VictimID = Deadlock.Process.value('@id', 'varchar(50)')
) X --In a subquery to make filtering easier (use column names, not XML parsing), no other reason
ORDER BY TransactionTime DESC
Now I have a global temp table called ##DeadlockReporting.
Step 2 is to run queries against it. Here's some that I wrote up. The most useful is the one with the header "Get the worst offenders in past 24 hours". This will give you a good picture of the deadlock—the affected tables, the stored procedures that are being called, the specific problem code. Then, click on the DeadlockXML in order to see the full details of the deadlock.
You may find some really obvious targets for fixes that need to be made. I found some update statements that contained subqueries in the Set clause that needed to be fixed.
Select top 100 * From ##DeadlockReporting order by TransactionTime desc
-- Get the worst offenders in past 24 hours
-- Click on the DeadlockXML to show details
Select
DeadlockObjects
,ProcedureName
,Code = min(Code)
,DeadlockXML = convert(xml, min(convert(varchar(max), DeadlockGraph) ))
,FirstDeadlock = Min(TransactionTime)
,LastDeadlock = Max(TransactionTime)
,PresumedTotalDeadlocks = Count(*)
from ##DeadlockReporting
Where TransactionTime >= dateadd (hh, -24, getdate() )
Group by
DeadlockObjects
,ProcedureName
Order by Count(*) desc
-- Get summary past 24 hours, by hour
;with DeadlockReportingFormatted as (
Select
TransactionHour_UTC = convert(varchar(13), TransactionTime, 120) + ':00'
,TransactionHour_PST =
convert(varchar(13), TransactionTime AT TIME ZONE 'UTC' AT TIME ZONE 'Pacific Standard Time', 120)
+ ':00'
,*
from ##DeadlockReporting
)
Select
TransactionHour_UTC
,TransactionHour_PST
,DeadlockObjects
,ProcedureName
,PresumedTotalDeadlocks = Count(*)
From DeadlockReportingFormatted
Where TransactionTime >= dateadd(hh, -24, getdate())
Group by
TransactionHour_UTC
,TransactionHour_PST
,DeadlockObjects
,ProcedureName
Order by
TransactionHour_UTC desc
,PresumedTotalDeadlocks desc
