Deadlock troubleshooting in Sql Server 2008

Question

My website doesn\'t seem to handle a high number of visitors, I believe it\'s because the server is too simple.

2 hours ago my website was getting a lot of hits and

Answer 1

SQL Server 2008 has multiple ways to identify processes and queries involved in deadlock.

1. If deadlocks are easy to reproduce,frequency is higher and you can profile SQL server (you have the access and performance cost on server when profiler is enabled) using SQL Profiler will give you nice graphical view of deadlock. This page has all the information you need to use deadlock graphs http://sqlmag.com/database-performance-tuning/gathering-deadlock-information-deadlock-graph

2. Most of the times reproducing deadlocks is hard, or they happen in production environment where we dont want to attach Profiler to it and affect performance.

I would use this query to get deadlocks happened:

SELECT
  xed.value('@timestamp', 'datetime') as Creation_Date,
  xed.query('.') AS Extend_Event
FROM
(
  SELECT CAST([target_data] AS XML) AS Target_Data
  FROM sys.dm_xe_session_targets AS xt
  INNER JOIN sys.dm_xe_sessions AS xs
  ON xs.address = xt.event_session_address
  WHERE xs.name = N'system_health'
  AND xt.target_name = N'ring_buffer'
) AS XML_Data
CROSS APPLY Target_Data.nodes('RingBufferTarget/event[@name="xml_deadlock_report"]') AS XEventData(xed)
ORDER BY Creation_Date DESC

I would NOT go in the direction of using (NOLOCK) to fix deadlocks. That is slippery slope and hiding the original problem.

Answer 2

If you don't mind dirty reads you can try putting (NOLOCK) after your table names in your SELECT queries. The trade off here is that you are not guaranteed the most up to date data as UPDATE and INSERT statements currently executing are ignored.

Usually this is not to much of a train-smash as most systems read far more than they update/insert, but obviously it depends on the nature of your application.

Alternatively have a look at http://www.sql-server-performance.com/tips/deadlocks_p1.aspx

Answer 3

Writes will block reads on SQL Server, unless you have row versioning enabled. You should use the sp_who2 stored procedure and a SQL Profiler trace. sp_who2 will tell you which processes are blocking which, and the profiler will tell you what the last statement was for the blocking process.