SQL SERVER – Identifying Blocking Chain Using SQL Scripts

Here is a script that shows the full blocking chain. There are a number of blog posts that have been written on this very topic. This can be from basics to almost advanced in many ways. I am outlining some of them here below:

• SQL SERVER – Quickest Way to Identify Blocking Query and Resolution – Dirty Solution
• SQL SERVER – SSMS: Activity – All Blocking Transactions
• SQL SERVER – Find Blocking Using Blocked Process Threshold
• SQL SERVER – Activity Monitor to Identify Blocking – Find Expensive Queries

If these were not enough, I wanted to play around with some SQL Scripts for this basic deadlock behavior. The most basic script I have been using and used by many DBA will include Activity Monitor, sp_who2, sysprocesses etc.

Recently I saw a script written by a DBA friend:

SELECT * FROM sys.dm_os_waiting_tasks
WHERE blocking_session_id IS NOT NULL
GO

This shows the rows like:

This is so cool because I know who is waiting for whom. In the above image 53 is waiting for 68. While 79 is waiting for 53. This was a cool way to look at things.

I wanted to show the same data in slightly different way using T-SQL. So I wrote a Blocking Tree TSQL script.

SET NOCOUNT ON
GO
SELECT SPID, BLOCKED, REPLACE (REPLACE (T.TEXT, CHAR(10), ' '), CHAR (13), ' ' ) AS BATCH
INTO #T
FROM sys.sysprocesses R CROSS APPLY sys.dm_exec_sql_text(R.SQL_HANDLE) T
GO
WITH BLOCKERS (SPID, BLOCKED, LEVEL, BATCH)
AS
(
SELECT SPID,
BLOCKED,
CAST (REPLICATE ('0', 4-LEN (CAST (SPID AS VARCHAR))) + CAST (SPID AS VARCHAR) AS VARCHAR (1000)) AS LEVEL,
BATCH FROM #T R
WHERE (BLOCKED = 0 OR BLOCKED = SPID)
AND EXISTS (SELECT * FROM #T R2 WHERE R2.BLOCKED = R.SPID AND R2.BLOCKED <> R2.SPID)
UNION ALL
SELECT R.SPID,
R.BLOCKED,
CAST (BLOCKERS.LEVEL + RIGHT (CAST ((1000 + R.SPID) AS VARCHAR (100)), 4) AS VARCHAR (1000)) AS LEVEL,
R.BATCH FROM #T AS R
INNER JOIN BLOCKERS ON R.BLOCKED = BLOCKERS.SPID WHERE R.BLOCKED > 0 AND R.BLOCKED <> R.SPID
)
SELECT N'    ' + REPLICATE (N'|         ', LEN (LEVEL)/4 - 1) +
CASE WHEN (LEN(LEVEL)/4 - 1) = 0
THEN 'HEAD -  '
ELSE '|------  ' END
+ CAST (SPID AS NVARCHAR (10)) + N' ' + BATCH AS BLOCKING_TREE
FROM BLOCKERS ORDER BY LEVEL ASC
GO
DROP TABLE #T
GO

The output would look like:

This is a cool way to look at the same Blocking data inside SSMS. I have taken a simple way to show this script. I am sure this can be beautified more with your help. So if you use this and modify the same. Do post them over comments too. That is a great way to enhance the Blocking Tree Script.

Published by Pinal Dave on SQLAuthority. More of my work at pinaldave.com.