pointers, solutions and scripts for the SQL DBA
not intended to replace msdn, common sense or oxford commas

4/19/2012

Using sys.dm_exec_requests to find a blocking chain and much more

As with every good DBA's toolbox, my blocking list query using sys.dm_exec_requests is evolving.

I've added the following features:
  • The query execution plan of the active request in the QueryPlan column to the right.
  • Variable at the top which changes the relationship of the join between sys.dm_exec_sessions and  sys.dm_exec_requests. 
    • When set to 0, this query now displays all sessions, even those without active requests.  I recently found this helpful when researching sleeping sessions that were blocking active sessions.
    • When set to 1, this query displays as it used to - only session and active request data.  
  • Percent_Complete column - great for finding the progress of backup and restores 
  • A few other minor helpful columns
Update March 4, 2014:
  • Added Transaction Isolation Level for Session and Request
  • Added Status for Session and Request
  • Added Login_name, Client_Interface_name
Update June 24, 2016:
  • Added resource governor group and pool identifiers
  • Bugfix for sometimes when the offset text wouldn't display anything
 declare @showallspids bit 
 select @showallspids =1

 create table #ExecRequests  (
  id int IDENTITY(1,1) PRIMARY KEY
 , session_id smallint not null 
 , request_id int null
 , request_start_time datetime null
 , login_time datetime not null
 , login_name nvarchar(256) null
 , client_interface_name nvarchar(64)
 , session_status nvarchar(60) null
 , request_status nvarchar(60) null
 , command nvarchar(32) null
 , sql_handle varbinary(64) null
 , statement_start_offset int null
 , statement_end_offset int null
 , plan_handle varbinary (64) null
 , database_id smallint null
 , user_id int null
 , blocking_session_id smallint null
 , wait_type nvarchar (120) null
 , wait_time_s int null
 , wait_resource nvarchar(120) null
 , last_wait_type nvarchar(120) null
 , cpu_time_s int null
 , tot_time_s int null
 , reads bigint null
 , writes bigint null
 , logical_reads bigint null
 , [host_name] nvarchar(256) null
 , [program_name] nvarchar(256) null
 , Governor_Group_Id int null
 , blocking_these varchar(1000) NULL
 , percent_complete int null
 , session_transaction_isolation_level varchar(20) null
 , request_transaction_isolation_level varchar(20) null
 )


 insert into #ExecRequests (session_id,request_id, request_start_time, login_time, login_name, client_interface_name, session_status, request_status, command,sql_handle,statement_start_offset,statement_end_offset,plan_handle,database_id,user_id,blocking_session_id,wait_type,last_wait_type,wait_time_s,wait_resource,cpu_time_s,tot_time_s,reads,writes,logical_reads,[host_name], [program_name] , session_transaction_isolation_level , request_transaction_isolation_level , Governor_Group_Id)
 select s.session_id,request_id, r.start_time, s.login_time, s.login_name, s.client_interface_name, s.status, r.status,command,sql_handle,statement_start_offset,statement_end_offset,plan_handle,r.database_id,user_id,blocking_session_id,wait_type,r.last_wait_type, r.wait_time/1000.,r.wait_resource ,r.cpu_time/1000.,r.total_elapsed_time/1000.,r.reads,r.writes,r.logical_reads,s.[host_name], s.[program_name], s.transaction_isolation_level, r.transaction_isolation_level, s.group_id 
 from sys.dm_exec_sessions s 
 left outer join sys.dm_exec_requests r on r.session_id = s.session_id
 where 1=1
 and s.session_id >= 50 --retrieve only user spids
 and s.session_id <> @@SPID --ignore myself
 and  (@showallspids = 1 or r.session_id is not null) 

 print 'insert done'

 update #ExecRequests 
 set blocking_these = LEFT((select isnull(convert(varchar(5), er.session_id),'') + ', ' 
       from #ExecRequests er
       where er.blocking_session_id = isnull(#ExecRequests.session_id ,0)
       and er.blocking_session_id <> 0
       FOR XML PATH('') 
       ),1000)
 
 print 'update done'

 select * from 
 (
  select  
   timestamp = getdate()
  , r.session_id , r.host_name , r.program_name
  , r.session_status
  , r.request_status
  , r.blocking_these
  , blocked_by =  r.blocking_session_id
  , r.wait_type 
  , r.wait_resource
  , r.last_wait_type
  , DBName = db_name(r.database_id)
  , est.objectid
  , r.command
  , login_time
  , login_name
  , client_interface_name
  , request_start_time
  , r.tot_time_s, r.wait_time_s
  , r.cpu_time_s --cpu_time is not accurate prior to SQL Server 2012 SP2.  http://blogs.msdn.com/b/psssql/archive/2014/11/11/how-come-sys-dm-exec-requests-cpu-time-never-moves.aspx
  , r.reads, r.writes, r.logical_reads
  --, [fulltext] = est.[text]
  , offsettext = CASE WHEN r.statement_start_offset = 0 and r.statement_end_offset= 0 THEN left(est.text, 4000)
         ELSE SUBSTRING (  est.[text]
             , r.statement_start_offset/2 + 1, 
              CASE WHEN r.statement_end_offset = -1 THEN LEN (CONVERT(nvarchar(max), est.[text])) 
               ELSE r.statement_end_offset/2 - r.statement_start_offset/2 + 1
              END )
       END
  , r.statement_start_offset, r.statement_end_offset
  , cacheobjtype = LEFT (p.cacheobjtype + ' (' + p.objtype + ')', 35)
  , QueryPlan  = qp.query_plan 
  , request_transaction_isolation_level = case request_transaction_isolation_level 
    when 0 then 'Unspecified'
    when 1 then 'ReadUncommitted'
    when 2 then 'ReadCommitted'
    when 3 then 'Repeatable'
    when 4 then 'Serializable'
    when 5 then 'Snapshot' end 
  , session_transaction_isolation_level = case session_transaction_isolation_level 
    when 0 then 'Unspecified'
    when 1 then 'ReadUncommitted'
    when 2 then 'ReadCommitted'
    when 3 then 'Repeatable'
    when 4 then 'Serializable'
    when 5 then 'Snapshot' end 
  , p.plan_handle
  , stat.execution_count, total_worker_time_s = stat.total_worker_time/1000./1000., last_worker_time_s = stat.last_worker_time/1000./1000., total_elapsed_time_s = stat.total_elapsed_time/1000./1000., last_elapsed_time_s = stat.last_elapsed_time/1000./1000., stat.total_physical_reads, stat.total_logical_writes, stat.total_logical_reads
  , Governor_Group_Name = wg.name
  , Governor_Group_ID  = r.Governor_Group_Id
  , Governor_Pool_Name = wp.name 
  , Governor_Pool_ID  = wg.Pool_id
  --next two lines are SQL 2012 only!
  --, stat.total_rows, stat.last_rows
  from #ExecRequests r
  LEFT OUTER JOIN sys.dm_exec_cached_plans p ON p.plan_handle = r.plan_handle 
  OUTER APPLY sys.dm_exec_query_plan (r.plan_handle) qp
  OUTER APPLY sys.dm_exec_sql_text (r.sql_handle) est
  LEFT OUTER JOIN sys.dm_exec_query_stats stat on stat.plan_handle = r.plan_handle
  and r.statement_start_offset = stat.statement_start_offset  
  and r.statement_end_offset = stat.statement_end_offset
  LEFT OUTER JOIN sys.resource_governor_workload_groups  wg
  on wg.group_id = r.Governor_Group_Id
  LEFT OUTER JOIN sys.resource_governor_resource_pools wp
  on wp.pool_id = wg.Pool_id
  
 
 ) a
 order by LEN(blocking_these) desc, blocking_these desc, blocked_by desc, session_id asc
 
 print 'done'
 go
 drop table #ExecRequests  
 


3 comments:

  1. Msg 102, Level 15, State 1, Line 101
    Incorrect syntax near '.'.

    ReplyDelete
  2. Anonymous-
    Look out for SQL 2000 compatibility databases or SQL 2000 instances. I can reproduce your error only by running the script in the context of a database in SQL database in Compatibility Level 80.
    This script, like any script that uses a DMV, won't work for SQL 2000.

    ReplyDelete
  3. Thanks for the post - very helpful!

    ReplyDelete

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