This blog has moved, permanently, to

Tuesday, July 21, 2009

SQL Server Locking, Blocking and Waiting

Being able to see what is blocking or waiting on a SQL Server machine is essential for most developers these days. I find myself using the following queries almost daily at the moment, so I thought I'd post them here:

    tx.[text] as ExecutingSQL, 
from sys.dm_os_waiting_tasks wt
inner join sys.dm_exec_connections ec on wt.session_id = ec.session_id
cross apply 
    select * from sys.dm_exec_sql_text(ec.most_recent_sql_handle)
) as tx
where wt.session_id > 50 and wt.wait_duration_ms > 0

    Blocked.session_id as Blocked_Session_ID
    ,Blocked_SQL.text as Blocked_SQL
    ,waits.wait_type as Blocked_Resource
    ,Blocking.session_id as Blocking_Session_ID
    ,Blocking_SQL.text as Blocking_SQL
from sys.dm_exec_connections as Blocking
inner join sys.dm_exec_requests as Blocked on Blocked.blocking_session_id = Blocking.session_id
cross apply
    select * from sys.dm_exec_sql_text(Blocking.most_recent_sql_handle)
) AS Blocking_SQL
cross apply
    select * from sys.dm_exec_sql_text(Blocked.sql_handle)
) as Blocked_SQL
inner join sys.dm_os_waiting_tasks as waits on waits.session_id = Blocked.session_id

Wednesday, July 1, 2009

SQL Server IDENTITY Columns

IDENTITY columns can be a real pain in the ass when data gets out of sync. GUIDs are generally a much better option when it comes to replication, but you aren't always in control of data structures and sometimes you inherit old systems that weren't designed to be replicated.

That being said, here are some tips on how to get around problems with IDENTITY columns and getting data in sync:


You can temporarily turn identity insertion off with the following statement:
SET IDENTITY_insert <table> ON
You can now insert the identity values into your table. Don't forget to run the same statement on the table, substituting ON for OFF!

Reseeding the IDENTITY value

For example, if you want to reset the current identity value on a table to 100, you can use the following statement:
 'schema.table', RESEED, 100