First published on MSDN on Apr 21, 2008
This issue is as old as SQL Server. In fact, it goes back to Sybase days but continues to fool and puzzle administrators.
A session with that status of sleeping / awaiting command is simply a client connection with no active query to the SQL Server. The table below shows the transitions from running to sleeping states for a session.
|
Connect
|
Running
|
|
Connect Completed
|
Sleeping / Awaiting Command
|
|
select @@VERSION
|
Running
|
|
select completed
|
Sleeping / Awaiting Command
|
The question usually arises around a session that is holding locks and its state is sleeping / awaiting command. If the client has an open transaction and the client did not submit a commit or rollback command the state is sleeping / awaiting command. I see this quite often with a procedure that times out.
Create proc myProc
As
Begin tran
Update authors ….
Waitfor delay ’10:00:00’ --- time out will occur here (simulates long workload)
rollback
go
When run from the client with a 30 second query timeout the transaction will remain open because the client indicated it wanted to ‘cancel execution' and do no further processing. To get automatic rollback in this situation transaction abort must be enabled. You now have an open transaction with a SPID sleeping/awaiting command.
The situation can be caused by many other variations but it is always a situation where the SQL Server is waiting for the next command from the client. Outside a physical connection problem these are always application design issues.
Bob Dorr
SQL Server Senior Escalation Engineer
