CSS SQL Server Engineers

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How It Works: What is a Sleeping / Awaiting Command Session

How It Works: What is a Sleeping / Awaiting Command Session

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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

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