Problem

After stopping a database backup taking to long to complete (over the network) the associated spid remained in killed/rollback status for several hours.

SPID XX: transaction rollback in progress. Estimated rollback completion: 0%. Estimated time remaining: 0

Solution

As a general rule it is best to not attempt to kill any spid which is performing a database backup.

It seems that, sometimes, operating system level operation initiated from SQL Server can't be rolledback.

After spending quite a few time trying to get rid of the blocked spid the only solution that got me out of this situation was to restart the SQL Server Service.

...

I tried also the solution described in the below posts, but killing the KPID (the id the OS assigns to the thread that is currently bound to the worker executing a task or idling on the spid) didn?t work for me.

Some pro and contra arguments you can find in the below posts (read id carefully before attempting to kill any KPID):

http://sqlserver-qa.net/blogs/perftune/archive/2008/05/06/4120.aspx

http://sqlblog.com/blogs/linchi_shea/archive/2010/02/04/killing-a-sql-server-thread-don-t.aspx