I'm concluding that session 54 is locking resources and preventing updates for the following reasons:

(1) The Command the SPID is referring to is called SELECT INTO, which is the last query I ran against Sandbox and it kept executing without returning results or timing out.

It's the query I cancelled.

(2) Since cancelling it, subsequent queries on that database, which have no reason to run slow eg. ALTER TABLE <tablename> ALTER COLUMN <column name> datetype just took over 3 minutes to complete. .

(3) I'm the only one who touches this db and so I know everything was just fine before the SELECT INTO query.

The SPID is now clocking 140954 CPUTime and 35925 DiskIO, even though I haven't been on the instance for 2 days. No other SPIDs are taking any more than 15 CPU time or 5 DiskIO. Mostly, 0s up and down the sp_who2 columns.

Any reason why I shouldn't be able to kill the SPID regardless of why I think it's the offending one or not? I'm pretty sure it is, but don't know how else to prove it.