title: SQL Server 2008 T-SQL select hanging, but not dead locked
body: <p>This is a pretty strange issue so bear with me. I have a stored proc that does some heavy duty processing. When it runs well it usually takes a few minutes depending on server load, but occasionally it appears to get stuck.  </p>
  
  <p>I have looked at the results of <code>sp_who2</code> and what I see is that the process is not blocked, it's still listed as 'RUNNABLE', but the value in disk IO stays the same. Once the process gets in this state it never finishes. If I kill the process and re-execute the stored proc, I usually get the same result.  </p>
  
  <p>Sometimes re-executing the stored proc works, but increasingly I end up having to restart SQL Server. Not ideal...  After restart the stored proc executes as expected. Has anyone even hit a problem like this? Any advice would be greatly appreciated.</p>
  
  <p>Some more context. The stored proc I am executing looks something like this:</p>
  
  <pre><code>delete
  from table1
  
  insert into table1
  select columns
  from 
  (
      select columns
      from giant_table_1 WITH (NOLOCK)
      where condition
      group by columns
  
      UNION
  
      select columns
      from giant_table_2 WITH (NOLOCK)
      where condition
      group by columns
  )
  where condition
  
  more crud on table1
  .
  .
  .
  </code></pre>
  
  <p>If I insert some logging statements into the stored proc I can see that when it hangs it hangs on the insert/select. Wondering if this could be a weird consequence of the NOLOCK statement. We (and by we I mean my boss :)) added the nolock because giant_table_1 and giant_table_2 are constantly being changed. Without the nolock our sproc was getting blocked a lot by other long running processes and vice versa.</p>
  
  <p>Thanks in advance!</p>