title: SQL: NOLOCK causes query slow down
body: <p>Is there any reason why adding a nolock to a query would cause it to increase execution time?</p>
  
  <pre><code>UPDATE TargetTable
        SET col1 = c1.RowCnt,
        col2 = c2.RowCnt
      from TargetTable tt
      join 
      (
        select col3, RowCnt = NULLIF(COUNT(*),0) from Table2 (nolock)
        group by col3
      ) c1 on c1.col3 = tt.ID 
      join
      (
        select col4, RowCnt = NULLIF(COUNT(*),0) from Table2 (nolock) 
        group by col4
      ) c2 on c2.col4 = tt.ID 
  
        WHERE timestamp BETWEEN @FromDate AND @ToDate
        AND (tt.Client_ID = @Client_ID)
  </code></pre>