title: SQLAlchemy `.fetchmany()` vs `.limit()`
body: <p>Assuming <code>query</code> is some already defined query. As far as I can tell, <code>connection.execute(query).fetchmany(n)</code> and <code>connection.execute(query).limit(n).fetchall()</code> apparently return the same result set. I'm wondering if one of them is more idiomatic or — more importantly — more performant?</p>
  
  <p>Example usage would be:  </p>
  
  <pre class="lang-py prettyprint-override"><code>query = select([census.columns.state, (census.columns.pop2008 - census.columns.pop2000).label("pop_change")]).group_by(census.columns.state).order_by(desc("pop_change"))
  results_1 = query.limit(5).fetchall()
  results_2 = connection.execute(query).fetchmany(n)    #`results_2` = `results_1`
  </code></pre>