title: Optimal chunksize parameter in pandas.DataFrame.to_sql
body: <p>Working with a large pandas DataFrame that needs to be dumped into a PostgreSQL table.  From what I've read it's not a good idea to dump all at once, (and I was locking up the db) rather use the <a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_sql.html" rel="noreferrer"><code>chunksize</code></a> parameter.  The answers <a href="https://stackoverflow.com/questions/11622652/large-persistent-dataframe-in-pandas">here</a> are helpful for workflow, but I'm just asking about the value of chunksize affecting performance.</p>
  
  <pre><code>In [5]: df.shape
  Out[5]: (24594591, 4)
  
  In [6]: df.to_sql('existing_table',
                    con=engine, 
                    index=False, 
                    if_exists='append', 
                    chunksize=10000)
  </code></pre>
  
  <p>Is there a recommended default and is there a difference in performance when setting the parameter higher or lower?  Assuming I have the memory to support a larger chunksize, will it execute faster?</p>