title: Dask Dataframe: Get row count?
body: <p>Simple question: I have a dataframe in dask containing about 300 mln records. I need to know the exact number of rows that the dataframe contains. Is there an easy way to do this?</p>
  
  <p>When I try to run <code>dataframe.x.count().compute()</code> it looks like it tries to load the entire data into RAM, for which there is no space and it crashes.</p>