title: When do I need to use sfExport (R Snowfall package)
body: <p>I am using snowfall for parallel computing. I am always on only one machine with multiple CPUs (>20 cores). I am processing a large amount of data (>20gb). sfExport() takes very long.</p>
  
  <p>When I run my test codes on my laptop and check the CPU usage, it sometimes also works without sfExport(). </p>
  
  <p>Some parts of my codes are nested sfLapply() functions. Like:</p>
  
  <pre><code>func2 &lt;- function(c,d, ...) {      
  
    result &lt;- 
      list(x = c+d,
           y = ..,
           ...
           )
  
    return(result)
  
  }
  
  func1 &lt;- function(x, a, b, c, ...) {
  
    library(snowfall)
    d &lt;- a+b
  
    result &lt;- sfLapply(as.list(b$row), func2, c, d, ...)
  
    return(result)
  }
  
  result &lt;- sfLapply(as.list(data.table$row), func1, a, b, c, ..)
  </code></pre>
  
  <p>When do I really need to export the data to all CPUs?</p>
  
  <p>thanks and best regards
  Nico</p>