fraction of key-value pairs to keep (between 0 and 1)
output
a "kvConnection" object indicating where the output data should reside (see localDiskConn, hdfsConn). If NULL (default), output will be an in-memory "ddo" object.
overwrite
logical; should existing output location be overwritten? (also can specify overwrite = "backup" to move the existing output to _bak)
control
parameters specifying how the backend should handle things (most-likely parameters to rhwatch in RHIPE) - see rhipeControl and localDiskControl