Formula for open file descriptors

[Lance Norskog]

Hi-
 
In early June Mike Klass posted a formula for the number of file descriptors
needed by Solr:
 
        For each segment, 7 + num indexed fields per segment.  
        There should be log_{base mergefactor}(numDocs) * mergeFactor
segments, approximately. 

Is this still true?

Thanks,

Lance Norskog