title: SOLR - delete documents depending on index size
body: <p>I want to purge SOLR index whenever the index occupies more than 10% of the total disk space. The purge should result in deletion of the oldest documents that will bring the index space to less than 10% of the total space. How can I go about finding these oldest documents? </p>
  
  <p>I thought of finding the size of a single document and using that as the base to determine how many docs to delete(sort by date asc and rows = N). Is there an other way to go about it? Thanks.</p>