title: Elasticsearch rolling upgrade - do deleted documents get removed?
body: <p>I'm going to upgrade Elasticsearch from 5.6 to 6.8 following the <a href="https://www.elastic.co/guide/en/elasticsearch/reference/6.8/rolling-upgrades.html" rel="nofollow noreferrer">rolling upgrade procedure</a>.</p>
  <p>I have an index which is 54,172,622 documents across 5 primary shards, with 1 replica of each. There are 21,696,332 deleted documents in the index.</p>
  <p>When I follow the rolling upgrade procedure, will the procedure automatically purge the deleted documents, or is it better to reindex to a new index before upgrading? I assume the upgrade is slower if the deleted documents are included.</p>