title: How to reindex ElasticSearch quickly?
body: <p>I have an ElasticSearch index with around 200M documents, total index size of 90Gb.</p>
  
  <p>I changed mapping, so I would like ElasticSearch to re-index all the documents.</p>
  
  <p>I wrote a script that creates a new index (with the new mapping), then goes over all the documents in the old index and puts then into the new one.</p>
  
  <p>It seems to work, but the problem is that it works extremely slowly.
  It started with 300 documents / minute two days ago, and now the speed is 150 documents/minute.</p>
  
  <p>The script runs on a machine within the same network the elastic search machines in.</p>
  
  <p>With such speed it will require a month for the re-index to finish.</p>
  
  <p>Does anybody know about some faster technique to re-index an elastic search index?</p>