title: How to parallel reIndex ElasticSearch
body: <p>I'm trying to reIndex ElasticSearch, I used Scan and Bulk API, but it's very slow, how can I parallel the process to make it faster. 
  My python code as following:</p>
  
  <pre><code>actions=[]
  for hit in helpers.scan(es,scroll='20m',index=INDEX,doc_type=TYPE,params=
       {"size":100}):
      value= hit.get('_source')
      idval = hit.get('_id')
      action = indexAction(INDEX_2,TYPE_2,idval,value)
      actions.append(action)
      count+=1
      if(count%200==0):
          helpers.bulk(es, actions,stats_only=True,params=
          {"consistency":"one","chunk_size":200})
          actions=[]
  </code></pre>
  
  <p>Should I make the scan multiple process or should I make the bulk multiple processes. I've bean wandering how does ElasticSearch-Hadoop to implement this. My index has 10 nodes and 20 shards. </p>