title: What is the use case for index closing in ElasticSearch?
body: <p>I have found out that ES index could be closed.
  <a href="https://www.elastic.co/guide/en/elasticsearch/reference/6.3/indices-open-close.html" rel="noreferrer">https://www.elastic.co/guide/en/elasticsearch/reference/6.3/indices-open-close.html</a></p>
  
  <blockquote>
    <p>A closed index has almost no overhead on the cluster (except for maintaining its metadata), and is blocked for read/write operations.</p>
  </blockquote>
  
  <p>I am trying to optimise ES for writing a lot of data, i.e. 100K messages per second. Every hour new index is created and older indexes are not used for writing anymore. However reading from older indexes is possible.</p>
  
  <p>Should I close old indexes to optimise writing and the open them on demand if I need to perform search on them?</p>