Jason from Elastic here. A shard can handle concurrent writes from clients, there are multiple write threads scaling to the number of logical processors expose

Jason from Elastic here. A shard can handle concurrent writes from clients, there are multiple write threads scaling to the number of logical processors exposed to Elasticsearch, and we have invested in making Lucene accommodate this concurrency[0][1][2]. [0]: http://blog.mikemccandless.com/2011/05/265-indexing-speedup-with-lucenes.html http://blog.mikemccandless.com/2011/05/265-indexing-speedup-... [1]: https://issues.apache.org/jira/browse/LUCENE-3023 https://issues.apache.org/jira/browse/LUCENE-3023 [2]: http://blog.mikemccandless.com/2017/07/lucene-gets-concurrent-deletes-and.html http://blog.mikemccandless.com/2017/07/lucene-gets-concurren... Disclaimer: I am an engineer on the Elasticsearch team; I welcome any and all feedback.