title: ElasticSearch - How does sharding affect indexing performance?
body: <p>I'm doing some benchmarks on a single-node cluster of ElasticSearch.</p>
  
  <p>I faced to the situation that more shards will reduce the 
  indexing performance -at least in a single node- (both in latency and throughput)</p>
  
  <p>These are some of my numbers:</p>
  
  <ul>
  <li>Index with 1 shard it indexed +6K  documents per minute</li>
  <li>Index with 5 shards it indexed +3K documents per minute</li>
  <li>Index with 20 shards it indexed +1K documents per minute</li>
  </ul>
  
  <p>I had the same results with bulk API. So I'm wondering what's the relation and why this happens?</p>
  
  <p>Note: I don't have the resource problem! Resources are free (CPU &amp; Memory)</p>