title: sequence number vs version number in elasticsearch
body: <p>I am reading the concepts of elasticsearch-7.4 and I got to know about two fields. 
  <code>_seq_no</code> and <code>_version</code>. </p>
  
  <p>As per the documentation:</p>
  
  <p><strong>Version</strong></p>
  
  <pre><code>Returns a version for each search hit.
  </code></pre>
  
  <p><strong>Sequence Numbers and Primary Term</strong></p>
  
  <pre><code>Returns the sequence number and primary term of the last modification to each search hit.
  </code></pre>
  
  <p>But it is not clearing anything related to when they both will be different or same for a document. </p>
  
  <p>I created an index <code>test</code></p>
  
  <pre><code>PUT /test/_doc/_mapping
  {
    "properties": {
      "total_price" : {
        "type": "integer"
      },
      "final_price": {
        "type": "integer"
      },
      "base_price": {
        "enabled": false
      }
    }
  }
  </code></pre>
  
  <p>I am updating the full document using <code>PUT API</code>.</p>
  
  <pre><code>PUT /test/_doc/2
  {
    "total_price": 10,
    "final_price": 10,
    "base_price": 10
  }
  </code></pre>
  
  <p>Both <strong><em>_seq_no and _version are increasing</em></strong> in this case. </p>
  
  <p>On doing partial updates using <code>UPDATE API</code>,</p>
  
  <pre><code>POST /test/_doc/2/_update
  {
      "doc" : {
          "base_price" : 10000
      }
  }
  </code></pre>
  
  <p><strong><em>Both _seq_no and _version are increasing</em></strong> in this case too. </p>
  
  <p>So, I am unable to find the case when only one field is changing but the other is not. <br> 
  When will both the fields be different?</p>