title: Unable to recreate a mongo index with the same name
body: <p>I have an index which i need to modify.</p>
  
  <pre><code>    {
      "v" : 1,
      "key" : {
          "expectedDateTime" : 1
      },
      "name" : "expectedDateTime_1",
      "ns" : "expectation.expectation_data",
      "expireAfterSeconds" : 43200
  }
  </code></pre>
  
  <p>The expireAfterSeconds is incorrect and needs to be changed to 432000.</p>
  
  <p>When I dropped the index it seemed fine</p>
  
  <pre><code>db.expectation_data.dropIndex({"expectedDateTime":1})
  { "nIndexesWas" : 4, "ok" : 1 }
  </code></pre>
  
  <p>The getIndexes() shows that the index does not exist.</p>
  
  <p>Then when i try to recreate the index i get this error</p>
  
  <pre><code>db.expectation_data.createIndex({"expectedDateTime":1}, 
  {expireAfterSeconds:432000,name:"expectedDateTime"});
  {
      "ok" : 0,
      "errmsg" : "Index with name: expectedDateTime already exists with different options",
      "code" : 85
  }
  </code></pre>
  
  <p>Now on running getIndexes(), i see that the index seems to have recreated with the old TTL. I tried repeating this process multiple times, but ran into the same issue again and again.</p>
  
  <p>I cannot find any documentation which says that i cannot recreate an index of the same name. If i use a different name it works fine</p>
  
  <pre><code>db.expectation_data.createIndex({"expectedDateTime":1}, {expireAfterSeconds:432000});
  .
  .
  &gt;db.expectation_data.getIndexes()
  .
  .
  {
      "v" : 1,
      "key" : {
          "expectedDateTime" : 1
      },
      "name" : "expectedDateTime_1",
      "ns" : "expectation.expectation_data",
      "expireAfterSeconds" : 432000
  }
  </code></pre>
  
  <p>Is there any restriction on recreating indexes with the same name ?</p>