title: Rails 4 concurrent database indexes
body: <p>I am just wondering what is the correct behaviour when creating concurrent indexes in Rails.</p>
  
  <p>I am using this in my migration file:</p>
  
  <pre><code>disable_ddl_transaction!
  
  def change
      add_index :table_name, :field_name, algorithm: :concurrently
  end
  </code></pre>
  
  <p>This should create a postgres concurrent index. </p>
  
  <p>My question is: When running <code>rake db:migrate</code> Is the correct behaviour to wait for the creation of the index? I mean, the migration will wait until the index is created? Or it should end and delegate postgres that responsibility?</p>
  
  <p>P.S. It is a really big index.</p>