title: postgreSQL concurrently change column type from int to bigint
body: <p>I have a pretty big table (around 1 billion rows), and I need to update the id type from <code>SERIAL</code> to <code>BIGSERIAL</code>; guess why?:). </p>
  
  <p>Basically this could be done with this command:</p>
  
  <pre><code>execute "ALTER TABLE my_table ALTER COLUMN id SET DATA TYPE bigint"
  </code></pre>
  
  <p>Nevertheless that would lock my table forever and put my web service down.</p>
  
  <p>Is there a quite simple way of doing this operation concurrently (whatever the time it will take)?</p>