title: Duration of PostgreSQL ALTER COLUMN TYPE int to bigint
body: <p>Let's say I have a table that has an <code>id</code> that is an <code>INTEGER GENERATED BY DEFAULT AS IDENTITY</code></p>
  
  <p>I'm looking to document how to change the type, if in the future an <code>integer</code> is too small and I need to change the id type from <code>integer</code> to <code>bigint</code>. I'm mainly worried about the time complexity of the change, since it will likely occur when there number of rows in the table would be near the maximum number an integer type can store.</p>
  
  <p>What would the time complexity for the following command be?</p>
  
  <pre><code>ALTER TABLE project ALTER COLUMN id TYPE BIGINT;
  </code></pre>