title: Rails - don't rollback certain parts of a transaction
body: <p>Is it possible to not rollback some parts of a transaction?</p>
  
  <p>I'm trying to use an <code>after_validation</code> hook in a somewhat complex codebase where numerous parts are wrapped in a big transaction block. However, I want to save a log entry, regardless of whether the transaction as a whole fails and gets rollback.</p>
  
  <p>I can't use <code>after_rollback</code> either, because that never gets called in certain instances. </p>