title: Merging different alembic revision heads fails on heroku
body: <p>I'm working to modify a <a href="https://github.com/wdm0006/cookiecutter-flask" rel="nofollow">cookiecutter</a> Flask app.</p>
  
  <p>locally I have deleted the migration folder and sqllite db a couple of times during development. I've pushed my chnages to heroku.</p>
  
  <p>When trying to migrate the heroku postgresdb :</p>
  
  <pre><code>$ heroku run python manage.py db upgrade
  .....
  alembic.util.CommandError: Multiple head revisions are present for given argument 'head'; please specify a specific target revision, '&lt;branchname&gt;@head' to narrow to a specific head, or 'heads' for all heads
  </code></pre>
  
  <p>following <a href="http://alembic.readthedocs.org/en/latest/branches.html" rel="nofollow">http://alembic.readthedocs.org/en/latest/branches.html</a> I tried:</p>
  
  <pre><code>$ heroku run python manage.py db merge heads
  Running python manage.py db merge heads on myapp... up, run.9635
    Generating /app/migrations/versions/35888775_.py ... done
  </code></pre>
  
  <p>Then I tried:</p>
  
  <pre><code>$ heroku run python manage.py db upgrade
  Running python manage.py db upgrade on myapp... up, run.7021
  INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
  INFO  [alembic.runtime.migration] Will assume transactional DDL.
      ....
      "%s@head" % branch_label if branch_label else "head")
  alembic.util.CommandError: Multiple head revisions are present for given argument 'head'; please specify a specific target revision, '&lt;branchname&gt;@head' to narrow to a specific head
  , or 'heads' for all heads
  </code></pre>
  
  <p>How can I merge the revision heads into one and make sure this is synced with my development version?</p>