title: Concurrent db table indexing through alembic script
body: <p>Is it possible to create concurrent indexes for DB table through alembic script?</p>
  
  <p>I'm using postgres DB, and able to create concurrent table indexes through sql command on postgres prompt.(create index concurrently on  ();) </p>
  
  <p>But couldn't find way to create same through Db migration(alembic) script. If we create normal index(not concurrent) , it'll lock DB table so can't perform any query in parallel. So just want to know how to create concurrent index through alembic(DB migration) script </p>