Transakcje Atomic MySQL w Anorm

Użyj withTransaction zamiast withConnection tak:

private def incrementHitCounter(urlName:String) {
  DB.withTransaction { implicit connection =>
    SQL("select @hits:=hits from content_url_name where url_name={urlName};").on("urlName" -> urlName).apply()
    SQL("update content_url_name set hits = @hits + 1 where url_name={urlName};").on("urlName" -> urlName).executeUpdate()
  }
}

A dlaczego miałbyś w ogóle skorzystać z transakcji tutaj? To również powinno działać:

private def incrementHitCounter(urlName:String) {
  DB.withConnection { implicit connection =>
    SQL("update content_url_name set hits = (select hits from content_url_name where url_name={urlName}) + 1 where url_name={urlName};").on("urlName" -> urlName).executeUpdate()
  }
}