```ruby
class ChangeHandlerToMediumTextOnDelayedJobs < ActiveRecord::Migration
  def change
    change_column :delayed_jobs, :handler, :mediumtext
  end
end
```

Use mediumtext in migration only if using mysql
user
```ruby
class ChangeHandlerToMediumTextOnDelayedJobs < ActiveRecord::Migration
  def change
    if ActiveRecord::Base.connection.adapter_name == 'MySQL'
      change_column :delayed_jobs, :handler, :mediumtext
    end
  end
end
```
assistant