Add 'updated_at' index to sequences and activities to speed up index.
user
```ruby
class AddIndexesToLightweightActivitiesAndSequences < ActiveRecord::Migration
  def change
    add_index "lightweight_activities", ["updated_at"], :name => "lightweight_activities_updated_at_idx"
    add_index "sequences", ["updated_at"], :name => "sequences_updated_at_idx"
  end
end
```
assistant