Take a look at OptiKlean by DigiTalking (on Github). I’ve been using this plugin for around 3 months to take out the trash and optimize my databases. One of my setups is about 5 years old and had gotten sluggish (very) and optimizing the database regularly has brought the machine back to life. https://www.reddit.com/r/kodi/comments/1kug67h/i_have_created_an_addon_for_cleaning_and/
Link leads to a good description and comments from users.