I have 3 database tables:

* users (stores info about users e.g. email, name)
* metadata (stores data)
* activity (stores changes made to users/metadata tables)

I want to achieve the following:

* to store any change into the activity table (e.g. new user is created, a user updates the metadata table)
* to send notifications to users whenever a change into the users/metadata tables happens.

What are the libraries/method that I could use in order to achieve the desired functionalities? Thank you!