Upcoming NostrNet will come with weekly auto-update notification. 

Upon clicking the notification, it will initiate the process of fetching all your data from the relays, saving a copy of it, and update your data across all relays. 

In-App database to store that data. This all happens locally, without even a external notification server
https://i.imgur.com/fiEoJjh.jpg 

 Most data isn't worth to be saved 

 Future historians will disagree