When to update the data in the database?

Question

PostgreSQL

Good afternoon!
I have written an application in which data is saved in the sqlite database, there is also a functionality that synchronizes sqlite with postgres only new records. and I would also like to synchronize record updates - that is, if a record in sqlite was changed, then these changes were sent to postgres as well.
but the problem is that if I deleted the application and the local database was deleted, how then to determine which data in postgres is old and which is new? randomize a unique code every time ? that is, if the database is created on a new one and pass this code every time you update it in postgres. what mechanisms are implemented

Answer 1

1. Immediately after installing the application, do a reverse synchronization (download) from postgres to sqlite of the necessary new (see timestamp) data for the application.
2. After downloading - be sure to verify the full synchronization of data.