AI long term memory database

Hello. I was thinking if i am using an api like deepseek for example and i want to make a database for myself to save data that i want the AI to remember example: If i said sara is my friend and her birthday is 2002 06 21 lets say. and i want to save this data somehow the by an algorithm that builds the api request get this data when it is within the context. hopefuly this explains it. In short terms: like a long term memory custom from client side.

issuses:

what kind of data should be stored

how it will be stored

how to navigate the data if it gets too big

how to determine what data should be added to the context when doing the api call.