How many notifications should be saved?

Question

In the design for an app with a basic user/post/subscribe system how many notifications should be kept before deleting old ones? Or should they all be kept?

(Note I'm referring to an in-app notification tray, not push notifications)

The back-end as a service I'm using charges for the total data stored, so I would be worried about users going inactive and accumulating tons of unread notifications which in turn could cost me, especially if they followed a lot of active users.

If you were a user that checked an app like once or twice a year, would you be put off if you only saw the last 9 notifications or some amount?

I guess another option would be to stop pushing notifications to people who hadn't logged in for like, a week or two? Not sure if this would be an effective alternate. Probably wouldn't be great for user retention, but I don't know enough about that to say.

Answer 1

There is no universal notification amount to store, the exact value should be determined for your application exclusively.

Keeping latest notifications for a short, though reasonable for your service, period of time should serve the purpose good enough.

Otherwise it won't function as a notification, but as some kind of log where different recommendations may apply depending on whether the data stays relevant when time passes.

Answer 2

Imagine there is no cost for storing the notifications. Is the experience for a user that comes back after being inactive a good one if they get every single notification? What is the job they are solving by looking at this list?

You mention user retention, so a good start would be to understand notifications on the extremes. Is a user with a number of notifications above average more engaged? Are there users with similar engagement but no notifications at all? Could you instead have the user select which events they'd rather get notifications about? Once you know this, the cost can be used to prioritize possible solutions.