R – How would you implement a “last seen” feature for users


On Stack Overflow, the profile page lists a "last seen" property. This doesn't seem to be updated on every page view (for performance reasons, obviously). How would you implement it in a heavy-traffic web app? Would you update it only on certain pages? Or cache the last time you logged the user's last visit and wait a specific amount of time before updating the database? Or something completely different?

Best Solution

On a heavy-traffic site like Stack Overflow, I would only update the "last seen" variable when a user actually does something. Lurking around and reading questions and answers shouldn't count as a user being "seen" by the system. Asking and answering questions, or voting on them should be actions that update when a user is last seen.

I won't talk about the implementation details because that's already covered by other answers (and I would probably get it wrong).

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