Pagination mobile system design interview

Feeds almost always come up in mobile system design, and pagination is where the subtle correctness questions live.

Cursor vs offset and why it matters

Prefer cursor-based pagination over offset for feeds: a cursor points at a stable position, so inserts and deletes do not cause skipped or duplicated items the way offset paging does when the underlying list shifts. Explain requesting the next page as the user approaches the end, and prefetching a page ahead for smooth scrolling.

Consistency and UX

Discuss de-duplicating items by id when pages overlap, handling pull-to-refresh by resetting to the first page, and reconciling new data at the top without losing scroll position. Cover empty, loading, and error states per page, and stale data when the feed changed server-side. These correctness and UX details are what distinguish a senior answer.

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Frequently asked

Why is cursor pagination better than offset for feeds?

A cursor tracks a stable position, so items inserted or removed do not cause the skips and duplicates that offset paging produces when the list shifts.

How do you prevent duplicate items across pages?

De-duplicate by a stable id when merging pages, since overlapping or shifting data can return the same item in more than one page.