Which decision should never be made from a cache alone?

Options

• ✗ Which trending topics to show
• ✓ Whether a seat is still free when a fan pays for it Correct
• ✗ Which avatar URL to show for a user
• ✗ Which product page HTML to serve

Why

A cache can be stale or lose writes, so two buyers could both see the seat as free. The final check belongs in the database, as one conditional write; the cache can still serve the seat map people browse.

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