A feed cache stores each user's feed as a list of post ids, and the posts themselves in a separate cache. Why split them?

Options

• ✗ Ids compress better than posts
• ✓ An edited post is updated in one place, not in every feed that contains it Correct
• ✗ It lets the cache skip TTLs
• ✗ Posts cannot be stored in a list

Why

A popular post can be in millions of feeds. Copying whole posts would make every edit, like count or deletion a million-way write; with ids, the feed lists stay small and the post objects change once.

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