The Content Relevance: The Candidate Set Is Destiny - Part 2
How retrieval silently determines what a ranker can ever choose
Imagine hiring the world's best editor and asking her to choose the ten most important books for a reader—then giving her a cart filled only with airport thrillers.
Her ordering may be flawless. The recommendations will still be narrow.
This is the hidden reality of large-scale ranking systems. Product discussions tend to focus on the final score, but the final ranker sees only a tiny fraction of the available universe. Before it can be precise, the system must decide where to look.
That is retrieval.
From billions to hundreds.
At the scale of a social or entertainment platform, scoring every available post, video, song, creator, or show with the most sophisticated model is computationally impossible. Production systems therefore use a funnel.
A simplified version looks like this:
- Eligibilityremoves items that cannot be shown because of policy, privacy, geography, age,...
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