Filtering Before vs After ANN (EXPLAINED)
Hard vector DB topic: filter-aware ANN, post-filter recall collapse, and hybrid query planning for tenant isolation.
TL;DR — Quick Answer
Post-filtering runs ANN then applies metadata filters — simple but recall collapses when matches are rare in top-k. Pre-filtering restricts the search space first — better precision for selective filters but needs filter-aware indexes or brute-force fallback. Production systems use native filtered ANN (where supported) or adjust k dynamically when post-filtering.
The Interview Question
Should metadata filters apply before or after approximate nearest neighbor search? Explain pre-filtering vs post-filtering.
Deep Explanation
Post-filtering
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