How does metadata filtering work in a vector database, and why can a selective filter destroy your recall?
Every RAG design says 'just filter by tenant_id.' Almost nobody can explain why that one line can quietly cut recall in half. The answer is in what the filter does to the ANN graph.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
Every RAG design says 'just filter by tenant_id.' Almost nobody can explain why that one line can quietly cut recall in half. The answer is in what the filter does to the ANN graph.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
