sparse vectors

A deceptively short interview question that's really a trap: embeddings cannot do exact match, and the interviewer knows it. What to actually turn on (payload full-text indexes, sparse vectors, metadata filters) in the vector DBs you already run.

The whole question is the representation: store only the nonzeros as index→value, then either two-pointer over sorted indices or hash-join. The follow-up that decides the design is what happens when one vector is dense.