A method for semantic search includes receiving a query vector including a semantic feature value for each of a plurality of semantic feature dimensions. A cluster is selected from a plurality of different candidate clusters held in a relatively fast memory, each candidate cluster including a plurality of compressed answer vectors. A subset of the plurality of compressed answer vectors are promoted as candidate answers. For each of the candidate answers, a corresponding uncompressed answer vector is retrieved from a relatively slower memory. A selected answer is promoted from among the candidate answers.