Local DNA fingerprint matcher — and how to rebuild the n-gram index

Every track you import gets a Chromaprint DNA fingerprint stored in the tracks table, then broken into n-gram hashes and indexed in dna_ngram_index. When the scanner captures audio off radio, it checks this index FIRST — only falling through to AudD when nothing matches. To rebuild the index from scratch (e.g. after a fresh restore or schema migration), run the one-shot rebuilder against your tracks table — it walks every row, regenerates hashes, and bulk-inserts into dna_ngram_index. The math: ~140 tracks → ~165k hashes → sub-10ms lookups via the (hash, source_type, source_id) index.