minstrel/internal/db/migrations/0061_fingerprint_settings.up.sql

-- 0061_fingerprint_settings.up.sql — fingerprinting's knobs, in admin
-- Settings: anything an admin might tune is a database row, changed without a
-- restart. Singleton in the style of reacquisition_settings (0056).
CREATE TABLE fingerprint_settings (
    id                          boolean PRIMARY KEY DEFAULT true,

    -- Fingerprinting new files, the backfill, and the duplicate sweep. Off
    -- stops the decode work entirely — the reason to turn it off is a slow NAS.
    -- On by default: without it the library cannot tell its duplicates apart.
    enabled                     boolean NOT NULL DEFAULT true,

    -- Seconds of audio fpcalc fingerprints. Chromaprints taken at different
    -- lengths cannot be compared, which is why track_fingerprints records the
    -- length each row was taken at (below): change this and every chromaprint
    -- is re-derived, and until then only rows at the new length are compared.
    chromaprint_length_sec      integer NOT NULL DEFAULT 120,

    -- The most disagreement two aligned fingerprints may show and still be
    -- proposed as one recording. Unrelated audio sits near 0.5, so the ceiling
    -- stays well clear of it.
    acoustic_max_bit_error_rate double precision NOT NULL DEFAULT 0.15,

    -- Files the backfill decodes at once. Decoding competes with playback
    -- transcoding for CPU and with streaming for the mount.
    backfill_concurrency        integer NOT NULL DEFAULT 2,

    -- The least time between duplicate sweeps. A sweep still runs only when
    -- fingerprints have changed since the last one.
    sweep_interval_hours        integer NOT NULL DEFAULT 1,

    -- When the settings were last saved. A new threshold or length can change
    -- what a sweep finds, so a save makes a sweep due.
    updated_at                  timestamptz NOT NULL DEFAULT now(),

    CONSTRAINT fingerprint_settings_singleton CHECK (id = true),
    CONSTRAINT fingerprint_settings_length_range
        CHECK (chromaprint_length_sec >= 30 AND chromaprint_length_sec <= 600),
    CONSTRAINT fingerprint_settings_threshold_range
        CHECK (acoustic_max_bit_error_rate >= 0.01 AND acoustic_max_bit_error_rate <= 0.35),
    CONSTRAINT fingerprint_settings_concurrency_range
        CHECK (backfill_concurrency >= 1 AND backfill_concurrency <= 8),
    CONSTRAINT fingerprint_settings_sweep_interval_range
        CHECK (sweep_interval_hours >= 1 AND sweep_interval_hours <= 168)
);
INSERT INTO fingerprint_settings (id) VALUES (true) ON CONFLICT (id) DO NOTHING;

-- Every row written so far was taken at fpcalc's default length.
ALTER TABLE track_fingerprints ADD COLUMN chromaprint_length_sec integer NOT NULL DEFAULT 120;