CREATE TABLE capacity_samples (
    entity_kind text NOT NULL CHECK (entity_kind IN ('share', 'pool', 'disk')),
    entity_id text NOT NULL CHECK (length(entity_id) BETWEEN 1 AND 128),
    entity_name text NOT NULL CHECK (length(entity_name) BETWEEN 1 AND 255),
    source_id text NOT NULL CHECK (length(source_id) BETWEEN 1 AND 128),
    sampled_at timestamptz NOT NULL,
    observed_at timestamptz NOT NULL,
    used_bytes bigint NOT NULL CHECK (used_bytes >= 0),
    capacity_bytes bigint NOT NULL CHECK (capacity_bytes >= 0),
    PRIMARY KEY (entity_kind, entity_id, source_id, sampled_at)
);

CREATE INDEX capacity_samples_history_idx
    ON capacity_samples (entity_kind, entity_id, sampled_at DESC);