Function retrieve 

pub async fn retrieve<F, Fut>(
    cache: &Mutex<LruCache<String, Vec<u8>>>,
    sql: &str,
    command: &Command,
    persist: bool,
    f: F,
) -> Result<Vec<u8>>
where
    F: FnOnce() -> Fut,
    Fut: Future<Output = Result<Vec<u8>>>,