static DELAY: [Duration; 3] = [Duration::from_millis(1), Duration::from_millis(2), Duration::from_millis(5)];
let mut tries = 0;
let t = loop {
    match context.sql_pool.begin().await {
        Ok(t) => break Ok(t),
        Err(e) if tries == 3 => break Err(e),
        _ => { tokio::time::sleep(DELAY[tries]).await; }
    }
    tries += 1;
}?;