I'm not sure about the details about spanner, but one thing still remember - it was much cheaper to read stale data (<10secs ago), as it would've been available

I'm not sure about the details about spanner, but one thing still remember - it was much cheaper to read stale data (<10secs ago), as it would've been available from any server, not just the leader, and also that transactions were limited to 20mb or was it 40mb. Although that was 8 years ago, so things might be different now.