Image scaling: measure time to first byte
We recently introduced metrics that measure duration for serving rescaled images (both logged out and exported to Prometheus.) The problem with these latencies is that they include the time it takes to write the byte stream in full to the client. This means that slow clients such as a mobile phones downloading an image over a poor data connection will create outliers or might otherwise skew these results, making these measurements imprecise when gauging raw scaler performance.
One option to address this could be to instead measure the time it took until the first byte is written, so that subsequent data transfer that is dependent on network quality is not taken into account.
Edited by Matthias Käppler