Send server-side timing info for debugging/tracing #272
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Sounds cool! Some of those timings are already logged on the server, and it should be straightforward to instrument the rest. The real feature here is getting server-side timings sent to the client and presenting them somehow. For a waterfall-style presentation we would need start/end times relative to the beginning of the request as well as durations. This is straightforward to get for all timing events that happen in a request context. Ideas for how to send the timing info? Seems like easiest would be to just send it in the primary document like late data responses and node arrival alerts. There's a little bit of a chicken/egg problem at the end of the request there, but maybe the very tail-end timings don't matter? Could alternatively open up a secondary channel, but that's more complicated. It would be extra awesome to be able to accurately merge server/client stats in the same waterfall! Would just need an offset for the server's request start time relative to the browser's navigation timing API start time... Not sure how well we can estimate that... The more I think about this the more excited I get! Good idea @aickin! |
Yeah, that's what I was thinking. If we wanted to be really fancy, we'd send the timings down as the occur throughout the page so that the waterfall could be built and updated as the page loads. But frankly, that sounds like a lot of work for not a lot of payoff. I think I'd just put all the timings below the late arrivals and have the devtools panel say "Waiting for data..." until it comes in.
Good point! I would just punt on getting the true end-of-response time.
Not worth it. If you read out the timings after late arrivals and right before </body>, you're close enough to the end of the response.
I think that's one of those "seems not that hard but is actually functionally impossible" problems in computer science.
🎉 Yeah, the more I think about it, the more I think it could be super powerful to see the server-side waterfall with a single click in DevTools. (Makes a great demo, too... ;) |
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Redfin will be looking to tackle this soon. Stay tuned! |
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The work to do this has been merged! |
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@bharath-rengarajan has an amazing chrome plugin that generates a waterfall graph from the server timing data. Gotta get that into this repo and up on the chrome store! |
I've been thinking about a new dev happiness feature for react-server that could be quite neat: server-side timing info.
The idea is to send down timing info of critical events on the server, including but not limited to:
Hopefully, these timings could be combined to create a DevTools panel that visualizes the server-side waterfall. This could answer questions like:
I think this could be quite a powerful feature for debugging SSR. What do you think?
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