Throttling in two browser windows at the same time causes inaccurate page load times
Reported by
t...@theo-nicolaou.co.uk,
May 31 2017
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Issue descriptionUserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:53.0) Gecko/20100101 Firefox/53.0 Steps to reproduce the problem: 1. Open a website e.g. www.mywebsite.com and in a new tab, another to compare to e.g. test.mywebsite.com 2. For both windows open Dev tools and select Good 2G throttling. 3. Refresh each window individually, note the DOMContentLoaded values for both 4. Refresh www.mywebsite.com and then test.mywebsite.com as soon as possible, so that they are loading at (roughly) the same time. 5. Note the DOMContentLoaded values for both What is the expected behavior? I would expect that the DOMContentLoaded values should be roughly the same for each website, regardless of whether they are loading at the same time or individually What went wrong? I have noticed that if the two browser windows are being throttled at the same time, the DOMContentLoaded values are significantly higher than if the windows are throttled individually. Did this work before? No Chrome version: 58.0.3029.110 (Official Build) (64-bit) Channel: n/a OS Version: 10.0 Flash Version:
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Jun 1 2017
Isn't that because they interfere? For example, they can reach the maximum number of simultaneous connections to the same host, so some requests will have to wait for others to finish. Same would happen on the real slow network - sites will share the connection.
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Jun 4 2017
Understood, but how would I go about testing my changes vs my Production environment if the throttling setting affects multiple connections - using Dev Tools is the easiest and quickest way to indicate if a performance-related change has had a positive impact, without having to set up private instances of (e.g.) WebPageTest. Just an idea but is it feasible to be able to set a flag/option where you can enable/disable the effect on simultaneous connections? Or are there any other ways around it?
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Jun 5 2017
I think the only reliable way is to not open multiple pages connecting to the same site at once. Does that work for you?
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Jun 5 2017
Unfortunately not - the issue occurs when I am connecting to a Prod URL and a sub-domain of that URL, (e.g. www.mywebsite.com and test.mywebsite.com), so I can understand why they might possibly be deemed as the same site, but the problem also happens when I am connecting to (for example) Prod and my local testing environment (e.g www.mywebsite.com and localhost). They are completely different domains so I'm not sure why there would be interference in this case?
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Jun 12 2017
It's hard to say what causes interference in case of two distinct origins without any data. Perhaps, the host network is not good enough? Did you try loading both without throttling? Does it have similar effect?
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Jun 15 2017
Without throttling enabled, the URL's load as normal even when loading simultaneously |
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Comment 1 by pfeldman@chromium.org
, Jun 1 2017Status: Assigned (was: Unconfirmed)