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Lighthouse in Chrome limits maximum parallel HTTP2 connections
See original GitHub issueThis baffled me for quite a while and I think I was able to pin it down to lighthouse being the problem. Also, I tested this multiple times and it seems to be reproducable.
Thanks for the awesome work on lighthouse!
Steps
- Open URL which is served via HTTP2.
- Open network panel in the devtools.
- Disable cache and reload the page.
- Open the audits panel and run any audit.
- Run 1 to 3 again.
What is the current behavior?
- ad 3.) The network waterfall diagram shows quite all resources being downloaded in parallel. (HTTP2 multiplexing works)
- ad 4.) When inspecting the trace of the audit, maximum parallel connections seem limited to 6 or something. (HTTP2 multiplexing not working?)
- ad 5.) The network waterfall diagram shows parallel connections to all resources limited to 6 or something, even after the audit was finished/closed.
What is the expected behavior?
- ad 4.) I expect lighthouse to not limit parallel connections on HTTP2 for the audit.
- ad 5.) I expect Chrome to download all resources in parallel, but it seems the parallel connection restriction introduced by running a lighthouse audit is still in place.
Environment Information
Lighthouse: 4.2.0
Chrome: 74.0.3729.108 (Official Build) (64-bit)
OS: Windows 10 Pro 1809 (64-bit)
Issue Analytics
- State:
- Created 4 years ago
- Reactions:2
- Comments:5 (1 by maintainers)
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Thanks @juliquiron but this issue is not related to PSI.
I can’t reproduce a difference in download behavior after running Lighthouse.
I tried something else out… in a fresh chrome profile i used
chrome://net-export/and then loaded https://http2.akamai.com/demo (and sometimes just https://http2.akamai.com/demo/h2_demo_frame.html)I see a few things. I see 6 sockets opened to h1 and just 2 opened to h2. (I haven’t run Lighthouse at all, so this is conceivably default behavior).
I’m also assuming you weren’t using applied throttling, because it’s just too disruptive for this sort of analysis.
Given that, though… I imagine it was a weird situation of visualization.
Will close for now.
If anyone can provide a URL where I can test this, I’d happily reopen.