问题
I'm testing my pagespeed everyday several times. My page often receives a grade between 94 to 98, with the main problems being:
Eliminate render-blocking resources - Save 0.33
Defer unused CSS - Save 0.15 s
And in Lab data, all values are green.
Since yesterday, suddenly page speed has dropped, to about 80-91 range, with the problems being:
Eliminate render-blocking resources - Save ~0.33
Defer unused CSS - Save ~0.60 s
And it is also saying my First CPU idle is slow ~4,5ms
And so is time to interactive , ~4.7
And sometimes speed index is slow as well.
It also started to show Minimize main-thread work advice, which didn't show earlier.
The thing is, I did not change anything in the page. Still same HTML, CSS and JS. This also not a server issue, I don't have a CPU overuse problem.
On Gtmetrix I'm still getting the same 100% score and same 87% Yslow score, with the page being fully loaded somewhere between 1.1s to 1.7s, making 22 HTTP requests in total size of 259kb, just like before.
On Pingdom I also get the same 91 grade as before, with page load speed around 622ms to 750ms.
Therefore, I can't understand this sudden change in the way Google analyzes my page. I'm worried of course it will affect my rankings.
Any idea what is causing this?
回答1:
it seems that this is a problem of PageSpeed Insights web itself as it is reported now on some pagespeed insights discuss google groups: https://groups.google.com/forum/#!topic/pagespeed-insights-discuss/luQUtDOnoik
The point is that if you try to test your performnce direclty from another lighthouse web test, for example: https://www.webpagetest.org/lighthouse You will see your previous rates
In our case, in this site we always had 90+ on mobile but now google page rate has been reduced to 65+ https://developers.google.com/speed/pagespeed/insights/?url=https%3A%2F%2Fwww.test-english.com%2F&tab=mobile but it still remains 90+ in webpagetest.org: https://www.webpagetest.org/result/190204_2G_db325d7f8c9cddede3262d5b3624e069/
回答2:
This bug was acknowledged by Google and now has been fixed. Refer to https://groups.google.com/forum/#!topic/pagespeed-insights-discuss/by9-TbqdlBM
From Feb 1 to Feb 4 2019, PSI had a bug that led to lower performance scores. This bug is now resolved.
The headless Chrome infrastructure used by PageSpeed Insights had a bug that reported uncompressed (post-gzip) sizes as if they were the compressed transfer sizes. This led to incorrect calculations of the performance metrics and ultimately a lower score. The mailing list thread titled [BUG] [compression] Avoid enormous network payloads / Defer unused CSS doesn't consider compression covered this issue in greater detail. Thanks for Raul and David for their help.
As of Monday Feb 4, 5pm PST, the bug is completely addressed via a new production rollout.
来源：https://stackoverflow.com/questions/54504141/google-page-speed-drop-says-i-can-save-more-loading-time-even-though-nothing-c