Google PageSpeed Service Reviewed

With defer_javascript on, browser-reported page load times tell less of the picture. The problem is that what browsers report back to your analytics service is the amount of time that passes before the onload event while defer_javascript [1] postpones javascript execution until the onload event. This means that with defer_javascript off you were counting javascript execution time but when you turned it on you stopped counting it.<p>We're trying to optimize something like "time until the page is visually complete and usable", and there's not currently a good metric for that. Speed index [2] does visual completeness well, but I don't know of any algorithmic way to measure time-until-usable.<p>(I work on the PageSpeed team at Google, mostly on ngx_pagespeed.)<p>[1] <a href="https://developers.google.com/speed/docs/mod_pagespeed/filter-js-defer" rel="nofollow">https://developers.google.com/speed/docs/mod_pagespeed/filte...</a><p>[2] <a href="https://sites.google.com/a/webpagetest.org/docs/using-webpagetest/metrics/speed-index" rel="nofollow">https://sites.google.com/a/webpagetest.org/docs/using-webpag...</a>

&#62; Not to be confused with mod_pagespeed, which is an Apache module<p>PageSpeed Service proxies your site, but aside from that the optimizations it makes are very similar to mod_pagespeed (and ngx_pagespeed). Which makes sense: they're closely related Google projects.<p>(I work on all three, but mostly ngx_pagespeed these days.)

I'm not sure the "cloudflare has been getting worse and worse" that links to a single page written by you referencing a single twitter post. Really helps the article any.<p>However it was mostly a terrible read.

It would be interesting to know what the before/after load time histograms look like. The averages that New Relic give can hide a lot of the details of what's actually happening.<p>Rant on why averages are bad for looking at performance data: <a href="http://highscalability.com/blog/2012/5/23/averages-web-performance-data-and-how-your-analytics-product.html" rel="nofollow">http://highscalability.com/blog/2012/5/23/averages-web-perfo...</a>

Getting rid of javascript altogether and sticking with validating html5 worked for me.

It's a great article, thanks a lot for sharing this. The most amazing part of all of it is that Google offers it for free while many other companies charge a lot of money for the same (or even worse) functionality.

this was a poorly written article. random numbers all over the place, no understanding from author about how the services actually work. awful.