Monday, August 6, 2012

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Turbocharging web sites with new PageSpeed Service optimizations


By Rahul Bansal and Kishore Simbili, PageSpeed Team

We spend a lot of time working to make the web faster. Last year, we introduced PageSpeed Service, an online service that automatically speeds up loading of web pages.

We are constantly working on new optimizations (rewriters) that can make pages load even faster. Along these lines, we are introducing a new rewriter called "Cache and Prioritize Visible Content". This rewriter enables users to start interacting with the web page and consuming the content much sooner. It accomplishes this by optimizing the page as a whole using the following web page-aware techniques and with minimal configuration needed:

  • Make HTML cacheable. Typically, most web pages are not cached because they contain small amounts of personalized information or other non-cacheable data. This rewriter separates the non-cacheable portions from the HTML and enables caching for the rest of the content on PageSpeed servers. When the page is loaded, PageSpeed servers send the cacheable parts immediately while non-cacheable parts are fetched from the origin server & patched into the browser later.

  • Prioritize visible content rendering. Rendering of a modern web page requires several network resources, but not all of them are needed right away. This rewriter automatically determines and prioritizes the content that is above the fold of the browser, so that it doesn’t have to compete with the rest of the page.

  • Defer Javascript. JavaScript execution is deferred until page load so that it doesn’t block rendering of visible content.

  • Early deployment of these techniques has shown significant improvements in user-perceived page load times. Below is a filmstrip view that compares the loading of pages on Power Line, a US-based political commentary website.

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