When mod_pagespeed launched in November 2010, one of its benefits was to help websites better exploit browser caching by signing URLs with the resource content hash. This improves the user experience coming back to the same site, and navigating within a site.
Your web page loads faster when JQuery is preloaded in users' browser
Resolving DNS entries early for critical assets saves hundreds of milliseconds
DNS resolution time varies from <1ms for locally cached results, to hundreds of milliseconds due to the cascading nature of DNS. This can contribute significantly to total page load time. Below is a WebPagetest waterfall showing how DNS lookup time can affect page load time.
Improved performance by optimizing external resources and progressive JPEG
In addition to these new capabilities, mod_pagespeed 1.2 can proxy and optimize resources from trusted domains. This feature enables you to optimize resources even from servers that don't run mod_pagespeed. Beyond compressing and cache-extending such resources, this can improve performance of sites running SPDY where the best practices for performance are to serve all resources from the same domain (see mod_spdy).
Further, convert_jpeg_to_progressive is now a ‘core’ filter. Large JPEG images are now transcoded to progressive. This both improves the browser experience and makes such files smaller.
To see more details about the release, check out the release notes and mod_pagespeed download page.
Joshua Marantz runs Google’s PageSpeed team in Cambridge, MA, which is dedicated to making the web faster for everyone. Josh has been working on making software run fast for several decades, at Google and before that on accelerated chip simulation.
Bharath Bhushan works on making website performance better. He has a Masters in CS from IIT Madras, India.
Posted by Scott Knaster, Editor