Google: Cache Is King

Google fetishizes speed because websites that respond rapidly promote better user satisfaction, engagement, and monetization. Other Web-oriented companies share this obsession, but Google talks about speed incessantly and works constantly on software to make the Web faster.

Last week, Google released its open-source mod_pagespeed software to improve the performance of websites served using Apache servers. On Monday, the company revisited its favorite topic at the HTML5 Developer Conference, which runs through Tuesday in San Francisco, Calif.

In his keynote presentation, Steve Souders, performance evangelist at Google, argued that website owners need to pay more attention to the way their websites cache resources.

[ Learn more about the need for speed. Read Google Officially Speeds Up Web Page Loads. ]

In the course of his talk, "Cache Is King," Souders explored how browser cache behavior influences webpage load times. While this may sound like technical esoterica, it's actually fundamental to the way that Web users experience websites.

Think of the caching behavior as a measure of distance to a retail store: A store that's located near a community is likely to see more customers from that group than a store that's many miles away. On the Web, a slow website is like a faraway store. Any serious Web business wants its website to be immediately accessible.

The browser cache stores Web resources -- graphics files, JavaScript files, CSS files, HTML files -- when a user visits a website, to make the site load more efficiently on a return visit. Having Web resources stored on a local device makes network issues matter less. Much of the appeal of native apps on mobile devices comes from the fact that application resources tend to be stored locally from the outset, which makes the app more responsive.

According to Souders, caching has more impact on page load times than disabling JavaScript or moving from a 1.5 Mbps DSL connection to a 20Mbps FIOS connection. Tests he conducted indicate that a webpage with a baseline load time of 7.65 seconds could be reduced to a load time of 3.46 seconds through optimized caching. Switching from DSL to Fios only resulted in a 4.13 second load time.

Caching also reduced the amount of data that needed to be sent over the network to load the sample page from 904 KB to 163 KB. Savings of that sort matter a lot to mobile network operators and to users dealing with mobile data caps.

With more efficient caching, a large number of websites could become significantly more responsive. Souders says that among the Alexa top 300,000 websites, 44% have no cache control header to instruct visitors' browsers how to cache files. Among the Alexa top 1000, 24% have no cache control header.

Souders advises Web developers to be explicit about how website resources should be handled. Not every file can or should be cached, but specifying which files should be cached and how long they should be cached is work that will pay off in the long run.