Web masters, listen up. MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) and Harvard University researchers have developed a system that decreases Web page-load times by 34%.
MIT News reports that the project dubbed “Polaris,” determines how to overlap the downloading of a page’s objects, such that the overall page requires less time to load.
According to PhD student Ravi Netravali, who is the 1st author on a paper on Polaris that he will present at this week’s USENIX Symposium on Networked Systems Design and Implementation, it can take up to 100 milliseconds each time a browser has to cross a mobile network to fetch a piece of data. “As pages increase in complexity, they often require multiple trips that create delays that really add up. Our approach minimizes the number of round trips so that we can substantially speed up a page’s load-time.”
The paper’s co-authors include graduate student Ameesh Goyal & Professor Hari Balakrishnan, as well as Harvard Professor James Mickens, who started working on the project during his stint as a visiting professor at MIT in 2014. The researchers evaluated their system across a range of network conditions on 200 of the world’s most popular websites, including ESPN.com, NYTimes.com (The New York Times), and Weather.com.
Traditionally, before you type in a URL, your browser doesn’t actually know what the page looks like. To load the page, the browser has to reach across the network to fetch “objects” such as HTML files, JavaScript source code, & images. Once an object is fetched, the browser evaluates it to add the object’s content to the page that the user sees.
The problem is that browsers can’t actually see all of these dependencies because of the way that objects are represented by HTML. As a result, browsers have to be conservative about the order in which they load objects, which tends to increase the number of cross-network trips & slow down the page load.
What Polaris does
What Polaris does is automatically track all of the interactions between objects, which can number in the 1000s for a single page. For example, it notes when one object reads the data in another object, or updates a value in another object. It then uses its detailed log of these interactions to create a “dependency graph” for the page.
Mickens offers the analogy of a travelling businessperson. When you visit one city, you sometimes discover more cities you have to visit before going home. If someone gave you the entire list of cities ahead of time, you could plan the fastest possible route. Without the list, though, you have to discover new cities as you go, which results in unnecessary zig-zagging between far-away cities.
“For a Web browser, loading all of a page’s objects is like visiting all of the cities,” Mickens says. “Polaris effectively gives you a list of all the cities before your trip actually begins. It’s what allows the browser to load a webpage more quickly.”
Polaris is particularly suited for larger, more complex sites. The system, says the team, is also valuable for mobile networks, since those tend to have larger delays than wired networks.
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