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How to Survive Being Slashdotted

Tips on how to survive a sudden increase in Web traffic

For several hours each day, Rob Malda has the power to send tens of thousands of Web surfers hurtling toward sometimes unprepared Web sites. No, he's not some shady Eastern European extortionist; he's one of the founders and current editors of Slashdot, the blog of choice for the geek community. Working under the nickname of CmdrTaco (a reference to a Dave Barry column), Malda has been publicizing the interesting and weird of the Web since 1997.

The way Slashdot works is simple. Each day, some 500 entries are submitted through the site, usually references to interesting or quirky Web sites someone has encountered. One of the five Slashdot editors, who work in shifts, reads the submission and decides if it passes muster, and will be one of the dozen or so stories that show up on the site's front page every day.

For an unprepared site, what happens next can be a sysadmin's worst nightmare. A site that might be designed to handle a few hundred hits per day can suddenly find itself handling that many a second. In a few hours, as many as a quarter-million visitors may be trying to access the site. In short, you've been Slashdotted.

Sometimes the traffic may exhaust a month's worth of bandwidth allocation from its ISP in a few days. Sometimes the requests can plug up a limited connection. But, according to Malda, most often it's poor planning and site architecture that do people in. "The problem is, if you have any sort of complicated code on your page, that's what kills people. I generally think that sites are not dying because they fill their pipe, but because they have poorly written code," says Malda.

For a variety of reasons, the Slashdot staff doesn't give advanced warning to Slashdottees. For one thing, it can be nearly impossible to find out who runs a Web site, and with the workload of processing hundreds of submissions each day, there just isn't time to research it. In addition, Malda says that in many cases, sites would change their content if they knew they were going to be featured.

CmdrTaco can't estimate how many sites succumb to the onslaught of traffic that Slashdotting can bring. For one thing, he normally sees the sites before they've had the spotlight turned upon them. "They're always up for me," he comments wryly.

There doesn't seem to be any kind of hard and fast rule for what sites go down. "It never ceases to amaze me when we see a big site buckle. As a general rule, anybody who has a pretty good understanding of Web design, they've done a good job of learning what information to cache. What information needs to be pregenerated. So when you're actually loading a page, even if it's a complicated page that looks very dynamic and custom, on the back end of that, what they're really doing is putting together a bunch of puzzle pieces that have been pregenerated, and making the simplest, quickest decisions they possibly can."

He points out that many sites dynamically generate what could be statically cached, causing them to fork many processes to handle a single request. While this may hold up under light load, when Slashdot points its finger in their direction, the processor can quickly run out of memory trying to simultaneously handle all the requests.

Slashdot takes great pains to precache the most commonly requested content. Malda points out that the majority of the traffic is directed at the home page, and a few common customizations of the home page for registered users. By generating this content once and serving it statically, Slashdot dramatically reduces the demands placed on their processors.

Known for their in-depth coverage of open source topics, Slashdot also "eats their own dog food." The site hosts on a collection of database servers running MySQL and Web servers, all running on top of Linux. Since Slashdot is owned by ODSN, which is in turn a part of VA Software, this is not too surprising. A team of four programmers maintains the software, written in Perl.

Malda started Slashdot in his college days. Like Google and Yahoo, what started off as a diversion has now evolved into a serious business venture. When asked why Slashdot has succeeded where so many other blogs flounder, he credits the fact that they were first to market and built a good brand name before the market was flooded.

Slashdot itself is not immune to unusual traffic patterns. "Slashdot has very predictable traffic patterns," says Malda. "Until such time that something happens that's extremely unusual for us. For example, in times of great war or terrorist attack. A typical Slashdot discussion might be somewhere in the 300 to 700 comment range. During those times, perhaps we suddenly see a discussion with 4,000 comments. And our code is not necessarily optimized to handle the unusual circumstances that we don't deal with very often."

Malda says that what occasionally knocks over Slashdot is the same thing that takes down other sites. "It's not usually the raw traffic that does it, it's the traffic doing something it doesn't usually do." He goes on to say that another big problem sites create for themselves is when the graphics and HTML for a page are being served for the same machine. Because a single page may request a dozen or more graphics, and Web servers can be tuned to deliver graphics very efficiently, Web admins can avoid clogging their servers with graphics requests that could be more quickly delivered from a second machine.

Getting a story posted on Slashdot can be a real status symbol, but with 50 or 60 submissions for every posted story, it can also be a challenge. Unfortunately, according to Malda, there's no magic formula for getting a story accepted. "If I could give you a bulleted list, I could automate this and I could retire. But honestly it's not really that easy. There are a dozen different things that we look at. Is it relevant to our audience? Are we interested in it? Is it important? Is it funny? We take all of these different things and we kind of mix them together and then we basically make an arbitrary decision."

He does have one inside hint for the desperate. "You have the different human factor. I'm more interested to pick some subject matter, perhaps, than Timothy. So if you know when I'm posting stories, and you know what stories I like, you might be more likely to get a story accepted if you submit it during my shift than during Timothy's. I'm the one who's probably going to be posting a story about an interesting case mod or a handheld. I'm the gadget junkie and I'm a case mod junkie. And our shifts are pretty obvious, you just look on the site and you see who's posted four or five stories in a row."

More Stories By James Turner

James Turner is president of Black Bear Software. James was formerly senior editor of Linux.SYS-CON.com and has also written for Wired, Christian Science Monitor, and other publications. He is currently working on his third book on open source development.

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