What if, in the days leading up to Christmas, a crush of shoppers forced a retailer to lock its doors during peak business hours? Unimaginable--but that's exactly what happened to varying degrees at the Web stores for Wal-Mart, Macy's, and other retailers as the holiday e-commerce season got off to a blazing start. Here's what's more shocking: There's no guarantee it won't happen again during the all-important shopping days ahead, when even bigger throngs are expected at e-retail sites.

You'd think retailers would have licked the problems of site downtime and slow response times by now, even during the holiday rush. Yet while everything else associated with online shopping keeps rising--the number of visitors, sales volume, site sophistication, and consumer expectations--site performance is still a wild card. As companies load up on Ajax- and Flash-powered interactive features that can stress sites, simple uptime and performance could be the differentiators this season.

	No Ajax here Photo by Stephen Chernin

Wal-Mart's failure on Black Friday, the day after Thanksgiving, was the most stunning. Walmart.com was down for a total of about 10 hours that day, according to Internet monitoring firm Keynote Systems, forcing it to greet shoppers at times with a "come back later" notice. "I'm afraid it was too much of a good thing on Friday," a Wal-Mart spokesman says. Wal-Mart expected order activity to be double the level on last year's Black Friday, but it came in at seven times the previous year's volume. Wal-Mart set big online goals for this holiday season, having spent 13 months adding faster checkouts and an interactive toy section, the kind of features it hopes will lure about 300 million visitors this holiday season. Not if the door's closed it won't.

Macy's site performed poorly for about nine hours on Black Friday, according to Keynote, and was down for about an hour that day and then again part of the following Tuesday. Zappos' and Foot Locker's sites also had some performance problems. Keynote says most sites, including Wal-Mart's, recovered Monday and didn't have major problems that day.

Stores that kept their sites up did blockbuster business. Online buying on so-called Cyber Monday--thought of as the start of the Web shopping season, the theory being people start buying from their computers at work stuff they saw in stores over the weekend--totaled $608 million, up 26% from the same day last year. That made it the biggest single day in retail e-commerce history, says comScore Networks. On the Friday after Thanksgiving, online retail spending was up 42% over the previous year, comScore says.

WHEN THINGS GO WRONG

With the Web bringing in increasingly significant sales, why are retailers still dropping the ball on site performance? In most cases, they aren't. Many conduct load testing, forecasting, and monitoring using tools from companies such as Keynote and Gomez, and they use content distribution networks from companies such as Akamai Technologies and Netli to speed performance. They build their e-commerce infrastructures with an eye on performance, with redundancy at common failure points. But sites can still fail.

One reason is that the various teams--marketing, site designers, QA testers--too often aren't watching or sharing the same metrics, says Matthew Poepsel, VP of professional services at Gomez. If groups worry only about their metrics--marketing pushes a promotion, for instance, without being sure site design and capacity can handle it--you have "individual success but collective failure," he says. When a problem hits, Poepsel says, 80% of the recovery time is spent identifying the problem. "Once you know what the problem is, you can get it fixed pretty quickly, unless it's a sheer bandwidth issue and you need to cut a new contract," he says.

While Barnes & Noble's site has been performing fine in recent days, the problems of some other retailers don't surprise site CTO David Willen. "It just shows the incredible complexity it takes to power these Web sites," he says.