Online sales during this holiday season (November 21st, 2013 – January 6th, 2014) weren’t as miraculously high as retailers were hoping for but still December sales gave a lift to the US economy.

Thanksgivinig weekend was marked by a 4% decline in online sales, which is the first sales decline since 2009. On top, the 2013 holiday season between Thanksgiving and Christmas was six shopping days shorter than usual. Almost unexpectedly, however, December sales went up by 0.2%, according to the Census Bureau.

What happened in December?

"If you look at what lifted spending -- food, gasoline, clothing, online shopping -- are all things you can expect to increase when the weather is bad," said Joseph LaVorgna, chief U.S. economist at Deutsche Bank for money.cnn.com.

As weather went bad in December and people rushed on the Internet to stock themselves up with holiday gifts, clothing and food, online retailers – while happy with sales going upwards – faced another issue. They had to watch out for heavy online traffic on their websites as that could cause the websites to slow down or even bear outages. If website visitors are in a process of purchasing an item when the website slows down or interrupts, they may not be able to finish the transaction or may simply get annoyed and quickly switch to a competitor website.

We monitored 10 of the most popular online retailers during the whole holiday season to see whether they were really prepared for swift traffic shifts. And here’s what we saw:

Availability

Toysrus.com had 14 hours of downtime during the whole 47-day holiday season. In other words, some of the visitors on that website who were trying to buy gifts for their friends and family, most likely could not finish up with the purchase, and could have gone to another website.

During the same period, another online store – overstock.com – did not register any downtime at all. That website was available the whole time so anyone who tried to purchase items from it, did it successfully.

The rest of the monitored websites varied between 3 minutes and 12 hours of downtime. See their classification by downtime in the infographic below.

Performance

As for the websites’ performance, which is measured by the time it takes to load a page (i.e. response time), overstock.com demonstrated an enviable response time of 2.55 seconds. Amazon.com, on the other hand, had the highest response time of 6.8 seconds. Needless to say, the higher the response time, the more visitors are likely to lose patience and quit trying to load the page and/or purchase items.

The rest of the monitored websites varied between 2.55 and 6.55 seconds of response time.

In short, overstock.com was best prepared for traffic shifts during Holiday season 2013, bestbuy.com was second, and amazon.com was third.