'Cascading bug' crashes Twitter

Posted by Emma Woollacott

Twitter's apologised for the fact that its site was unavailable yesterday, blaming a 'cascading bug'.

From around 9.00am PDT, web users were unable to access the site, and mobile clients stopped showing new tweets. Recovery efforts brought the site back on line about two hours later.

Vice president of engineering Mazen Rawashdeh says the problem was caused by a cascading bug in one of the infrastructure components.

"This wasn’t due to a hack or our new office or Euro 2012 or GIF avatars, as some have speculated today. A 'cascading bug' is a bug with an effect that isn’t confined to a particular software element, but rather its effect 'cascades' into other elements as well," he says on the company blog.

"One of the characteristics of such a bug is that it can have a significant impact on all users, worldwide, which was the case today. As soon as we discovered it, we took corrective actions, which included rolling back to a previous stable version of Twitter."

In its early days, Twitter had a reputation for unreliability, with the 'Fail Whale' a regular sight for users. Now, though, claims Rawashdeh, the site's 99.96 percent reliable.

"In simpler terms, this means that in an average 24-hour period, twitter.com has been stable and available to everyone for roughly 23 hours, 59 minutes and 40-ish seconds," he says.

Despite intense withdrawal symptoms, no users died.