Gmail could be unavailable for more than 21 hours in a day, and Google could still tell you that according to their SLA, the service has had 100% uptime.

It sounds impossible, but it’s a direct consequence of how Google has written its SLA for Google Apps (which includes Gmail, Google Docs, Google Calendar and more). We will explain this in detail further down, but let’s first look at what the SLA actually says.

What the Google Apps SLA says

Here are the key parts, quoted from the Google Apps SLA, emphasis added by us:

“Downtime Period” means, for a domain, a period of ten consecutive minutes of Downtime. Intermittent Downtime for a period of less than ten minutes will not be counted towards any Downtime Periods.

[...]

“Monthly Uptime Percentage” means total number of minutes in a calendar month minus the number of minutes of Downtime suffered from all Downtime Periods in a calendar month, divided by the total number of minutes in a calendar month.

So, “downtime periods” are what’s ultimately used for counting the uptime percentage for Google Apps, and these downtime periods ignore all downtime that lasts less than 10 minutes.

A worst-case scenario

Now back to our initial statement. How does the SLA make it possible to have more than 21 hours of downtime in a day and yet Google would call it 100% uptime?

Here is the problem: What if Google Apps was down for 9 minutes, up for 1 minute, down 9 minutes, etc. That would mean 54 minutes of downtime each hour, but Google still wouldn’t count it because none of the individual downtimes lasted 10 minutes of more.

Over a day (24 hours), that’s 21 hours and 36 minutes of downtime that Google would simply ignore when calculating the final uptime percentage.

Above: Red is downtime, green is uptime. Note that none of the downtime periods above last 10 minutes or more and thus are not counted according to the Google Apps SLA.

It’s an extreme and very unlikely worst-case scenario, but we wanted to illustrate the consequence of how Google’s SLA sums up its downtime and calculates its uptime percentage.

A more likely scenario

Now let’s take a much more likely example of intermittent problems:

3m, 8m, 12m, 5m, 9m, 14m, 4m = 57 minutes of actual downtime

But Google would only count this as 26 minutes of downtime, including only the downtime periods lasting 12 and 14 minutes.

Above: In this scenario, only the downtime periods lasting 12 and 14 minutes (marked with yellow) would be counted according to the Google Apps SLA.

Short outages are common in the real world

The problem with the Google Apps SLA is that short outages, less than 10 minutes in length, are actually very common in the real world.

As you may know, we here at Pingdom run an uptime monitoring service, and we know from our own experience (and a LOT of data from thousands of sites) that it’s much more common for sites to have multiple short intervals of downtime instead of a few long ones.

The 99.9% monthly uptime guarantee in the Google Apps SLA allows for 43 minutes of downtime in a 30-day month, but ignoring problems that last less than 10 minutes at a time will definitely make it much easier for Google to honor its SLA.

It’s a common scenario: A new website launches after having built up a lot of hype around its service or product, only to almost immediately crash due to overwhelming traffic. These launch troubles are almost always scalability-related.

We see this happening a lot. It may sound like a luxury problem (wow, too many users!), but think about it: If you’ve created something special and spent lots of effort building up expectations and buzz around your product, you don’t want anything to stand in the way of people finally trying it out, do you?

Here are some real-world launch troubles from 2008, and advice on how to avoid these kinds of problems.

Read more

Since 2002, Google has honored 25 historical people with custom-made versions of the Google logo, displayed for one day on the Google homepage.

Judging by the people Google have selected so far, don’t expect any WWF wrestling stars to show up anytime soon. It’s an elite collection of highly influential scientists, artist and architects who have made their mark on human history and culture.

Here they are, all 25 of them, in reverse chronological order.

Read more

Every year, companies find that someone has registered domain names involving their trademarks, or variations of their domain names that are confusingly similar to the original. If a solution can’t be found by talking to the registrant of the offending domain name(s), a formal dispute usually follows.

WIPO, the World Intellectual Property Organization (an agency of the UN), has an arbitration and mediation center for domain disputes, and they continually publish the results of these disputes, as well as related facts and figures.

We have summarized some of the most interesting data in this article, and we have also tried to figure out the underlying reason for the increase in domain disputes. Well, at least we have a pretty good theory involving Google AdSense…

Read more

Many of the major websites have localized versions of their pages for different countries. Most of the time it’s just a plain translation of their “regular” website (for example Apple Japan, Yahoo Japan and MSN Japan, to name just a few), but sometimes localization is taken a BIG step further.

Read more

First of all, a big thank you to all our readers. We hope we have been able to provide you with interesting, fun and thought-provoking articles over the past year, and if you have discovered this blog recently, thank you for joining our ranks!

We have published more than 200 posts in 2008. Since we won’t be updating the blog until next Monday (December 29), here is a selection of our very best and most popular posts from 2008 to keep you entertained in the meantime.

Read more