This Saturday, March 21st, 2015 at 12PM UTC we will be upgrading a large portion of our database infrastructure in order to further ensure a fast and reliable GitHub experience.
To minimize risk to customer data, the site will enter maintenance mode while the upgrade is performed. HTTP, API, and Git access to GitHub.com will be unavailable during this window, which we estimate will last no longer than 15 minutes. During the maintenance we will update our MySQL Server version, as well as move a large portion of our data to an isolated cluster. This will improve scalability and help sustain the growth of our data.