What made the GMAIL go DOWN, this time - September 1, 2009?

In the recent times, GMail service going down (Temporary Error 502) seems to be happening at least once in every two months. GMail being one of the most widely used mail service in the world today, such Service Down problems aren't simply minor ones for those who rely upon GMail for their work.

Here is a summary of the incidents, from GMail's Blog, that had affected the GMail service, recently.

• GMail team made a small fraction of GMail servers down, as a part of routine maintenance.
• However the team underestimated the load that would be placed to the Router Servers (that redirect requests to appropriate GMail servers) because of this maintenance activity.
• During the maintenance work, few of the Router Servers were overloaded, which were later transferred onto other remaining Router Servers and thus the entire system was locked in few minutes.
• Only the Web access to GMail was affected. IMAP/POP access to GMail  were not affected as they don't use these router servers.
• Gmail Team have solved this problem and have taken actions to avoid similar problems in future.