Facebook is down for few moments today and all the like boxes fan pages everything went down. 500 million users have lost access to their favorite social networking site and 350,000 sites using Facebook apps to are having a bad time. People too might had a doubt that recently their was a rumor saying Facebook would be closed after march 15th. But nothing of that sort happened its all back to normal again.

Similar situation was faced during Sep 2010 and According to Facebook's software engineers Johnson's post the reasons for downtime during that time was as follows.

According to Johnson’s post, the problem stemmed from an automated system Facebook had built to check for invalid configuration values in its cache. Unfortunately, that automated check backfired — to the point that Facebook had to turn off the site entirely to recover. Here’s a portion of the explanation: Today we made a change to the persistent copy of a configuration value that was interpreted as invalid. This meant that every single client saw the invalid value and attempted to fix it. Because the fix involves making a query to a cluster of databases, that cluster was quickly overwhelmed by hundreds of thousands of queries a second. To make matters worse, every time a client got an error attempting to query one of the databases it interpreted it as an invalid value, and deleted the corresponding cache key. This meant that even after the original problem had been fixed, the stream of queries continued. As long as the databases failed to service some of the requests, they were causing even more requests to themselves. We had entered a feedback loop that didn’t allow the databases to recover. The way to stop the feedback cycle was quite painful – we had to stop all traffic to this database cluster, which meant turning off the site. Once the databases had recovered and the root cause had been fixed, we slowly allowed more people back onto the site.

I think all those Facebook addicts too had a bad time but it happens some times so be patient till the site gets completely up. Facebook is not gone anywhere it is back again.

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