OK, so my throwaway comment made it to HighScalability.com's weekly links, so I feel compelled to cite my sources: https://arstechnica.com/information-technolo

OK, so my throwaway comment made it to HighScalability.com's weekly links, so I feel compelled to cite my sources: https://arstechnica.com/information-technology/2012/04/exclusive-a-behind-the-scenes-look-at-facebook-release-engineering/ https://arstechnica.com/information-technology/2012/04/exclu... Quote: Because Facebook's entire code base is compiled down to a single binary executable, the company's deployment process is quite different from what you'd normally expect in a PHP environment. Rossi told me that the binary, which represents the entire Facebook application, is approximately 1.5GB in size. When Facebook updates its code and generates a new build, the new binary has to be pushed to all of the company's servers. Moving a 1.5GB binary blob to countless servers is a non-trivial technical challenge. After exploring several solutions, Facebook came up with the idea of using BitTorrent, the popular peer-to-peer filesharing protocol. BitTorrent is very good at propagating large files over a large number of different servers. Rossi explained that Facebook created its own custom BitTorrent tracker, which is designed so that individual servers in Facebook's infrastructure will try to obtain slices from other servers that are on the same node or rack, thus reducing total latency. Rolling out a Facebook update takes an average of 30 minutes—15 minutes to generate the binary executable and another 15 minutes to push the executable to most of Facebook's servers via BitTorrent.