Figure 1a shows how incidents happened substantially less on Saturday and Sunday even though traffic to the site remains consistent throughout the week. Figure 1b shows a six-month period during which there were only two weeks with no incidents: the week of Christmas and the week when employees are expected to write peer reviews for each other.
These two data points seem to suggest that when Facebook employees are not actively making changes to infrastructure because they are busy with other things (weekends, holidays, or even performance reviews), the site experiences higher levels of reliability.
Via Lobsters [1], “Graham King » Facebook’s code quality problem [2]”
I guess Facebook's [3] old motto of “move fast and break things [4]” was probably not the best motto [5] a company could have.
[1] https://lobste.rs/s/4gf4cr/facebook_s_code_quality_problem
[2] http://www.darkcoding.net/software/facebooks-code-quality-problem/
[5] http://mashable.com/2014/04/30/facebooks-new-mantra-move-fast-with-stability/#bzLDCWCUFsqT