Both have 123 commits, and both started in 2011. Bogdan has been active through to this year, while Alexey had a shorter period of involvement, from 2011 to 2013.
The biggest theme in Bogdan’s contributions has been the ActiveSupport callbacks, which he edited 25 times. He also did a lot of work around ActiveRecord associations. Alexey seems to have been more of an all-around Rails committer, adding bugfixes, tests, and documentation throughout the stack. The most-used word in his commit messages was “fix,” with 56 uses, where Bogdan had a tie between “association” and “callbacks” for his most-used word, with 29 uses each.
Both these guys have contributed enough work to Rails that just figuring out the key themes in that work is an interesting challenge. For that, they deserve the gratitude of every Rails developer out there, so let me say on the community’s behalf, thank you both very much!