Added some comments to snapshot implemention
Added some comments to snapshot implemention

colemancda/MRProgress,zaubara/MRProgress,zaubara/MRProgress,boherna/MRProgress,zaubara/MRProgress,yungfan/MRProgress,boherna/MRProgress,odyth/MRProgress,jackywpy/MRProgress,odyth/MRProgress,AlexanderMazaletskiy/MRProgress,jackywpy/MRProgress,mrackwitz/MRProgress,yarry/MRProgress,AddAloner/MRProgress,AlexanderMazaletskiy/MRProgress,AddAloner/MRProgress,yarry/MRProgress,yungfan/MRProgress,mrackwitz/MRProgress,colemancda/MRProgress,hanangellove/MRProgress,hanangellove/MRProgress