Suppose you are given a CSV file every hour containing Time_Stamp,Movie_Name,User_Rating, etc , of millions of movies(approx 100gb). And you have to find top 10 highest rated movies upto that hour . Write code to solve problem ??

I cleared 1 online assessment and 2 tech interview but, was rejected in the final round because i got stuck with this problem :(
For future please guide me how to prepare for such problems. I think it is too much for fresher position :|?