Round 1(Bar Raiser):
Complete discussion on my project.
Suppose you have a file with billion entries and you have to sort the data of a file according to a column and can put only that column in memory and after putting that your memory gets full.
e.g. your file contains

1. cut the big file to small files. the number of small files can be equal  big file divide memory size. 2. sort each small file separate.3. external sort  using min-heap.