How to sort a large text file alphabetically?

Question

So I have a text file and I need to sort the lines alphabetically. Example input:

This is the first sentence
A sentence here as well
But how do I reorder them?

Output:

A sentence here as well
But how do I reorder them?
This is the first sentence

Here's the thing: This file is so large, I don't have enough RAM to actually split it into a list/array. I tried to use Python's built-in sorted() function and the process got killed.

To give you an idea:

wc -l data
21788172 data

Answer 1

It sounds like you need to do a merge-sort: divide the file into blocks, sort each block, then merge the sorted blocks back together. See Python class to merge sorted files, how can this be improved?