I have ~300 text files that contain data on trackers, torrents and peers. Each file is organised like this:
tracker.txt
time torrent
If you could use C++, you should take a look at Boost flyweight.
Using flyweight, you can write your code as if you had strings, but each instance of a string (your tracker name, etc.) uses only the size of a pointer.
Regardless of the language, you should convert the IP address to an int (take a look at this question) to save some more memory.