Niya,
Works well enough for every website in the world. Works well enough for banks. Works well enough for just about every accounting software on the planet. Works well enough for every computerized POS system on Earth. Works well enough for the CIA, FBI, and the NSA. Save yourself all this headache and use a DB.
File accesses are very slow, compared to an in-memory array access, limited by the spin rate of the disk, plus many other system factors. I'm trying to find a way to access a large body of data at speeds comparable to a RAM access.