This would probably have to be A Suitable Boy, by Vikram Seth. Or maybe The Jewel in the Crown Raj quartet by Paul Scott, a book which contained all four novels (hence, the quartet). Hmmm, both books about India or set in India. No coincidence there (see the Mahabharata). I guess I’d have to get an exact measurement to be sure.
I enjoyed both of these books. I read the Raj quartet slightly faster, but quite enjoyed taking almost 2 months to read A Suitable Boy. I like long books, as it seems that the longer time you spend with characters, the most you find you like them. India is a big country, with a lot of people, and a long history that is diverse in the way that trying to tell the history of Europe all together would be, so it makes sense for books about India and set in India to be long.