Conversation

... there might be others I'm forgetting, but the longest-time "book I'm in the middle of", in the sense of "I started it, and I can remember the actions and characters and plotlines and stuff enough that if I picked it up I'd probably skim until I found where I was and continue, rather than start over",

is River Of Gods, by Ian McDonald.

From.. a few months shy of ten years ago, I think.