This isn't an issue that's been affecting me since this last patch was applied, so I don't think that's the issue.
I'm generally able to play DayZ at around 30 FPS. Yesterday, I played for a good 4 hours or so, and my performance worked perfectly fine. At one point, I went into a big city and had a firefight, during which my performance was about 15 FPS, and since then, I've been dealing with massive lag spikes, lasting anywhere from a fraction of a second to 5 seconds, and now, my game won't even play, as the screen freezes a few seconds after I join.
Is there some sort of cache I can clear for the game? Could it be server-side? Whatever is the issue, it's made the game completely unplayable.