Using apport (id 1088183) - the highest frequency commentator.
correlated cold 7000ms hot 6300ms uncorrelated cold 8000ms hot 6500ms
Using id 165 - an id that has commented on one bug correlated cold 1100ms uncorrelated 72ms
So I'd go with the uncorrelated (the IN rather than the EXISTS) query.
Using apport (id 1088183) - the highest frequency commentator.
correlated cold 7000ms hot 6300ms
uncorrelated cold 8000ms hot 6500ms
Using id 165 - an id that has commented on one bug
correlated cold 1100ms
uncorrelated 72ms
So I'd go with the uncorrelated (the IN rather than the EXISTS) query.