So when you’re debugging a problem and using tail -f my.log the last thing you expect to find is the debugging you’re looking for simply isn’t there.
Well that’s what I had today and it turned out that tail -f
After much digging I found that kqueue write events would never fire for files > 2GB due to use of int for file offset comparison in event checking code.
This was introduced by introduction EVFILT_VNODE for all filesystems over 10 years ago by r147198
I fixed it with r287886 but it was definitely one of those WTF moments when I first discovered tail -f was the cause of my debugging info not being displayed.