Why my tmux was laggy: the status bar was forking a 1.2 GB server 24 times a second
My tmux had started to feel sluggish. Nothing was broken, it just felt heavy. It turned out the tmux server was using about a third of a CPU core all the time, and nearly all of that went on the status bar. Part of the cost came from the clock workaround in my previous post.
This post covers how I tracked it down, including two wrong guesses, and the fix, which brought the server from ~35% CPU to ~4% without restarting it.

