At UMD, Chris Torek hacked ^T support to the 4.2 BSD tty driver, inspired by TOPS-10/TWENEX's interrupt character that displayed the system load, current running job, etc.
But the first version didn't have any de-bouncing, and would process each and every ^T it got immediately (each of which had a lot of overhead), so on a hardwired terminal you could hold the keys down and it would autorepeat really fast, bringing the entire system to its knees, while you could even watch the load go up and up and up!
And of course whenever the system got slow, everybody would naturally start typing ^T at once to see what was going on, making it even worse.
That was a Heisenbug, where the act of measuring affects what's being measured, with an exacerbating positive feedback loop. He fixed the problem by rate-limiting it to once a second.
But the first version didn't have any de-bouncing, and would process each and every ^T it got immediately (each of which had a lot of overhead), so on a hardwired terminal you could hold the keys down and it would autorepeat really fast, bringing the entire system to its knees, while you could even watch the load go up and up and up!
And of course whenever the system got slow, everybody would naturally start typing ^T at once to see what was going on, making it even worse.
That was a Heisenbug, where the act of measuring affects what's being measured, with an exacerbating positive feedback loop. He fixed the problem by rate-limiting it to once a second.
https://en.wikipedia.org/wiki/Heisenbug
https://en.wikipedia.org/wiki/Positive_feedback