Recently, I encountered a situation where MySQL gave error messages that I had never seen before:

2018-12-12T14:36:45.571440Z 0 [ERROR] Error log throttle: 150 'Can't create thread to handle new connection' error(s) suppressed
2018-12-12T14:36:45.571456Z 0 [ERROR] Can't create thread to handle new connection(errno= 11)
2018-12-12T14:37:47.748575Z 0 [ERROR] Error log throttle: 940 'Can't create thread to handle new connection' error(s) suppressed
2018-12-12T14:37:47.748595Z 0 [ERROR] Can't create thread to handle new connection(errno= 11)

I was thinking maybe we hit some

ulimit

 limitations or similar, but all the usual suspects were set high enough, and we were not even close to them.

After googling and discussing with the customer, I found they had had similar issues in the past, and I learned something new. Actually it is relatively new, as it has been around for a few years but is not that well known. It is …