thundering herd problem

Scheduler thrashing. This can happen under Unix when you have a number of
processes that are waiting on a single event. When that event (a connection
to the web server, say) happens, every process which could possibly handle
the event is awakened. In the end, only one of those processes will actually
be able to do the work, but, in the meantime, all the others wake up and
contend for CPU time before being put back to sleep. Thus the system
thrashes briefly while a herd of processes thunders through. If this starts
to happen many times per second, the performance impact can be significant.

