It is any kind of invariant. Look for calls to die().
Most commonly it happens when allocating memory fails. That throws an exception, which is caught, and then a possibly guilty connection is closed, some memory deallocated and life hopefully goes on. Except that if the wrong connection is closed the memory situation may not improve... I want to close the oldest connection in addition to the current choice, but haven't written the code to do that yet.
Arnt
