seems only takes 3 rounds for bfs, for

list ::

on source, there are enough parallelism by the time

::

is turned into subject of

ST

processing todo 52457 items
total 52457 outputs, took Duration { secs: 142, nanos: 1994000 } seconds
processing todo 376415 items
total 88444 outputs, took Duration { secs: 152, nanos: 38940000 } seconds
processing todo 124905 items
total 88444 outputs, took Duration { secs: 32, nanos: 490969000 } seconds