The number of clients. If specified, the executor factory
function returned by local_executor_factory will be configured to have
exactly num_clients clients. If unspecified (None), then the function
returned will attempt to infer cardinalities of all placements for which
it is passed values.
The maximum fanout at any point in the aggregation hierarchy. If
num_clients > max_fanout, the constructed executor stack will consist of
multiple levels of aggregators. The height of the stack will be on the
order of log(num_clients) / log(max_fanout).
The number of distinct client executors to run
concurrently; executing more clients than this number results in multiple
clients having their work pinned on a single executor in a synchronous