[Data] Empty stats on StreamSplitDataIterators resulting from streaming_split()

[scottjlee]

What happened + What you expected to happen

The stats are missing (empty string) from DatasetIterators resulting from streaming_split(), after execution. See below for reproducible example.

Versions / Dependencies

Ray master, Python 3.9

Reproduction script

def pause(x):
    time.sleep(.0001)
    return x

ds = ray.data.range(10000)
ds = ds.map(lambda x: x)
ds = ds.map(pause)

@ray.remote
def consume(p):
    for x in p.iter_batches():
        pass

    print("Finish consume")
    stats = p.stats()
    print(f"Emit DatasetStats: {stats}")
    print(type(stats))

a, b = ds.streaming_split(2)
ray.get([consume.remote(a), consume.remote(b)])

Issue Severity

None

[ericl]

Will take a look.

[scottjlee]

Oh yeah sorry for the notification, I accidentally moved this around in the sprint planning GH project and it reassigned the issue. Thanks

[ericl]

Per user report, this doesn't include iterator stats.