Correction: In my eagerness to see the end of aggregators, I mistook the
intention. Both A and B leave aggregators in place until there is a
replacement. In which case, I am strongly in favor of B. As soon as we can
remove aggregators, I think we should.

On Wed, Oct 12, 2016 at 10:48 AM Kenneth Knowles <> wrote:

> Huzzah! This is IMO a really great change. I agree that we can get
> something in to allow work to continue, and improve the API as we learn.
> On Wed, Oct 12, 2016 at 10:20 AM Ben Chambers <>
> wrote:
> 3. One open question is what to do with Aggregators. In the doc I mentioned
> that long term I'd like to consider whether we can improve Aggregators to
> be a better fit for the model by supporting windowing and allowing them to
> serve as input for future steps. In the interim it's not clear what we
> should do with them. The two obvious (and extreme) options seem to be:
>   Option A: Do nothing, leave aggregators as they are until we revisit.
>   Option B: Remove aggregators from the SDK until we revisit.
> I'd like to suggest removing Aggregators once the existing runners have
> reasonable support for Metrics. Doing so reduces the surface area we need
> to maintain/support and simplifies other changes being made. It will also
> allow us to revisit them from a clean slate.
> +1 to removing aggregators, either of A or B. The new metrics design
> addresses aggregator use cases as well or better.
> So A vs B is a choice of whether we have a gap with no aggregator or
> metrics-like functionality. I think that is perhaps a bit of a bummer for
> users, and we will likely port over the runner code for it, so we wouldn't
> want to actually delete it, right? Can we do it in a week or two?
> One thing motivating me to do this quickly: Currently the new DoFn does
> not have its own implementation of aggregators, but leverages that of
> OldDoFn, so we cannot remove OldDoFn until either (1) new DoFn
> re-implements the aggregator instantiation and worker-side delegation (not
> hard, but it is throwaway code) or (2) aggregators are removed. This
> dependency also makes running the new DoFn directly (required for the state
> API) a bit more annoying.

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