I thought the matching happened with elements in the matching window, in
Event time, not in Processing time.
Granted, I'm not that familiar with this area myself, but one key part of
Beam is nearly everything is Event time by default, not Processing time.
On Tue, Apr 27, 2021, 12:43 AM Jan Lukavský <je...@seznam.cz> wrote:
> Hi,
>
> I have a question about matching side inputs to main input. First a
> recap, to make sure I understand the current state correctly:
>
> a) elements from main input are pushed back (stored in state) until a
> first side input pane arrives (that might be on time, or early)
>
> b) after that, elements from the main input are matched to the current
> side input view - the view is updated as new data arrives, but is
> matched to the main input elements in processing time
>
> If this is the current state, my question is, would it be possible to
> add a new mode of matching of side inputs? Something like
>
> ParDo.of(new MyDoFn()).withSideInput("name", myView,
> TimeDomain.EVENT_TIME)
>
> the semantics would be that the elements from the main PCollection would
> be stored into state as pairs with the value of the current main input
> watermark and on update of side-input watermark only main input elements
> with associated input watermark less than that of the side input would
> be matched with the side input and sent downstream. Although this
> approach is necessarily more expensive and introducing additional
> latency than processing time matching, there are situations when
> processing time matching is inapropriate for correctness reasons.
>
> WDYT?
>
> Jan
>
>
