It can work in pull mode when it is a side input, via Combine.globally().asSingletonView(). Then the default is produced when the side input is requested and there is no data found.
Kenn On Thu, Nov 21, 2019 at 10:32 AM Reuven Lax <re...@google.com> wrote: > In particular, since windows can be data based (e.g. session windows) the > set of windows is not always knowable in advance. > > On Thu, Nov 21, 2019 at 10:29 AM Robert Bradshaw <rober...@google.com> > wrote: > >> The semantics are a bit undefined--the sane extension of the model to >> support this is that the default value would show up in every window >> (otherwise which window would the default value belong to), but we >> don't have support for enumerating windows (or truncating infinite >> collections in batch mode). >> >> On Thu, Nov 21, 2019 at 4:55 AM Robin Qiu <robi...@google.com> wrote: >> > >> > Hi all, >> > >> > When I run a Combine.globally() transform with a default value set, on >> a PCollection windowed by a FixedWindow, I got this error message: >> > >> > java.lang.IllegalStateException: Default values are not supported in >> Combine.globally() if the input PCollection is not windowed by >> GlobalWindows ... >> > (from here) >> > >> > Is this unsupported because it is not implemented yet, or is this a >> design decision to not support default values with windows other than >> GlobalWIndow (e.g. because the semantics is not well defined)? Where can I >> learn more about this? >> > >> > Best, >> > Robin >> >
