Hi Shen, The most obvious use case to me would be a pipeline that is generated by a program that loops out the input PCollections. Of course, it is quite easy to work around this by adding an empty PCollection to the flatten, so I don't think it is important.
Kenn On Thu, May 11, 2017 at 11:24 AM, Shen Li <[email protected]> wrote: > Hi, > > The FlattenTest enforces that Flatten transform can handle empty input. Is > there any use case for this feature? > > https://github.com/apache/beam/blob/release-2.0.0/sdks/ > java/core/src/test/java/org/apache/beam/sdk/transforms/ > FlattenTest.java#L128 > > How should a runner translate an empty Flatten? Should it be a > BoundedSource that emits a single watermark of value > BoundedWindow.TIMESTAMP_MAX_VALUE? > > Thanks, > > Shen >
