Due to the nature of distributed processing, order is not preserved. You can, however, inspect the PaneInfo to determine if an element was early, on-time, or late and act accordingly.
On Tue, Feb 12, 2019 at 5:15 PM Juan Carlos Garcia <[email protected]> wrote: > In my experience ordering is not guaranteed, you may need apply a > transformation that sort the elements and then dispatch them sorted out. > > Or uses the Sorter extension for this: > > https://github.com/apache/beam/tree/master/sdks/java/extensions/sorter > > Steve Niemitz <[email protected]> schrieb am Di., 12. Feb. 2019, 16:31: > >> Hi everyone, I have some questions I want to ask about how windowing, >> triggering, and panes work together, and how to ensure correctness >> throughout a pipeline. >> >> Lets assume I have a very simple streaming pipeline that looks like: >> Source -> CombineByKey (Sum) -> Sink >> >> Given fixed windows of 1 hour, early firings every minute, and >> accumulating panes, this is pretty straight forward. However, this can get >> more complicated if we add steps after the CombineByKey, for instance >> (using the same windowing strategy): >> >> Say I want to buffer the results of the CombineByKey into batches of N >> elements. I can do this with the built-in GroupIntoBatches [1] transform, >> now my pipeline looks like: >> >> Source -> CombineByKey (Sum) -> GroupIntoBatches -> Sink >> >> *This leads to my main question:* >> Is ordering preserved somehow here? ie: is it possible that the result >> from early firing F+1 now comes BEFORE the firing F (because it was >> re-ordered in the GroupIntoBatches). This would mean that the sink then >> gets F+1 before F, which means my resulting store has incorrect data >> (possibly forever if F+1 was the final firing). >> >> If ordering is not preserved, it seems as if I'd need to introduce my own >> ordering back in after GroupIntoBatches. GIB is an example here, but I >> imagine this could happen with any GBK type operation. >> >> Am I thinking about this the correct way? Thanks! >> >> [1] >> https://beam.apache.org/releases/javadoc/2.10.0/org/apache/beam/sdk/transforms/GroupIntoBatches.html >> >
