Re: [I] [Bug]: Side Input Singleton View throw error when impulse period is short: PCollection with more than one element accessed as a singleton view [beam]

["yelianevich (via GitHub)" <gi...@apache.org>]

yelianevich commented on issue #26465:
URL: https://github.com/apache/beam/issues/26465#issuecomment-1929855207

   @ballooncross Looking at your code I can suggest an alternative approach by using a custom global combiner that will eliminate subsequent `Latest.globally()` and `View.asSingleton()` and will do everything in one step.
   
   ```
   PCollectionView<Map<String, String>> map = pipeline.apply("Impulse", 
                                                GenerateSequence.from(0).withRate(1, Duration.standardSeconds(1)))
                   .apply(Window.<Map<String, String>>into(new GlobalWindows())
                           .triggering(Repeatedly.forever(AfterProcessingTime.pastFirstElementInPane()))
                           .discardingFiredPanes())
                   .apply(Combine.globally(new MaxImpulseFn<>(functionToRead, coderOfFunctionOutput))
                        .withoutDefaults()
                        .asSingletonView());
   ```
   `MaxImpulseFn` is a custom combiner (even though quite simple) that finds the max impulse and reads the external data in `extractOutput`
   ```
   private static class MaxImpulseFn<T> extends CombineWithContext.CombineFnWithContext<Long, Long, T> {
   
          @Override
           public T extractOutput(Long accumulator, Context context) {
               return functionToRead.apply(accumulator, context.getPipelineOptions());
           }
   
           @Override
           public Coder<T> getDefaultOutputCoder(CoderRegistry registry, Coder<Long> inputCoder) {
               return coderOfFunctionOutput;
           }
   }
   ```


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